Co-implementation of tillage, irrigation, and fertilizers in soybean: Impact on crop productivity, soil moisture, and soil microbial dynamics

Due to depleting water supplies and the cultivation of high water-demanding crops like rice, water deficit in crop production has become a major concern, especially in semi-arid regions of South Asia. Soybean has been considered a possible substitution for high-water-demand crops with improved water productivity and nutrient quality. However, due to inefficient and injudicious water and fertilizer management, the overall productivity and profitability of soybean is quite low. Hence, a three-year field investigation was carried out using strip-strip plot design with three replications to study the individual and combined effects of tillage, irrigation, and fer-tilizer levels on crop yield and quality, soil moisture and soil microbial dynamics. Results revealed that zero tilled-flat beds (ZTFB) and conventional tilled-raised beds (CTRB) reduced the irrigation water requirement by 5.15-5.45 and 3.12-3.49 cm ha-1, respectively, compared to conventional tilled-flat beds (CTFB). Moreover, CTRB enhanced seed yield by 8.1-31.5 %, biomass yield by 6.5-34.1 %, crop water productivity (CWP) by 27.2-30.9 %, and irrigation water productivity (IWP) by 55.2-57.5 % over CTFB. Similarly, in 2016 and 2017, CTRB had higher SPAD-chlorophyll content (34.3 and 33.2 in the top leaves) and normalized difference vege-tation index (NDVI) (0.51 and 0.71) values than CTFB and ZTFB. At 0.0-0.30 m soil depth, ZTFB showed the highest soil moisture content of 11.2 % and 22.5 %, respectively, leading to the highest relative water content (RWC) of 76.7-78.7 % in soybean leaves. As a result, ZTFB took 4-8 days longer to mature than CTFB, delaying the sowing of the following wheat crop. During the 2016-2018 growing seasons, irrigation applied at the depletion of available soil moisture (DASM) by 25 % and 100 % rate of recommended fertilizer (RRF) achieved significantly higher crop, biomass yields, protein yield, SPAD, NDVI, and CWP than irrigation at lower levels. Interaction effects revealed that combinations of CTRB and ZTFB + 25 % DASM + 100 % RRF strategies generated significantly (P <= 0.05) higher seed yield, biomass yield, and CWP. At the same time, ZTFB had significantly higher alkaline and acid phosphatase activity than CTRB, whereas the latter had significantly higher soil microbial biomass carbon. In comparison to individual use of these crop management methods, the results of this study showed planning soybean either in CTRB or ZTFB, irrigating at 25 % DASM, and fertilizing crops with 100 % RRF could help achieve higher crop and water productivity, thus sustaining soybean production in India and adjoining regions with similar agro-ecology.

Automated summary

This study investigated the effects of tillage, irrigation, and fertilizer levels on soybean yield and quality, soil moisture, and soil microbial dynamics. The results showed that conventional tilled-raised beds reduced irrigation water requirement and improved soybean productivity and nutrient quality. Planning soybean in conventional tilled-raised beds or zero tilled-flat beds, irrigating at 25% depletion of available soil moisture, and fertilizing crops with 100% recommended fertilizer rate could help achieve higher crop and water productivity.