Assessing Water Use Efficiency And Water Productivity,and Estimating Evapotranspiration In Maize-soybean Relay Strip Intercropping Systems

Appropriate planting patterns have been shown to promote total yield in maize(Zea mays L.)and soybean[Glycine max(L.)Merr.]relay strip intercropping systems,but whether the changes in planting patterns affect water use efficiency(WUE),water productivity(WP)and crop evapotranspiration(ETc)are unknown.Field experiments were conducted from 2013 to 2015 growing seasons in Renshou county,southwest China,where maize-soybean relay strip intercropping is a dominant cropping system and thus the focus of this study.Maize was planted in the double narrow-row strips,whereas soybean was planted in the double wide-row strips between the maize strips about two months before the maize maturity.Li-6400XT portable photosynthesis system was used to measure leaf transpiration of maize and soybean.In addition,dual leaf model was employed to upscale from leaf-to-plant level transpiration of maize-soybean intercrops.Soil evaporation was measured using microlysimeters.Soil water content at 0-30 cm soil depth was measured gravimetrically,whereas neutron probes were used to measure the changes in soil water at soil depth of 30-100 cm.Home-made circular rain water collectors each with a diameter of 16 cm were used to measure throughfall.Soil conservation services(SCS)runoff model was used to estimate runoff water.Grain yields and land equivalent ratios in maize-soybean intercropping were measured in each growing season.Finally,the crop evapotranspiration(ETc),water use efficiency(WUE),group water use efficiency(GWUE),water capture efficiency(CWATER),water productivity(WP)and water equivalent ratios(WERs)were assessed for different planting patterns of maize-soybean relay strip intercropping.Our results showed that changes in planting patterns had a dominant effect on the canopy structure and coverage of maize plants,thus the SWC.soil evaporation and throughfall followed a decreasing trend in the order:central row of maize strip(MM)<adjacent row between maize-to-soybean strip(MS)<central row of soybean strip(SS).Leaf area index(LAI)of intercropped maize in all treatments was significantly greater than that in sole cropping.With increasing the distance between maize narrow rows,the leaf transpiration of intercropped maize decreased,whereas opposite trend was found for soybean leaf transpiration.Dual leaf model tends to overestimate the leaf transpiration of maize and soybean intercrops.Component yields of maize and the total yield of maize-soybean intercrops increased with increasing the distance between maize narrow rows up to 40 cm,but they gradually declined thereafter.By contrast,the component yield of intercropped soybean declined throughout with increasing the distance between maize narrow rows.Although the component yields of maize and soybean intercrops were lower than their sole crop counterparts,but the total yields in intercropping were significantly higher compared to sole cropping.LER values were not less than 1.52 in all growing seasons from 2013 to 2015,indicating the effective utilization of land by the intercropping.Planting patterns did not show any significant effects on ETc of maize and soybean intercrops.WUEs of maize and soybean intercrops were also lower than that of sole maize or sole soybean;however,the maximum GWUEs and WPs in the planting patterns with 40 cm maize narrow-row spacing were significantly higher compared to sole cropping.Moreover,the highest WER values(1.79 in 2013 and 1.76 in 2014)in the planting patterns with 40 cm maize narrow-row spacing,indicating the water use advantage of intercropping.From our results,we conclude that maize narrow-row spacing of 40 cm and soybean wide-row spacing of 160 cm(200 cm bandwidth;2:2 maize-to-soybean rows)could be the viable planting pattern management method to reduce soil water losses,and gain high GWUE and WP in maize-soybean relay intercropping systems.