Effect of Simulated Plow-sole on Water Uptake and Yield of Dryland Wheat

Yield of dryland crops grown on stored water is determined by water use from the profile which, in turn, is related to the extent of root proliferation in different layers. Plow-soles of high strength may retard root growth and adversely affect crop production. We determined the effect of initial profile water storage and soil compaction below the seed on the growth and the yield of dryland wheat, (Triticum aestivum L.) in field experiments during 1970-71 and 1971-72. Compaction reduced water use from deeper layers and decreased grain yield during both years. Evidently, it retarded root growth through increased soil strength. Compared with lower initial water storage, higher initial water storage in the profile resulted in more vigorous plants, deeper rooting, greater water use from lower soil layers and higher yields. The results suggest that for greatest yields, compact layers below the seed must be loosened by tillage to permit deeper rooting. Also, in the absence of early season rain, a small supplementary irrigation to the young crop may stimulate deeper rooting and increase water use from lower layers. Additional index words: Soil compaction, Rooting pattern, Moisture use, Seeding-time soil water, Dryland wheat production. W precipitation during the growing season is low and supplemental irrigation is not available, crop yields are mainly determined by the 1 Contribution from Department of Soils, Punjab Agricultural University, Ludhiana, India. Received Mar. 21, 1974. -' Professor of Soil Physics, PAU, Ludhiana, Research Associate, ICRISAT Hyderabad, and Soil Science (Extension) Specialist, PAU, Ludhiana, respectively. utilization of water stored in the soil. The amount of stored water that becomes available to the crop is directly proportional to depth of rooting and extent of root proliferation in different soil layers. Factors that reduce root growth would reduce yields in dryland crops by reducing soil-water utilization. Increased soil strength is known to retard root growth (Gill and Miller, 1956; Taylor, Roberson, and Parker, 1967) and to reduce root elongation rates. When the soil strength exceeds a certain threshold value (Zimmerman and Kardos, 1961; Barley, Farrell, and Greacen, 1965; Barley and Greacen, 1967; Taylor and Bruce, 1968), root penetration is retarded. Soil strength is a function of bulk density and soil moisture tension (Taylor and Gardner, 1963). At high soil moisture tension, which usually occurs in the surface layers of unirrigated soils, the soil strength may be considerably increased by a small increase in bulk density. The root growth thus may, be hampered even by mild plow-soles under unirrigated conditions. Much of the research on soil compaction under dryland conditions in the past has been conducted with crop plants which have tap roots. Consequently, there is a great need for more information on crops, such as wheat, (Triticum aestivum L.) which have fibrous root systems. This report describes the results of a 2-year study on the effect of simulated plow-soles and initial profile water storage on the water use and yield of dryland wheat. 370 AGRONOMY JOURNAL, VOL. 67, MAY-JUNE 1975 Table 1. Physical characteristics of the soil from experimental site. ~ofl Textural Bulk Moisture re~ention depth Sand Silt Clay class density 1/3 bar 15 bar cm -~0 -g cm-3 cm 3 cm-3 O15 79 7 14 Saady loam I, 46 O. 140 O, 053 15.55 62 16 22 Loam I, 31 O. 201 O. 091 60 55-105 5l 15 24 Clay loam I. 29 O. 210 O. 094 105-145 65 14 21 Loam i, 27 O. 183 O. 078 145-180 81 7 12 Sandy loam I. 32 O, 109 O. 045 RAINFALL EXPERIMENTAL PROCEDURE Field experiments were conducted on sandy loam soil during 1970-71 and 1971-72. Physical characteristics of the soil profile are given in Table 1. These soils have been developed from alluvium of pleistocene to recent times under ustic moisture regime. Loamy sand to sandy loam at the surface and loam in the subsurface, they belong to the family : fine loamy, hyperthermic, mixed, calcareous, typic ustochrept (Sehgal and Cys, 1970). Treatments included (i) no compaction (Co) and (ii) lated plow-sole created by compaction (C~) at low (W~) high (W2) initial profile water storage obtained by varying the amount of presowing application. Soil water content in different layers under low and high water storage is shown in Table 2. To create plow-sole, the entire surface was compacted at soil water contents shown in Table 2 with the wheels of a 1,700 kg tractor which exerted a pressure of 0.65 kg cm-~. Fresh compaction was done both years. Immediately after compaction wheat was sown in furrows made by a single-row, bullock-drawn indigenous wooden plow having a metallic tip. This operation loosened the approx, upper 8 cm layer and left a slightly dense layer below. After the soil was settled by rain during the growing season soil clods were obtained from 0 to 7.5, 7.5 to 15 and 15 to 22.5 cm layers and their bulk density was determined by the saturation method of Prihar and Hundal (1971). Distribution of bulk density in different treatments is shown in Table 3. Semidwarf wheat, ’Kalyan 227{ was planted in 30 cm wide rows iu l0 X 3 m plots in five replicates on Nov. 30, 1970 and in 22.5-cm rows in 10 )< 3 m plots in six replicates on Nov. 24, 1971. Calcium ammonium nitrate and superphosphate to supply 45 kg N + 45 kg PzO~ ~nd 50 kg N + 30 kg P~O~/ha were drilled below the seed during 1970-71 and 1971-72, respectively. Crop was harvested in the first week of May during both years. In addition to measuring grain and straw, plant height, grains per spike, and 1,000 grain weight were recorded. Cumulative rainfall and evaporation h-om U.S. Weather Bureau Class A Pan for the two growing seasons are shown in Fig. 1. Soil moisture content was determined periodically in 0 to 15, 15 to ~0, 30 to 60, 60 to 90, 90 to 120, 120 to 150 and 150 to 180-cm layers in three replications except at harvest, when the sampling could be done in two replications only.