Water productivity in soybean following a cover crop in a humid environment

We evaluated the influence of the termination dates of a winter cover crop on (i) soil water availability during soybean (Glycine max L. (Merr)) growing season, (ii) soybean evapotranspiration (ET) and iii) water productivity in soybean (WP = Grain yield/ET) in a humid environment (i.e., 50 % of years with annual rainfall >= 900 mm). Experiments were carried out at Balcarce, Argentina during two growing seasons. Treatments included (i) soybean monoculture, (ii) soybean following a cover crop with an early termination date, and (iii) soybean following a cover crop with a delayed termination date (similar to 25 days later than the early one). Oat (Avena sativa L.) was used as a cover crop. Soil water content was measured with a neutron probe from cover crop sowing to soybean physiological maturity, and soybean ET was calculated by means of a soil water balance. Cover crop shoot biomass was determined immediately before termination dates and soybean grain yield was quantified at physiological maturity. Cover crops reduced soil available water (SAW) at cover crops termination date from 18 to 23mm at early and delayed termination dates, respectively; and reductions were mostly evident in the upper 40 cm of the soil profile. Termination delays of around 25 days increased 60 % cover crops shoot biomass production, and promoted larger SAW reductions at termination date. However, cover crops had little impact on SAW during soybean growing season and they did not influence soybean grain yield. Moreover, our findings evidenced that in this humid environment (i) soybean ET was reduced between 12 and 17mm following a cover crop, (ii) larger soybean ET reductions were associated with larger cover crops shoot biomass production, and (iii) WP in soybean was slightly improved (4-10%) by the inclusion of a cover crop.