IRRIGATION CONTROL IN SUGARCANE FIELD BASED ON NEUTRON PROBE MEASUREMENTS

Transcription

1 Agronomy - RRGATON CONTROL N SUGARCANE FELD BASED ON NEUTRON PROBE MEASUREMENTS H Y.S. Sheu and P.C. Yang Taiwan Sugar Research nstitute, Tainan, Taiwan, Republic of China ABSTRACT Studies were conducted on cane growing in clay loam and sandy loam soils using the neutron probe moisture meter. The results showed that the water consumption patterns measured with the meter were rationally related to the cane root distribution, and could be used as a guide in scheduling irrigation. Coh/clusions are that frequent but light irrigations are indicated for ratoon cane and for cane varieties with shallow root systems to avoid water stress during boom stage. However, less irequent irrigations at relatively heavier rates was more suitable for varieties with extensive and deeper root systems. NTRODUCTON n arid and semi-arid regions and most of the time in humid areas with distinct wet and dry seasons, water supplies have to be properly regulated. Accurate determination of the optimum time to apply supplementary water is of prime importance in attaining economies both in water use and cost of production. This is especially important in Taiwan, where the sub-tropical climate is characterised by a very clear wet season from May to September and a dry season from October to next April. n order to make the most efficient use of irrigation water, questions of when to irrigate and how much water is required become the vital concern of plantation managers. Early scientific methods of irrigation control for sugarcane were based on soil moisture measurement^^,^. Recently, however, the meterological approach to irrigation control has been adopted and the U.S. Weather Bureau Class A Pan is now most commonly used to assess crop water requirement^^^^^^. Because the consumption of soil water is dependent not only on the conditions of soil and climate, but also on the kind, stage and condition of the crop, various methods have been used to devise the proper irrigation program, but none of them has proved satisfactory in practice. This paper proposes that neutron probe data which reflect water consumption at various depths in the root zone of sugarcane provide reliable information on which to base an irrigation program. The decline in ratoon yields on TSC plantations in the latest decade has been attributed to several factors, such as soil insect' damage, soil compaction by mechanical harvesting, poor drainage, insufficient irrigation water and improper Keywords: Neutron scattering method, water consumption pattern, root distribution, pan ratio, soil water management,-irrigation control 62

2 Y,S. SHEU AND P.C. YANG 63 management. n this study, the soil water consumption pattern of ratoon cane roots was measured with a neutron moisture meter and the soil water consumption patterns of different varieties were determined. MATERALS AND METHODS Two sets of field experiments were conducted at Taiwan Sugar Research nstitute (TSR) Farm in Tainan. Experiment 1 was carried out on clay loam soil to study the difference in water consumption patterns between spring planted- and ratoon cane. Cane variety F176 was planted on October 3, 1979, and harvested on February 21, Then, half the plots were processed for ratooning and the other half for spring planting. Both canes were harvested on February 25, During the boom stage of growth, the water consumption pattern and root distribution of both canes were investigated for comparison. The data on soil water depletion by sugarcane were measured with a Depth Moisture Gauge (Troxler Model 1255). Each of eight aluminum access tubes were installed down to a 120-cm depth, 10 cm apart from the cane stool for plots of spring and ratoon canes. Three days after irrigation, the neutron probe datawere recorded each 10 cm along vertical profiles, the first measurement being done 10 cm below the soil surface. Meanwhile, numbers of tillers and rates of growth of stalks were measured at monthly intervals. Experiment 2 was conducted on sandy loam soil to study the varietal difference in water consumption. The experiment was laid out in a split plot design with four replications, using different moisture regimes (irrigation control based on pan ratios, PR 0, 0.4 and 0.75) as whole plots and varieties (ROC3, ROC6, ROC7 and ROC8) as small plots. Each plot consisted of six rows, spaced 1.25 m apart, and 8 m long. Sugarcane was planted on October 9, 1981, and harvested on January 22, The data on root distribution and use of soil water were obtained by the same methods as in experiment 1. RESULTS Experiment 1 - Spring plant and ratoon cane Growth pattern - The monthly changes in tillering shown in Figure 1 indicated a big difference between plant and ratoon canes in the early stages of growth but at boom stage, the difference became negligible. However, the stalk elongation patterns were different from those of tillering; as shown in Figure 2. The rate of elongation of the stalks of ratoon cane was greater than that of the plant cane during the early stages but the growth of the plant cane exceeded that of the ratoon cane during the boom stage. Soil water consumption pattern - The neutron probe data measured after irrigation during the boom stage showed large difference in water extraction between plant and ratoon cane. As shown in Figure 3, the top 30 cm layer of soil dried faster in ratoon fields than in plant fields. The water consumption patterns shown in Figure 4 also indicated that the roots of plant cane extracted water from soil layers much deeper than did ratoon cane. Root distribution - Figure 5 shows that plant cane developed a deeper root system

3 64 AGRONOMY than ratoon cane; the roots of the latter were mainly concentrated in the to^ soil layer and only a few roots extended deeper. / - spring cane Ratoon cane 0 A Apr May June July Aug. Feb Date FGURE 1. Changes in number of tillers of spring plant and ratoon cane

4 FGURE 3. Changes in soil moisture profiles of spring plant and ratoon cane (* indicates days after irrigation) Spring cane Ratoon cane FGURE 4. Soil water consumption patterns of spring plant and ratoon cane during growth stage

5 Dry wt. = g Dry wt. = g FGURE 5. Distribution of sugarcane roots (at age 6 months) 1 Experiment 2 - Autumn cane Soil water consumption patterns - Using the neutron moisture meter, the soil water extracted by roots and the consumption patterns of varieties ROC3, ROC6, ROC7 and ROC8 during boom stage were measured, as shown in Figure 6. The results indicated that soil water was extracted markedly in the top 30 cm of soil by varieties ROC7 and ROC3. On the other hand, ROC6 and ROC8 had a tendency to extract more water from the deeper layers. Root distribution patterns - The root distributions of varieties ROC3, ROC6, ROC5 and ROC8 are shown in Figure 7. The data revealed that the roots of ROC7 were more concentrated in the top soil, which resulted in a shallower root zone. On the other hand, ROC6 and ROC8 had more roots penetrated into deeper soil layers. Growth response to soil moisture - Varieties ROC3, ROC6, ROC7 and ROC8 were tested under three different irrigation treatments, PR 0,0.4 and Results (Figure 8) indicated that the response of cane growth to soil moisture was greater for ROC3 and ROC7 than for ROC6 and ROC8. n other words, the effect of soil moisture stress on cane growth was more severe for ROC3 and ROC7. DSCUSSONS AND CONCLUSlONS n recent years, the neutron scattering method has gained widespread acceptance for monitoring water profiles in the field. t allows rapidly and periodically repeated measurements, in the same locations and depths, of the volumetric wetness of a large representative volume of soi13~4,11~12. Hence, this method may be used effectively to measure the continuous changes in soil water content caused by root extraction. The results of this study indicated that water consumption patterns obtained from neutron probe data had appreciable relation to the cane root systems (Figures 4, 5, 6 and 7). Since the water absorption ability is closely related to the root activity, the root distribution profile does not effectively represent the actual absorption in different soil layer^^,^,'^. On the other hand, the soil water consumption pattern derived from the neutron probe data can reveal the actual absorption by roots completely. Therefore, the use of the Depth Moisture Gauge to obtain the water consumption pattern of sugarcane is effective in controlling irrigation.

6 u ROC 7 ROC 3 ROC 6 ROC 8 FGURE 6. Comparison of % moisture extraction from upper and lower soil profiles by sugarcane roots Sampling Profile ROC 7 ROC 3 ROC 6 ROC 8 (% by wt.) FGURE 7. Distribution of sugarcane roots (8-months age) According to the results of this study, recommendations concerning soil water management in cane fields are made as follows: 1. Since the water uptake by ratoon cane roots was more concentrated in the top soil (Figures 3 and 4), unless the physical conditions of the subsoil can be improved in favour of root development, the water stress will occur in the boom stage of ratoon-cane. Hence, light irrigations at frequent intervals are suggested for ratoon cane to avoid water stress during the boom stage of growth. 2. The growth responses of sugarcane vary with variety (Figure 8). n the interests of irrigation efficiency, frequent light irrigations are recommended for varieties

7 67 ROC 3 ROC 6 ROC 8 URE 6. Comparison of % moisture extraction from upper and lower soil prof~les by sugarcane roots Sampling Prof ~ le ROC 7 ROC 3 ROC 6 ROC 8 (% by wt.) FGURE 7. Distribution of sugarcane roots (8-months age) According to the results of this study, recommendations concerning soil water management in cane fields are made as follows: 1. Since the water uptake by ratoon cane roots was more concentrated in the top soil (Figures 3 and 4), unless the physical conditions of the subsoil can be improved in favour of root development, the water stress will occur in the boom stage of ratoon.cane. Hence, light irrigations at frequent intervals are suggested for ratoon cane to avoid water stress during the boom stage of growth. 2. The growth responses of sugarcane vary with variety (Figure 8). n the interests of irrigation efficiency, frequent light irrigations are recommended for varieties

8

9 Y.S. SHEU AND P.C. YANG 69 with shallow root systems such as those of varieties ROC3 and ROC7. On the contrary, less frequent irrigation at a relatively heavier rate is more suitable for varieties with extensive and deeper root systems such as those of ROC6 and 3. Neutron probe data for consumption of water by cane roots are valuable as a guide for better water management in sugarcane fields, especially in relation to newly released varieties in commercial cultivation. REFERENCES 1. Chang, Hao, Wang, J.S: and Ho, F.W. (1968). The effect of different pan ratio for controlling irrigation of sugarcane in Taiwan. Proc. 13th Congr. SSCT Cornelison, A.H. and Humbert, R.P. (1960). rrigation interval control in the Hawaiian Sugar ndustry. Hawaiian Planters' Rec. 55: Gardner, W. and Kirkham, D. (1952). Determination of soil moisture by neutron scattering. Soil Sci. 73: Haverkamp, R., Vauclin, M. and Vachaud, G. (1984). Error analysis in estimating soil water content from neutron probe measurement: 1. Local standpoint. 137(2): Jones, C.A. (1980). A review of evapotranspiration studies in irrigated sugarcane in Hawaii. Hawaiian Planters' Rec. 59: McCoy, E.L., Boersma, L., Ungs, M.L. and Akratanakul, S. (1984). Toward understanding soil water uptake by plant roots. Soil Sci. 137(2): Richards, S.J. and March, A.W. (1961). rrigation based on soil suction measurements. Soil Sci. Soc. Am. Proc. 25: Robinson, F.E., Campbell, R.B. and Chang, Jen-Fu (1963). Assessing the utility of pan evaporation for controlling irrigation of sugarcane in Hawaii. Agron. J. 55(5): Stone, R.L., Teare,.D., Nickell, C.D. and Mayaki, W.C. (1976). Soybean root development and soil water depletion. Agron. J. 68: Taylor, H.M. and Klepper, B. (1973). Rooting density and water extraction patterns for corn. Agron. J. 65: Vauclin, M., Haverkamp, R. and Vachaud, G. (1984). Error analysis in estimating soil water content from neutron probe measurements: 2. Spatial standpoint. Soil Sci. 137(3): Visvalingam, M. and Tandy, J.D. (1972). The neutron method for measuring soil moisture content - A review. J. Soil Sci. 23: