SUITABILITY ASSESSMENT OF SOILS AND CLIMATE FOR AGRICULTURE DEVELOPMENT AT MWAVI FARM, BAGAMOYO DISTRICT, COAST REGION

Transcription

1 SUITABILITY ASSESSMENT OF SOILS AND CLIMATE FOR AGRICULTURE DEVELOPMENT AT MWAVI FARM, BAGAMOYO DISTRICT, COAST REGION Joseph D.J. Mbogoni Sibaway B. Mwango MLINGANO AGRICULTURAL RESEARCH INSTITUTE P.O. BOX 5088 TANGA, TANZANIA JANUARY 2011

2 Contents EXECUTIVE SUMMARY... 3 HOW TO USE THIS REPORT Introduction Purpose Implementation Geology and physiography of the area Present land use Methodology Preparation of base maps Field studies Assessment of soil fertility status Climatic analysis Land suitability classification Map production Climate of Mwavi farm Rainfall trend Wind speed, insolation and relative air humidity Temperature Growing periods at Mwavi farm Soils of Mwavi farm General soil conditions Soils of the topographic summits and upper slopes Soils of the middle slopes Soils of the lower slopes Description of the soil mapping units Ridge summits and upper slopes Land suitability assessment Popcorn Sunflower Pigeon pea Citrus Pineapple Yellow passion fruit Malformation of fruits Summary of land suitability assessment Bibliography Munsell Color, Munsell Soil Colour Charts, Baltmore Organic matter and total nitrogen Soil reaction Cation exchange capacity (CEC) Exchangeable magnesium Exchangeable K Exchangeable sodium Soil sodicity Basic infiltration rate (IR) Available water capacity (AWC) Aluminium saturation

3 EXECUTIVE SUMMARY Soil and climatic analysis were carried out for Mwavi farm that is located in Kiwangwa ward, Msata division, Bagamoyo district, Coast region. The major objective was to establish the suitability of soils and climate for agriculture for an area covering 400ha. The main conclusions of this study and recommendations are presented. Three major topographic settings were identified on the basis of topography, drainage and soil morphology. Ridges higher on the landscape have gentle slopes (1-3% slope) and are situated at an average altitude range of m. Dominant soils of the broad ridge crests are generally moderately deep to very deep and well drained. Surface soils are 10-30cm thick sands and loamy sands. The subsoils are sandy loams, sandy clay loams and sandy clays. Soils of ridges on lower position in the landscape vary greatly over short distances in texture, depth and gravel content, forming complex soil patterns. Dominant soils are generally shallow to moderately deep and moderately well drained. Occasionally, the surface consists of fine quartz and ferruginous gravel (murram) that extend to great depth. In other areas gravel and murram occur at an average depth of 50cm from the surface. Surface soils are loamy sands and sandy loams. Subsoils are sandy loams, sandy clay loams and sandy clays that are very firm, sticky and plastic, with distinct mottling. In some places the subsoils contain CaCO 3 alongside quartz gravel. The gravel and murram layer is rather water and root restricting. Topographic middle slopes occur at an average altitude range of m. Dominant soils are generally shallow to moderately deep and moderately well drained. In some areas gravel and murram occur at an average shallow depth of 25-50cm from the surface. Surface soils are loamy sands, sands and to a lesser extent sandy loams while subsoils are sandy loams, sandy clay loams and sandy clays. In some places the subsoils contain CaCO 3 alongside quartz gravel. The gravel and murram layer is water and root restricting. Most subsoils are usually poorly aerated due to wetness during the rainy season. Lower slopes occur at an average altitude range of m. Dominant soils are very deep, moderately well drained sands, loamy sands, sandy loams and sandy clay loams. In some areas the subsoils are contain fine CaCO 3 as nodules or as coatings on quartz gravel. These soils are young and have poor structure and profile development. High ground water levels are common during the rainy season. The climate at Mwavi farm is characterized by an average yearly rainfall of about 950mm, with contrasting wet and dry seasons. During the main long rain season (masika) in March- May the amount of rain (470mm) is sufficient only for the cultivation of early maturing crops. The short rainy season (November-December) does not bring enough rain for a second crop in most years. During the dry season of 5 months (June-October) the amount of rain is generally less than 70mm per month. A second dry season occurs from January to March. The short rain season with low and unreliable rainfall is the main constraint for the cultivation of many crops. This constraint is propounded by the sandy, drought soils with 3

4 limited moisture storage capacity. Their very low organic matter status and poor fertility are additional limitations for sustained crop production with acceptable yield levels. During years with sufficient rainfall soils of the ridges (mapping units A and B) can support early maturing maize (e.g. popcorn), sunflower and pigeon pea, but the unreliable onset date of rainfall and the high risk of dry spells during critical stages of crop growth lead to crop failure can not be avoided even when other factors such as management, crop husbandry and fertilizer application are optimal. Mapcode Current suitability Constraints Potential suitability A Moderate Very low fertility Suitable B C D Moderate Marginal Marginal Very low fertility, shallow in places Very low fertility, shallow in places, high gravel content Very low fertility, shallow in places, high ground water Suitable Marginal Marginal E Unsuitable Poor aeration Unsuitable Technologies Conservation tillage, build up of organic matter, fertilizer NPK, Minjingu Mazao Conservation tillage, build up of organic matter, fertilizer NPK, Minjingu Mazao Conservation tillage, build up of organic matter, fertilizer NPK, Minjingu Mazao Conservation tillage, crop selection Conservation tillage, crop selection Test crops Popcorn, sunflower, pigeon pea, citrus, passion fruit Popcorn, sunflower, pigeon pea, citrus, passion fruit Popcorn, sunflower, pigeon pea, citrus, passion fruit Area (ha) Proportion % Pastures Pastures The main management recommendation is to increase present levels of organic matter. This can be achieved by adding good quality farm yard manure to the topsoils, green manuring, mulching and ploughing under of crop residues. Crop rotations involving legumes and cereals are advocated. Besides these practices the application of mineral fertilisers and Minjingu Mazao will be needed in order to obtain reasonable yields. On the ridge lower slopes and valleys (mapping units D and E) growing periods are somewhat longer due to the overall higher moisture storage capacity of the soils and additions of moisture by seepage from the adjacent ridges. The main constraints are surface ponding and excess soil water at shallow depth during crop growth. These lands can be profitably used for growing pastures to serve as livestock feed. The by-products such as farm yard manure will be spread to upland soils of mapping units A, B and C. Field studies are necessary to study the performance of the crops and to refine the land husbandry practices, crop selection and fertilizer recommendations. As long as the N, P, and K status of soils is not optimum, it is unlikely that substantial crop yields will be realized. 4

5 HOW TO USE THIS REPORT This volume is a technical report on Suitability Assessment of Soils and Climate for Agriculture Development of Mwavi farm. It describes in detail criteria and procedures used for collecting, storing, analysing and presentation of the environmental information and eventually land suitability assessment of the farm in a GIS environment. Whereas this report is meant to be self-supporting, it can be used alongside the soil and land suitability map. Most of the relevant information for the farm is presented in summary form in this report to ease linking of the report with the map. The conclusions and recommendations given in this report are those considered appropriate at the time of its preparation. They may be modified and/or adjusted in the light of further knowledge gained through additional research. 5

6 1. Introduction 1.1 Purpose This report presents results of a study on the soil and climatic conditions at Mwavi Farm that is located some 15km west of Bagamoyo town in Kiwangwa ward, Msata division. The farm covers about 400ha between approximately o and o Longitude East as well as 6.41 o and 6.43 o Latitude South. Objectives of the study were three-fold: Soil characterisation and mapping. Analysis of climatic conditions. Assessment of potential for agricultural development. 1.2 Implementation The study presented in this report is a semi-detailed assessment of soil and climatic characteristics of Mwavi farm and is by no means exhaustive. Field work in the area was conducted in June 2010 by Scientists from A.R.I. Mlingano namely Joseph D.J. Mbogoni (Team leader), G.J. urassa, S. J. Hiza, S.B. Mwango, C.A. Komba, E. Losujaki and S.V. Assenga. Soil samples taken during field work were analysed in the Central Soil Laboratory at Mlingano. The technical report and accompanying map were prepared by J.D.J. Mbogoni and S.B. Mwango. 1.3 Geology and physiography of the area Figure 1 presents the topography of Mwavi farm. Mwavi farm is located in a Coastal hinterland plain (CH1) that is characterised by gently undulating plains at an average altitude range of m and average relief intensity of 40m. Ridge crests are broad and nearly flat to gently undulating (0 to 3% slope). Ridge side slopes are about m long with an average slope gradient of 2-3%. Most valleys are U-shaped with narrow incisions forming seasonal water passage ways. Soils of the farm developed in Neogene sandy clays, sandstones and other terrestrial sediments. 1.4 Present land use Figure 2 present remnants of the original tropical semi-humid vegetation. The present vegetation in the farm is a secondary and tertiary bushland of miombo and bush thicket. Most of the original vegetation was cleared for charcoal making, firewood and building poles. The area is presently used for extensive grazing. A small part of the farm is cultivated with maize, pineapples and banana as presented in Figure 3. 6

7 Figure 1. Topography of Mwavi farm.

8 Figure 2. Ebony trees (Diospyros spp. Or Mpingo), Acacia spp., and grass as remnants of the original tropical semi-humid vegetation at Mwavi farm.

9 Figure 3. Maize and cassava field at Mwavi farm. 2. Methodology 2.1 Preparation of base maps The landform at Mwavi is a dissected coastal plain of almost flat (valleys and ridge summits) to undulating (ridge side slopes) topography. Accurate delineation of the various soillandscape formations was done utilising a topographic map sheet 168/3 at a scale of 1:50,000 (Government of Tanganyika, 1963). Description of the geology for the area was obtained from Quarter Degree Sheet 168 (GSD, 1963). Main landscape features elaborated on for the area were contours, ridges, valleys, streams and road network. Farm boundaries were developed by recording geographical coordinates of all know boundary points such as trees, pegs, streams. The border points were identified with assistance of Mwavi farm management and the coordinates were recorded using a GPS set. 2.2 Field studies Soils of the farm were studied by a free traverse procedure. Topographic features valleys and ridges were used as reference for locating soil observation sites using an auger. Auger observations were made to record soil morphological characteristics to a depth of 100cm. 9

10 Soil characteristics investigated were depth, drainage, colour, texture, structure, consistence, porosity and root distribution. Morphological features likely to influence drainage and rooting conditions of soils such as compaction, cementation and gravely layers were described and recorded. These observations facilitated identification of major soil types in the farm that were used to compile a soil map of the farm. Soils were described according to guidelines for soil description (FAO, 1990). From auger observations bulk soil samples were collected from soil depth sections of 0-25cm, 25-50cm, 50-75cm and cm. Based on the auger observations 7 representative sites were selected where soils were studied in detailed in deep pits. Bulk soil samples for analysis were collected from natural horizons identified in these pits. In addition to the pit samples, 11 composite topsoil (0-25cm-soil depth) samples were collected from representative areas for investigation of the soil fertility status. The sampling technique involved collection of at least five sub-samples, mixing to produce a homogenous soil material and re-sampling of the final composite sample. The soil samples were analysed at the Central Soils Laboratory in A.R.I. Mlingano following standard procedures (NSS, 1990) presented in Annex 1. A GPS set was used to record the geographical location (coordinates) of all observation and sampling sites. 2.3 Assessment of soil fertility status Analytical data for bulk samples and composite topsoil samples were used to assess the fertility status of soils. The soil fertility status (based on nutrient levels) of the soil mapping units are described in relative terms (low, medium and high) according to classification of nutrient levels for general soil fertility evaluation presented in Annex Climatic analysis Climatic data rainfall, temperature, relative air humidity, wind speed and insolation (sunshine hours) were compiled and analysed in CropWat environment utilising the Penman formula (Doorenbos and Pruitt, 1984). The major outputs of the analysis were effective rainfall, evapotranspiration, length of growing periods and dry seasons. 2.5 Land suitability classification Land suitability is the capacity of land to provide, under given levels of management, the highest returns per unit area, while conserving the natural resources for future use. Therefore land suitability classification is the appraisal and grouping of land in terms of suitability for specific uses on the basis of intermediate interpretation stage by means of the land quality concept. The best suitable lands are therefore those lands which produce the highest yields at the lowest costs. Based on this economic principle the best approach would be to determine the productive potential of each soil type. However, this approach could not be carried out as the farm does not have production data. The land suitability evaluation followed in this study has an ecological approach. Land qualities considered relevant for this study are: 10

11 Water availability in the root zone. Rooting conditions. Soil fertility. Terrain conditions. Since land qualities could not be measured, they were evaluated on the basis of land characteristics. The land suitability classes were established by matching crop and land management requirements with the land characteristics. Suitable land (S1) Land having no significant limitations to sustained application of the considered use, or only minor limitations that will not significantly reduce productivity or benefits and will not raise inputs above an acceptable level. suitable land (S2) Land having limitations that in aggregate are moderately severe for sustained application of the considered use. The limitations will reduce productivity or benefits and increase required inputs to the extent that the overall advantage to be gained from the use, although still attractive, will be appreciated inferior to that in class S1 land. Marginally suitable land (S3) Land having limitations which in aggregate are severe for sustained application of the considered use and will reduce productivity or benefits or increase required inputs, that this expenditure will be only marginally justified. suitable land (N1) Land having limitations which appear so severe as to preclude any possibilities of successful sustained use of the land in the given manner; or the limitations may be surmountable in time but cannot be corrected with existing knowledge at currently acceptable cost. 2.6 Map production All data generated during fieldwork and laboratory analysis were interpreted and compiled to thematic maps. 11

12 3. Climate of Mwavi farm Climatic data relevant for the Mwavi area was obtained from Kibaha Meteorological Station, which is the nearest weather station. 3.1 Rainfall trend Climatic data representative for the area is presented in Table 1 and the historical trend of rainfall is presented in Figure 4. During the period mean annual rainfall was mm. Since then there has been a slight decrease in rainfall with time. For example rainfall records for the period indicate a decrease of mean annual rainfall by 5.5% (mean annual rainfall mm) as compared to the last years. The data indicate also that out of 10 years only 4 years receive rainfall above 1000mm. Similar climatic trends were reported by Kips et al. (1988a, 1988b) and NSS (1987). Long rains are received during the period of March-May (57% of the annual rainfall). Peak precipitation occurs in April (238mm). Short rains are received during the period October- December (25% of annual rainfall). The short rains are generally unreliable and poorly distributed. The period June-September is the main dry season and coolest for the area. The second dry season and warmest for the area occurs during the period January-February. 3.2 Wind speed, insolation and relative air humidity Wind speed is generally uniform during the year. Higher wind speeds are experienced during the months of September, October, December and January, with October recording the highest. Lowest sunshine hours are recorded during the month of April that coincides with peak precipitation period (period of maximum cloud cover). The relative air humidity being higher than 50% during the year, is suitable for a wide range of tropical crops. 3.3 Temperature Temperatures are favourable at all times of the year. Mean minimum temperatures of o C and mean maximum temperatures of o C are favourable for a wide range of tropical annual and perennial crops. 12

13 RAINFALL (mm) Table 1. Climatic data of Mwavi farm Characteristic J F M A M J J A S O N D Wind speed km/day Mean maximum C T Mean minimum C T Sunshine Hours per day Mean RH % ETo Mm per month Effective rainfall Mm per month Mean rainfall Mm per month Source: Kibaha Meteorological Station Rainfall65-70 Rainfall J F M A M J J A S O N D MONTH Figure 4. Rainfall trend at Kibaha over the last 40 years 3.4 Growing periods at Mwavi farm Figure 5 presents growing periods at Mwavi farm. The growing period (the period during the year when rainfall exceeds 0.5ETo) in the area prevail during the period late February-early 13

14 June. This is the main growing period for the Mwavi area. During the period March - May, when rainfall exceeds ETo, a humid period prevail. The rest of the year June, July, August, September, October, November, December and January is the dry period. The months of June, July, August, September, October and November are the driest months in agrohydrological terms. Figure 4. Growing periods at Mwavi farm, Soils of Mwavi farm 4.1 General soil conditions Three major topographic settings were identified on the basis of topography, drainage and soil morphology. The major topographic units are oriented in a south-east and north-west direction parallel to drainage lines in the farm. The ridges occur in the central part with highest altitude in the north-west and lowest in the south-east part of the farm. The valleys are situated on the northern and southern parts of the farm. The valleys have narrow incisions which serve as seasonal streams. Soils of the farm developed in Neogene sandy clays, sandstones and other terrestrial sediments Soils of the topographic summits and upper slopes Most of the ridge summits have gentle slopes (1-3% slope) and are situated at an average altitude range of m. Ridges on highest position in the landscape are located on the north-western part of the farm. Dominant soils of the broad ridge crests are generally moderately deep to very deep and well drained. Surface soils are 10-30cm thick, (very) dark greyish brown sands and loamy sands with massive (breaking to single grains) to weak subangular blocky structures. The 14

15 subsoils are dark greyish brown, dark brown to reddish brown sandy loams, sandy clay loams and sandy clays. They have moderate blocky structures and support root proliferation to great depth. Ridges on lower position in the landscape are located on the middle and south-western parts of the farm. Soil properties vary greatly over short distances in texture, depth and gravel content, forming complex soil patterns. Dominant soils are generally shallow to moderately deep and moderately well drained. Occasionally, the surface consists of fine quartz and ferruginous gravel (murram) that extend to great depth. In other areas gravel and murram occur at an average depth of 50cm from the surface. Surface soils are loamy sands and sandy loams. Subsoils are sandy loams, sandy clay loams and sandy clays. Soil structure in the subsoils is generally columnar and angular blocky. The consistence is very firm, sticky and plastic, with distinct mottling. In some places the subsoils contain CaCO 3 alongside quartz gravel. The gravel and murram layer is rather water and root restricting Soils of the middle slopes Topographic middle slopes occur at an average altitude range of m. They are located on the southern and northern parts of the farm. Surface soils are generally sandy but subsoils are more clayey. Soil properties vary greatly over short distances in texture, depth and gravel content, forming complex soil patterns. Dominant soils are generally shallow to moderately deep and moderately well drained. Occasionally, the surface consists of fine quartz and murram. In some areas gravel and murram occur at an average shallow depth of 25-50cm from the surface. The texture of surface soils are loamy sands, sands and to a lesser extent sandy loams. They have massive structures that break to single grain and weak subangular blocky. Subsoils are sandy loams, sandy clay loams and sandy clays. Soil structure in the subsoils is generally columnar and angular blocky. The consistence is very firm, sticky and plastic, with distinct mottling. In some places the subsoils contain CaCO 3 alongside quartz gravel. The gravel and murram layer is water and root restricting. Most subsoils are usually poorly aerated due to wetness during the rainy season Soils of the lower slopes This is an association of soils occurring at an average altitude range of m. Dominant soils in the association are very deep, moderately well drained very dark grey to brown sands, loamy sands, sandy loams and sandy clay loams. Surface soils are over 15cm thick sands and loamy sands with massive and single grain structures. The subsoils are brown gravely sands, sandy loams and sand clay loams with weak blocky structures. Gravel consists of fine murram and quartz. In some areas the subsoils are contain fine CaCO 3 as nodules or as coatings on quartz gravel. These soils are young and have poor structure and profile development. High ground water levels are common during the rainy season. Plant roots proliferate in the upper 50cm soil depth. The second soil type in the association represent moderately deep, imperfectly and poorly drained sandy clay loams to sand clays and clays with gravely layers occurring at about 50cm soil depth. The topsoils are very dark grey loamy sands with massive structures. The subsoils 15

16 are massive, mottled, calcareous and gravely sandy clay loams and sand clays. Often these soils have groundwater at about 20-30cm soil depth during the rainy season. Plant roots proliferate in the upper 50cm soil depth. 4.2 Description of the soil mapping units Table 2 presents topographic information of the soil mapping units. Each mapping unit is described in a defined order. The first paragraph outlines the physiographic setting and gives the extent of the unit. The second paragraph describes the morphological characteristics of the soil such as colour, texture, structure, consistence and thickness of the layers. The third paragraph outlines the chemical characteristics of the topsoil and subsoil. The fourth paragraph describes the agricultural potential of the mapping unit. Table 3 presents analytical data for topsoils of the soil mapping units. Nutrient levels for the soil map are described in relative terms (low, medium and high) according to classification of nutrient levels for general soil fertility evaluation presented in Annex Ridge summits and upper slopes Mapping unit A (22.8ha or 15.2%) A complex of very deep, well drained dark greyish brown loamy sands and sandy loams over strong brown and yellowish red sandy clay loams and moderately deep to deep, moderately well drained dark greyish brown loamy sands and sandy loams over yellowish brown and grey mottled gravely sandy loams and sandy clay loams. The soil is located on a broad gently undulating ridge summit with average slope range of 1-3% and average altitude of m. The ridge summits have rather straight to convex slopes. Representative soil profiles are KWP4, KWP5, KWP15, KWP16, KWP18, KWP19, KWP20 and KWP23. Morphological and physical characteristics The average thickness of all surface horizons in the soil complex is 8-25cm, being homogenously dark greyish brown and greyish brown loamy sands to sandy loams with friable to very friable, non sticky and non plastic consistence. Structure is moderately developed to fine granular and medium subangular blocky. Subsoils of the well drained soils are strong brown and yellowish red sandy loams to sandy clay loams, with moderate medium and coarse subangular blocky structure. They are friable, slightly sticky and slightly plastic, with few fine clay coatings and many fine and medium pores. Many plant roots occur up to a depth of 50cm then decrease gradually with increasing soil depth. Subsoils of the moderately well drained soils are dark grey, yellowish brown and grey sandy loams and sandy clay loams with moderate medium to very coarse angular blocky structure. They are very firm, sticky and plastic, with many fine, medium and coarse quartz gravel in 16

17 some places. The gravely layers also have many fine and medium red and light olive brown mottles. Table 2. Topographic information of the soil mapping units in Mwavi farm Mapcode Position Altitude Slope Depth Drainage Texture Structure Area Proportion m % class class class type ha % Moderate Loamy sand to A Middle - upper slope Very deep to well sandy loam gr,sbk Moderate Loamy sand to B Middle slope - summit Deep - very deep to well sandy loam gr,sbk Moderate Sandy loam to C Upper - summit deep to well sandy clay loam gr,sbk Loamy sand to D Lower - middle slope deep Moderate sandy loam massive Moderate E Lower slope - valleys deep to poor Sandy loam to clay massive Chemical characteristics Surface soils The soils have a strongly to slightly acid reaction (ph range ). The content of basic cations calcium, magnesium and potassium is low to medium. The content of organic carbon, total nitrogen and available phosphorus is very low. The organic matter in the soil is of good quality (C/N ratio of 12 15). Subsoils Soil reaction is medium acid (ph ). Organic carbon levels (<0.60%) and total nitrogen levels (<0.1%) are very low. Available phosphorus levels (<7mg/kg) are very low. Levels of exchangeable calcium ( cmol/kg) and those of magnesium (1-2.3cmol/kg) are low to medium. Exchangeable potassium is present in very low levels (0.12cmol/kg). The organic matter is of good quality. Agricultural potential Surface soils of the mapping unit have favourable rooting conditions for a wide range of crops. The morphological properties are also favourable for both manual and mechanised land preparation. However, the sandy topsoils have naturally low available water holding capacity which is unfavourable during dry spells. Subsoils of the well drained soils have favourable morphological properties for rooting while those of the moderately well drained soils have poor rooting conditions due to inadequate aeration due to compactness and high gravel content. The overall fertility status of the mapping unit is low to very low. Sustainable cropping can be achieved with introduction of technologies suitable for rejuvenating soil fertility such as manuring, introduction of leguminous cover crops in the farming system and use of fertilisers. 17

18 Table 3. Analytical data for topsoils of Mwavi farm Mapcode ph(h2o) Org. C Total N Avail. P Ca Mg K Area Proportion 1:2.5 % % mg/kg cmol/kg cmol/kg cmol/kg ha % A <0.6 <0.1 < < B <0.6 <0.1 < < C <0.6 <0.1 < < D <0.6 <0.1 < < E <0.1 <7 > Mapping unit B (17.9ha or 11.%) A complex of moderately deep to deep, moderately well drained very dark greyish brown loamy sands over dark grey and greyish brown mottled sandy clay loams on murram and moderately deep to deep, well drained dark greyish brown loamy sands over strong brown and yellowish red slightly gravely sandy clay loams. The soil complex is situated at an average altitude of m. The unit is very gently to gently sloping (1-3% slope) and is located in the western part of the farm. The soil complex is transitional between the higher ridges of mapping unit A with lower ridges of mapping unit C. Representative soil profiles are KWP22, KWP25 and KWP28. Morphological and physical characteristics The thickness of surface soils range from 15-25cm. The surface soils of the moderately well drained soils are (very) dark greyish brown loamy sands and sandy loams with weak granular and subangular blocky structure. The soils are very friable to friable, very slightly sticky and non plastic, with common fine quartz gravel and many fine roots. Surface soils of the well drained soils are dark brown, reddish brown and dark reddish brown loamy sands and sandy loams. They have weak structure development and friable, slightly sticky and very slightly plastic consistence. Subsoils of the moderately well drained soils are dark grey, greyish brown and grey sandy clay loams with moderate, medium, coarse and very coarse angular blocky structure. The consistence is firm, sticky and plastic. They are also characterised by presence of many fine and medium yellowish red and dark red mottles that increase with depth to the murram layer. Plant roots proliferate in the upper subsoils but decrease to very few in the mottled zone. Subsoils of the well drained soils are yellowish red, brown to strong brown sandy loams and sandy clay loams with moderate medium and coarse subangular blocky structure. They are friable, slightly sticky and slightly plastic. The deeper subsoil contains many fine quartz gravel and common fine Fe/Mn concretions. The deeper subsoils are rather root restricting due to presence of significant amounts of gravel and nodules. 18

19 Chemical characteristics Topsoils The topsoils have a medium acid reaction as ph falls within the range The content of basic cations calcium, magnesium and potassium is low to medium. The content of organic carbon, total nitrogen and available phosphorus is very low. The organic matter in the soil is of good quality (C/N ratio of 12 15). Subsoils Soil reaction is strongly acid to medium acid (ph ). Organic carbon levels (<0.60%) and total nitrogen levels (<0.1%) are generally very low. The subsoils have very low levels of available P (<7mg/kg). Levels of exchangeable calcium and magnesium are low to medium. Exchangeable potassium is present in low to medium levels. Agricultural potential Rooting conditions in the upper 50cm soil depth are suitable for a wide range of annual and perennial crops. The morphological properties are also favourable for both manual and mechanised land preparation. The available water holding capacity is better than mapping unit A. Most parts of the mapping unit have low to very low fertility status. A soil fertility programme is necessary for enhancing soil productivity. Mapping unit C (44.5ha or 29.7%) A complex of moderately deep to deep, moderately well drained very dark greyish brown loamy sands over dark grey and greyish brown calcareous mottled sandy clay loams on murram and moderately deep to deep, well drained dark brown and reddish brown sandy loams over yellowish red and strong brown gravely sandy clay loams. The mapping unit is situated at an average altitude of m with a slope gradient range of 1-3%. The landscape in mapping unit has multiple slope types. These variations in slope form have hard significant influences on characteristics and distribution of soils. Representative soil profiles are KWP8, KWP9, KWP10, KWP11, KWP14, KWP29 and KWP32. Morphological and physical characteristics The thickness of surface soils range from 15-25cm. Surface soils of the moderately well drained soils are (very) dark greyish brown loamy sands and sands with granular and single grain structure. The soils are very friable to friable, non sticky and non plastic, with common fine quartz gravel and many fine roots. Surface soils of the well drained soils are dark brown, reddish brown and dark reddish brown loamy sands and sandy loams. They have moderate fine structure development and friable, slightly sticky and slightly plastic consistence. Subsoils of the moderately well drained soils are dark grey, greyish brown and grey sandy clay loams with moderate, medium, coarse and very coarse angular blocky structure. The consistence is firm, sticky and plastic. They are also characterised by presence of many fine and medium yellowish red and dark red mottles that increase with depth to the murram 19

20 layer. In some places there are common fine quartz gravel coated with CaCO 3. Plant roots proliferate in the upper subsoils but decrease to very few in the mottled zone. Subsoils of the well drained soils are yellowish red, strong brown and dark reddish brown sandy loams, sandy clay loams and sandy clays. They have moderate fine and medium structure development. The consistence is friable, sticky and slightly plastic. In some places the deeper subsoils contain fine ferruginous concretions. Chemical characteristics Topsoils The soil reaction is medium acid (ph ). The content of basic cations calcium and magnesium is medium to high while potassium is present in very low levels. The content of organic carbon, total nitrogen and available phosphorus is very low. The quality of organic matter vary greatly over short distance. Subsoils The soil reaction is medium acid to neutral (ph ). The content of basic cations is low to very high for calcium, high for magnesium while potassium is present in very low levels. The content of organic carbon, total nitrogen and available phosphorus is very low. The quality of organic matter is moderate to good. Agricultural potential The available water holding capacity is low to medium due to shallow rootable depth particularly in the moderately well drained soils due to gravel content and root restricting deeper subsoils layers. Land preparation operations are constrained by high gravel content. Most parts of the mapping unit have low fertility status. This is clearly indicated by deficiency in most of the nutrients. Soil management measures effective in restoration of soil fertility status have to be practised to improve soil productivity. Soils of the lower and middle slopes Mapping unit D (60.4ha or 40.3%) A complex of moderately deep to deep, moderately well drained dark greyish brown gravely loamy sands over greyish brown and grey mottled very gravely calcareous sandy clay loams on murram and deep to very deep, well drained very dark greyish brown loamy sands over very dark grey and grey gravely massive sandy clay loams and sandy clays. The mapping unit is situated at an average altitude of m with a slope gradient range of 1-3%. The landscape of the soil complex has multiple slope types, ranging from straight to concave and convex. Representative soil profiles are KWP1, KWP2, KWP3, KWP7, KWP12, KWP13, KWP17, KWP21, KWP24 KWP26, KWP27, KWP30 and KWP31. 20

21 Morphological and physical characteristics Figure 4 is a typical soil for the mapping unit. The thickness of surface soils range from 15-25cm. Surface soils of the moderately well drained soils are (very) dark greyish brown loamy sands and sandy loams with weak subangular blocky structure. The soils are very friable to friable, very slightly sticky and non plastic, with common fine quartz gravel and many fine roots. Surface soils of the well drained soils are dark brown, reddish brown and dark reddish brown loamy sands and sandy loams. They have moderate fine structure development and friable, slightly sticky and slightly plastic consistence. Subsoils of the moderately well drained soils are dark grey, greyish brown and grey sandy clay loams with moderate, medium, coarse and very coarse angular blocky structure. The consistence is firm, sticky and plastic. They are also characterised by presence of many fine and medium yellowish red and dark red mottles that increase with depth to the murram layer. CaCO 3 concretions are also present in some areas. Plant roots proliferate in the upper subsoils but decrease to very few in the mottled zone. Subsoils of the well drained soils are yellowish red, strong brown and dark reddish brown sandy loams, sandy clay loams and sandy clays. They have moderate fine and medium structure development. The consistence is friable, sticky and slightly plastic. In some places the deeper subsoils contain fine ferruginous concretions. Chemical characteristics Topsoils The soil reaction is medium acid (ph ). The content of basic cations calcium and magnesium is medium to high while potassium is present in very low levels. The content of organic carbon, total nitrogen and available phosphorus is very low. Subsoils The soil reaction is medium acid to neutral (ph ). The content of basic cations is low to very high for calcium, high for magnesium while potassium is present in very low levels. The content of organic carbon, total nitrogen and available phosphorus is very low. Agricultural potential The available water holding capacity is low to medium due to shallow rootable depth particularly in the moderately well drained soils due to gravel content and root restricting deeper subsoils layers. Land preparation operations are constrained by high gravel content. Most parts of the mapping unit have low fertility status as is revealed by the very low to low nutrient levels. The fertility status of soils need to be improved for sustainable productivity. 21

22 Figure 4. Soil profile KWP1 with ground water at 60cm depth. Mapping unit E (4.1ha or 2.7%) Association of moderately deep to deep, moderately well drained dark greyish brown sandy loams over black, dark grey and grey gravely sandy clay loams and moderately deep poorly drained black clays over dark grey and grey massive gravely mottled sandy clays. The mapping unit is situated at an average altitude of m, with slope gradients of 0 3%. The unit is U-shaped with narrow incisions that serve as drainage lines during the rainy season. The mapping unit occur in the north-east part of the farm. Representative soil profiles are KWP6, KWP6b, PB1 and PB2. Morphological and physical characteristics well drained soils have 20-30cm thick topsoils that are (very) sandy loams and loamy sands Soil structure is weak granular, with very friable non sticky and non plastic consistence. The surface soil is underlain by a bleached layer of brown sand. There are many pores and plant roots in this surface soil. Subsoils are black, dark grey and grey mottled sandy loams and sandy clays with massive structure, having very firm sticky and plastic consistence. The subsoils have common fine quartz gravel and murram. The soil below 50cm depth is characterised by prolonged wetness due to high ground water levels. The soil has few fine roots. The poorly drained soils have black massive clay topsoils that are firm, sticky and plastic. 22

23 Chemical characteristics Topsoils The topsoil reaction is slightly acid (ph ). The content of basic cations is high for calcium and magnesium while potassium is present in low to medium levels. The content of organic carbon is low to medium, while the levels of total nitrogen and available phosphorus are very low. Subsoils The subsoil reaction is slightly acid. The content of basic cations is medium to very high for calcium and high for magnesium. Levels of exchangeable potassium, organic carbon, total nitrogen and available phosphorus are very low. 5. Land suitability assessment The management of Mwavi farm intends to develop the land into profitable agricultural and related enterprises with reasonable investment and management costs. In order to achieve this, informed decisions on most suitable alternative agricultural land utilization types need to be made. Naturally the Management will prefer to produce high yields with relatively low inputs. Therefore the main objective for assessing agricultural suitability of Mwavi farm is to help the Management to make rational choices between land use alternatives. To satisfy this need, land suitability is assessed not only for the nature and degree of constraints but also for the feasibility of improvement measures required to mitigate the constraints. The most useful information considered in this study include water availability in the root zone, rooting conditions, soil fertility and terrain conditions. On the basis of the overriding constraint of low soil fertility, two groups of rainfed crops were selected for this study: Perennial crops - yellow passion fruits, citrus and pineapple. Annual crops Popcorn, sunflower and pigeon pea. 5.1 Popcorn Maize has a rather wide range of climatic tolerance. Early maturing varieties are able to develop with as little as 400mm of rainfall in the growing period, as against 750mm or more for late maturing varieties. The length of the growing period determines the type of maize to be grown. The maturity period of the crop should not exceed the growing period otherwise the crop may not mature due to shortage of moisture. That being the case, popcorn was selected from among the several varieties of maize. 23

24 Popcorn moves through commercial channels in three kernel types: white, small yellow and large yellow. Maximum popping potential of popcorn can be achieved only if it reaches full maturity. Any factor that prematurely terminates plant development (e.g., drought stress, disease, etc.) will reduce popping potential, and may result in a crop not marketable as popping corn. Some popcorn hybrids are dent-sterile and cannot be pollinated by ordinary types of dent or sweet corns. In popcorn seed fields where the harvested crop is to be used as seed for the following year's crop, dent sterility is important because it prevents outcrosses to dent corn. However, in popcorn production fields where the harvested crop is to be used for popping, isolation from other types of corn is unnecessary, even if the popcorn is not dent-sterile. Pollen from other corn does not have any effect on the popping ability of popcorn hybrids. Although there is little experimental data regarding effects of soil type on popcorn production, experience shows that any soil type suitable for dent corn should produce a good popcorn crop. However, experience also indicates that popcorn is likely to perform better on medium- to coarse-textured soils (coupled with adequate rainfall) than on finetextured (clays), poorly drained soils for at least two reasons: Popcorn seed germinates more slowly than dent corn, and the seedlings grow more slowly; thus, medium- to coarse-textured soils, which warm slightly faster than finetextured soils, should improve germination, emergence and seedling establishment. The popcorn root system is less extensive than that of dent corn; thus, high-claycontent and/or poorly drained soils foster weak, shallow rooting that reduces yields and increases lodging. 24

25 Table 4. Optimal environmental requirements for popcorn in coastal Tanzania compared with the actual conditions at Mwavi farm Characteristic Condition Level/range Map unit A Rainfall in Optimal 400mm in the growing 3 months period Actual 470mm in 3 months Rainfall Optimal 75mm during flowering Actual 130mm Groundwater Optimal >90cm level Physical soil conditions Soil ph (0-25cm) Natural fertility soil Map unit B Map unit C Map unit D Map unit E Actual >90cm >90cm >90cm Severely Optimal Deep well drained Actual Deep well Deep well Moderate Shallow, Deep, poor drained drained moderate Optimal Slightly Severely Actual Optimal High N and P levels Actual Very low Very low Very low Very low Low Slightly Research information on the response of popcorn hybrids to soil fertility levels is also limited. Many experienced popcorn growers apply somewhat less fertilizer than recommended for dent corn, reasoning that, since yields are lower, less fertilizer is needed. This is probably a safe practice at comparable plant densities, but it may not apply if popcorn is grown at significantly higher plant densities. Any dent corn fertilizer program being adapted to popcorn production should take into consideration popcorn's relatively poor standing ability. Very high rates of N can compound lodging problems, especially if less-thanrecommended rates of potash are used. Also, because popcorn seedlings grow more slowly than dent corn, the application of starter fertilizer is probably of greater importance. 25

26 Table 4 compares the environmental requirements for maize in coastal Tanzania with the actual conditions at Mwavi. The table shows clearly that the early maturing maize varieties stand a better chance of yielding satisfactorily than late maturing varieties. In most years the rainfall during the flowering month is too low for late maturing varieties. Dry spells of more than one week will do much damage to the crop because of the fairly low water holding capacities of the soils. Soils of Mwavi farm have very low fertility levels. Nitrogen, phosphorus and potassium (NPK) levels are very. The use of farm yard manure and crop rotations with leguminous crops providing additional nitrogen are necessary for acceptable yields. Incorporating crop residues in the soil will further add to increase levels of organic matter which at present are very low. Use of chemical fertilizers and Minjingu Mazao is necessary for optimum production of popcorn at Mwavi farm. 5.2 Sunflower Botany Sunflower (Helianthus annuus L.) is an annual, erect, broadleaf plant with a strong taproot and prolific lateral spread of surface roots. Stems are usually round early in the season, angular and woody later in the season, and normally unbranched. Sunflower leaves are phototropic and will follow the sun's rays with a lag of 120 behind the sun's azimuth (heliotropism). At sunrise, the faces of most sunflowers are turned towards the east. Over the course of the day, they move to track the sun from east to west, while at night they return to an eastward orientation. This motion is performed by motor cells in the pulvinus, a flexible segment of the stem just below the bud. As the bud stage ends, the stem stiffens and the blooming stage is reached. This property has been shown to increase light interception and possibly photosynthesis. The sunflower head is not a single flower (as the name implies) but is made up of 1,000 to 2,000 individual flowers joined at a common receptacle. The flowers around the circumference are ligulate ray flowers without stamens or pistils. The remaining flowers are perfect flowers (with stamens and pistils). Anthesis (pollen shedding) begins at the periphery and proceeds to the centre of the head. Since many sunflower varieties have a degree of self-incompatibility, pollen movement between plants by insects is important, and bee colonies have generally increased yields. Climate requirements Sunflower is grown in many semi-arid regions of the world. The average growing period is 90 to 130 days. It is tolerant of both low and high temperatures but more tolerant to low temperatures. Optimum temperatures for growth are C, but a wider range of temperatures show little effect on productivity. Extremely high temperatures have been shown to lower oil percentage, seed fill and germination. Optimum rainfall for growth and productivity is mm. Sunflower is often classified as insensitive to day length, and photoperiod seems to be unimportant in choosing a planting date or production area. 26