Vietnam soils. Soil K and soil P status. Rich in phosphorus >0.10% P 2 O 5. in hydromorphous soils >0.20% P 2. in ferralitic soils

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Paula Briggs
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% P O in ferralitic soils Medium in phosphorus >0.0 0.

1 Vietnam soils K and soil P status Rich in phosphorus >0.0% P O in hydromorphous soils >0.% P O in ferralitic soils Medium in phosphorus > % P O in hydromorphous soils >0.0 0.% P O in ferralitic soils Poor in phosphorus <0.0% P O in hydromorphous soils <0.0% P O in ferralitic soils Rocky mountains

2 Vietnam: major soil s and distribution Haplic Arenosols Ustipsamments Haplic Arenosols Ustipsamments Salic Fluvisols Hydraquents Orthithionic Fluvisols Sulfaquepts Eutric Fluvisols Udifluvents Cambic Fluvisols Udifluvents FAO-UNESCO USDA ( Taxonomy)

3 Vietnam: major soil s and distribution Haplic Acrisols Hapludults Calcic Luvisols Paleustalfs Rhodic Ferralsols Haplustox Xanthic Ferralsols Hapludox Haplic Acrisols Kanhapludults Haplic Acrisols Haplustults

5 An introduction to the major soil s in Vietnam Vietnam has an estimated cultivable soil base of. M ha. Approximately. Mha (%) is presently used for agriculture. Another. M ha (%) is covered by forest vegetation. s Ferralitic soils (. Mha) are the most commonly occurring soil. They are derived from a variety of parent materials (e.g. metamorphic and igneous rocks, sandstone, clay-shale, old alluvium sediment) and cover large areas on Vietnam s mountainous regions. These soils are mostly acid and have low soil fertility status (Table -). Red soils (. Mha), together with ferralitic soils, provide the main potential land reserve for the expansion of perennial upland crops. At present the alluvial soils of Vietnam s river basins (. Mha) are occupied largely by lowland annual cropping systems, as are the marine sandy soils of the coastal areas (0. Mha) and the gley soils (0. Mha) of North and North Central Vietnam. Agricultural potential The potential for expansion of lowland systems lies in the areas occupied by acid sulfate soils (. M ha) and saline soils ( M ha). In order for successful cultivation of agricultural crops, however, planned amelioration efforts are necessary on these soils. Based on topsoil characteristics, % of Vietnam s cultivable soils are acid (ph KCl <.). Other limitations of Vietnam s potentially cultivable soils include: Very low organic matter content in M ha (%); Very low contents of total P in. M ha (%); Very low to low contents of available P in. M ha (%); Rather low K reserves on. M ha (%); and Very low to low available K contents in. M ha (%) of the cultivable soil base of total. M ha (Table -; see also Table -).

6 Table - Area, distribution and selected characteristics of major soils in Vietnam. # group/typ e Area, 000 h a Occurrence/ Distribution Sandy soils 0 0 Coastal areas o f Central Vietnam S aline soils,00 0 Coastal areas of Nort h & South Vietnam Acid sulfate soils,0 0 and Red Rive r Mekong Deltas A lluvial soils,0 0 asins of the river s Gley soils 0 0 North & North o f Ferralitic & gre y degraded soils p H l B 0 Central Vietnam,00 Midlands of North & Southeast Vietnam Grey plinthic soils 0 Midlands of North & Southeast Vietnam G rey gleyic soils 0 0 Midlands of North & Southeast Vietnam Ferralitic soils n,00 Throughout mountain clay shale & areas matomorphic rocks 0 Ferralitic soils derived from acid igneous rocks Ferralitic soils derived from sandstones Ferralitic soils derived from old alluvium,00 Mountainous areas o f North & Central Vietnam,00 Northeast & Centra l Vietnam 00 Bac Giang, Bac Kam, Thai Nguyen, Vinh Phuc, Phu Tho, Ha Tay Textur Total OM C lay S il t S an d N P K % % % e K C CEC c mol kg.-. < 0- > i -

7 CEC c mol kg Textur Total OM C lay S il t S an d N P K % % % The BALCROP project was initiated in. During Phases I and II of this project, experiments were carried out on the representative soil s found in the major agricultural regions of Vietnam. The representative topsoils were identified as follows: No : Representing the alluvial soils of the Red River Delta; No. : Representing the alluvial soils of the Thai Binh River; No. 0: Representing the degraded soils of the Northern Midlands; No. : Representing the yellow red (ferralitic) soils of the Northern Midlands; No. : Representing the marine sandy soils of the coastal areas; No. : Representing the basaltic red brown soils of the Central Highlands; No. : Representing the grey soils of the Southern North East region; No. : Representing the alluvial soils of the Mekong River Delta; No. : Representing the acid sulfate soils of the South. No. : Representing the acid sulfate soils of the North. Table - continued. # group/typ e p H l Occurrence/ Distribution Area e K C Red soils derive d, 000 h a - from basic igneous rocks ,00 Central High Plateau, Southeast & Northwest Vietnam, Nghe An, Quang Tri Red soils derive d from lime stones Northwest & Northeas t Vietnam, Ninh Binh, Than Hoa, NgheAn, Quang Binh,00

8 characteristics Physical characteristics Alluvial soils (No., and ) are characterized by large amounts of clay (> 0%), small amounts of sand (~ 0%), and medium high contents of organic carbon. Marine sandy soils (No. ) have the largest sand content (> 0%) and, as with most of the degraded soils, are distinguishable by a relatively small clay content and also small organic carbon content. Highland soils (No. ) have loamy textures and high organic carbon content. The largest accumulation of organic carbon (> %) is found in the acid sulfate soils (No. ) of the Mekong River, which is caused by poor aeration due to a water table that is permanently high (Figure - ). Sand Silt Clay 0 C org (%) per cent per cent Figure - texture and organic carbon content in selected topsoils of Vietnam.

9 Chemical properties In accordance with their larger clay and organic matter contents, alluvial soils are generally characterized by a high cation exchange capacity (CEC) of > cmol kg -, while the more sandy degraded soils have lower CEC s. On most of the degraded and upland soils, the CEC is below the critical of cmol kg - (Figure -). The two acid sulfate soils are classified as very acid (ph <.). With the exception of alluvial soil No. (ph > ) and marine sandy soils No. (ph = ), s for ph-water are <. in all other soils, and <. in of the soils (Figure -) CEC (cmol kg - ) ph Figure - Cation exchange capacity (CEC) and ph KCl in selected topsoils of Vietnam.

10 The majority of the selected topsoils are deficient in N and available P. Nitrogen contents in the alluvial soils of the North are unexpectedly low, while available P extends beyond the critical of mg P kg - in only two of the alluvial soils (Figure ). Phosphorus s of > mg P kg - are found only in two degraded soils. The small s in some of the degraded and upland soils (No.,,, ) indicate severe P deficiency (Figure -). Exchangeable calcium contents are high in the alluvial soils of the North and South. In most of the degraded (No.,,, ) and upland soils (No.,,, ), however, they were generally found to be low and in some cases very low (< 0.0 cmol kg - ). Exchangeable K s for all soils, with the exception of No.,, are below the critical of 0. cmol kg - (Figure -). The exception, on the red-brown basaltic soil of the Dak Lak province grown to coffee (No. ), can likely be explained by large fertilizer K inputs. When used under conditions of intensified cropping, none of the other soils will meet crop requirements of K (although K reserves, particularly in the alluvial soils, may be sufficient to support smaller crop yields). Exchangeable Mg is above the critical (0. cmol kg - ) in the alluvial soils of the North and the South (Figure -). All degraded and upland soils, however, have rather low contents of exchangeable Mg, indicating that on these soils, Mg is next in line (after K, P, and N) in limiting agricultural production in Vietnam. As expected, the acid sulfate soils (No., ) are extremely rich in S. Most other soils contain at least mg S kg - (Figure -) Available N (mg kg - ) Available P (mg kg - ) Figure - Available nitrogen and available phosphorus content in selected topsoils of Vietnam.

11 Exchangeable Ca (cmol kg - ) Exchangeable K (cmol kg - ) Figure - Exchangeable calcium and exchangeable potassium content in selected topsoils of Vietnam Exchangeable Mg (cmol kg - ) S (mg kg - ) Figure - Exchangeable magnesium and sulfur content in selected topsoils of Vietnam.

12 Zn (mg kg - ) Cu (mg kg - ) Figure - Zinc and copper content in selected topsoils of Vietnam. Among the micronutrients analyzed, Zn is below the critical of. mg kg - in of the topsoils (Figure -). The low s in four of the six alluvial soils indicate that Zn deficiency may be limiting the productivity of rice-based systems in these generally more fertile soils. Copper contents in these soils are generally high but some of the degraded soils (e.g. No.,, ) have Cu contents below the critical of. mg Cu kg - (Figure -). The red brown basaltic soils of the Central Highlands (No.,, ) contain ~0. mg B kg - and are likely to be B-deficient. B in some of the degraded soils (No.,, ) is also found below the critical of 0. m B kg - while all the other topsoils appear to be sufficiently supplied with boron (Figure -). All degraded soils, marine sandy soil (No. ), grey soil (No. ) and acid sulfate soils (No., ) have small contents of Mn (< mg Mn kg - ). Red-brown soils of the Central Highlands (No. ) and alluvial soils appear to be well supplied with manganese (Figure -).

13 B (mg kg - ) Mn (mg kg - ) Figure - Boron and manganese content in selected topsoils of Vietnam. Conclusions We can conclude, from the analytical results of the topsoils selected to represent major cultivated soils of Vietnam, that sustainable crop production at high yield levels is limited by the following general constraints: Alluvial soils These naturally fertile soils require extra N, P, and K supply in intensified cropping systems (> harvest p.a.) in order to sustain large yields. Degraded soils These generally low fertility soils rely on organic matter in order to improve nutrient and water retention. In addition to FYM and green manure, judicious use of manufactured fertilizer N, P, K, Mg, Ca, and S nutrient sources is required. In some cases, extra Zn, Cu, B and Mn supply is required. Coastal soils The sandy marine soils of the coastal areas of Vietnam are generally of low fertility status. Crop cultivation here is limited by small contents of organic matter and deficiency of macro- and micronutrients, as well as the extended dry and wet situations under the influence of typhoons and hot winds. Highland soils The loamy soils of basaltic origin in the plateau regions of the Central and Western Highlands are generally deep and well structured. If supplied with fertilizer nutrients, especially P, K, Ca, and Mg, and supported by irrigation during dry periods, these soils will be among the most productive upland soils of Vietnam and are known to sustain large yields of perennial crops (coffee, fruit trees, rubber) and annual crops (maize, vegetables, cassava).

Soils of Palau. Diversity and Fertility. Palau Livestock Management Workshop March 23-25, Jonathan Deenik, PhD University of Hawaii

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