Effects of Crop Residue Removal on Soil Water Content and Yield of Deficit-Irrigated Soybean

Reduced tillage, with more crop residue remaining on the soil surface, is believed to conserve water, especially in arid and semi-arid climates. However, the magnitude of water conservation is not clear. An experiment was conducted to study the effect of crop residue removal on soil water content, soil quality, and crop yield at North Platte, Nebraska. The same field plots were planted to soybean (Glycine max) in 2009 and 2010. There were two treatments: residue-covered soil and bare soil. Residue (mostly corn residue in 2009 and mostly soybean residue in 2010) was removed every spring from the same plots using a flail chopper and subsequent hand-raking. The experiment consisted of eight, 12.2 m 12.2 m, plots (two treatments with four replications each). Soybeans were sprinkler-irrigated, but purposely water-stressed, so that any water conservation in the residue-covered plots might translate into higher yields. After four years of residue removal, soil organic matter content and soil residual nitrate nitrogen were significantly smaller, and soil pH was significantly greater, in the bare-soil plots compared to the residue-covered plots. The residue-covered soil held approximately 90 mm more water in the top 1.83 m compared to the bare soil near the end of the 2009 growing season. In addition, mean soybean yield was 4.5 Mg ha-1 in the residue-covered plots, compared to 3.9 Mg ha-1 in the bare-soil plots. Using two crop production functions, it is estimated that between 74 and 91 mm of irrigation water would have been required to produce this extra 0.6 Mg ha-1. In 2010, mean soybean yield was 3.8 Mg ha-1 in the residue-covered plots, compared to 3.3 Mg ha-1 in the bare-soil plots. Between 64 and 79 mm of irrigation water would have been required to produce this extra 0.5 Mg ha-1. In both years, several processes may have contributed to the differences observed: (1) greater evaporation of water from the soil in the bare-soil treatment, and (2) greater transpiration by plants in the bare-soil treatment in the beginning of the growing season as a result of more vegetative growth due to higher soil temperatures in the bare-soil treatment.