| Drip irrigation under plastic film mulch is an alternative that has been applied to maize production in China in recent years.The typical advantages included increasing the topsoil temperature during the early growth stage,reducing evaporation from soil surface,decreasing nitrate leaching and enhancing the yield.However,there are problems such as improper irrigation and fertilization methods in application of drip irrigation systems under plastic film mulch in China.For better understanding of the effects of mulched drip irrigation on water and heat conditions in field and maize yield in sub-humid regions,the effects of mulched drip irrigation on farmland environments,maize growth and yield were evaluated.Moreover,effects of the number of fertigation events and rates on the change of soil nitrate,plant growth,N uptake,and grain yield were also taken into consideration and provide recommendations for developing the best management practices for drip-irrigated maize under mulch in the sub-humid region.Furthermore,quantification of the effects of PFM and irrigation requirements in sub-humid Northeast China during different growth stages under diverse climatic conditions were also studied.Main work and results are as follows:(1)Field experiments were carried out in sub-humid Heilongjiang Province,China,during the growing seasons 2011,2012,and 2013 maize growing seasons.In the experiments,three treatments,mulched drip irrigation,non-mulched drip irrigation,and surface irrigation were tested.The soil water content,soil temperature,soil evaporation,air temperature and humidity in canopy,plant height,leaf index,dry matter aboveground,nitrogen uptake,and maize yield were measured.The results indicated that mulched drip irrigation increased the daily temperature at 5 to 25 cm soil depth by 2.3? compared the non-mulched treatments.Accordingly,the accumulated soil temperature for the mulched drip irrigation treatment was about 115 to 150? higher than that for the non-mulched treatments during the whole growing season.Furthermore,the daily evaporation rate from the soil surface for the mulched irrigation treatment was 53%lower than that for the non-mulched drip irrigation treatment,resulting in higher water content in topsoil layer during the early growing season.Compared to the non-mulched irrigation treatment,the mulched drip irrigation produced a higher air temperature and lower air in canopy at sunny days of the jointing stage.In terms of crop growth,the growth speed of plant height,LAI,dry matter aboveground and nitrogen uptake with the growing degree days above 10? for the mulched drip irrigation treatment was obviously greater than that for the non-mulched drip irrigation surface irrigation treatments during the early growing stage.At maturity stage,the dry matter aboveground averaged over the three growing seasons for the mulched drip irrigation treatment was and 23%greater than that for the non-mulched drip irrigation and surface irrigation treatments,respectively.Accordingly,the nitrogen uptake for the mulched drip irrigation treatment was 16%and greater than that for the non-mulched drip irrigation and surface irrigation treatments,respectively.The 3-year average grain yield and water use efficiency for the mulched drip irrigation treatment was 11%8%greater than that for the non-mulched drip irrigation treatment,and 21%and 18%greater than that surface irrigation treatment,respectively.(2)Field experiments were conducted to investigate the influence of fertigation splits and rates on the nitrate content in the soil,plant growth,nitrogen uptake,and grain yield during the maize growing seasons in 2011,2012,and 2013.The experiments used a single early-season fertigation and three in-season split fertigation events.For each fertigation treatment,four nitrogen levels of 50,100,150,and 200 kg hm-2 were tested using a randomized complete block design with three replicates.The results indicated that,for a given amount of nitrogen applied,the split fertigation treatments increased the nitrate content in the root zone during the late growing season,reducing the fluctuation of nitrate content in soil during the growing season.The effect of nitrogen splits on maize growth and yield was statistically significant.The single nitrogen application significantly increased the plant height,LAI,dry matter aboveground and nitrogen uptake of maize in the early growing season.However,the three nitrogen splits in season produced a higher dry matter aboveground and nitrogen uptake in the late growing season.The yield averaged over the three nitrogen splits treatments was nearly 5%greater than the single nitrogen application treatments.The nitrogen rates had an insignificant effect on plant height and LAI during the whole growing season,but had a positive effect on dry matter aboveground and nitrogen uptake,especially in the late growing season.Corn yield demonstrated a linearly increasing trend with the amount of nitrogen applied.We recommended a management practice of 150?200 kg hm-2 of in-season nitrogen applied at three nitrogen splits with plant densities of 46620 plants ha-1 to obtain high production while reducing the risk of nitrogen leaching in sub-humid Northeast China.(3)The Hybrid-Maize model was added the heating effects of plastic film mulching on rising surface-soil temperature and decreasing soil evaporation and then calibrated and applied in a sub-humid Northeast China to quantify effects of plastic film mulching on grain yield and water use efficiency under irrigated scenarios.And the Hybrid-Maize model was also applied to estimate irrigation requirements for drip-irrigated maize during different crop physiological development stages and under diverse agro-climatic conditions.The results indicated that Hybrid-Maize model performed well in simulation of seasonal soil water storage daynamics and in-season aboveground dry matter in three years but overestimated LAI for in 2012 and 2013 for both mulched and non-mulched treatments,and underestimated final aboveground dry matter at maturity in 2011 and 2013 for mulched treatment.Although the model overestimated the grain yield and WUE in 2013 for both treatments,the revised Hybrid-Maize model did still reflect the effects of PFM on increasing grain yield and WUE during the three growing season.In a sub-humid Heilongjiang Province,seasonal irrigation requirements were highly related to initial soil water content and distribution of seasonal precipitation.More than 94%of the maize harvested area in Heilongjiang Province is needed to be irrigated although the yield increase varied(0?109%)in diverse agro-climatic zones.Consequently,14%to 42%of more total maize production could be achieved through drip-irrigation systems compared to rainfed conditions. |
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