The Combined Effects of Groundwater Depth and Nitrogen Fertilization on Yield of Summer Maize and Nitrate Distribution in Soil

Abstract

【Objective】 Soil water and nutrients combine to impact crop growth and nitrogen cycling. The objective of this paper is to study how groundwater depth and nitrogen fertilization modulate yield and nitrogen use efficiency of summer maize, as well as its consequent impact on nitrate dynamics. 【Method】 The experiments were conducted in lysimeters under different combinations of groundwater depth and nitrogen application. We compared three groundwater depths: 2.0 m (G1), 3.0 m (G2) and 4.0 m (G3); on top of these were two nitrogen treatments: conventional nitrogen fertilization used by local farmers (N2), and reducing it by 20% (N1), with no nitrogen fertilization and water control as control (WN). During the experiment, we measured the growth traits of the summer maize and nitrate dynamics in soil in each treatment. 【Result】 The leaf area index (LAI) was affected by groundwater depth but peaked at the grouting stage in all treatments. When nitrogen application was the same, LAI in G1 at mature stage was higher than that in G2 and G3 at a significant level. When groundwater depth was the same, increasing nitrogen application boosted LAI at mature stage. When nitrogen was applied at conventional level, the number of days that maize saw a rapid growth in G1 was 3.99% and 12.91% longer than that in G2 and G3, while its associated growth rate reduced by 9.69% and 14.65% respectively; G3 gave the highest yield. Reducing nitrogen application reduced the yield in G2 and G3 more significantly than in G1 due to the reduction in rapid-growth duration. Keeping nitrogen application at conventional level in G1 increased soil NO3- in top 20 cm of soil by 75.92% and 90.03%, and in 20~40 cm of soil by 30.56% and 130.95%, respectively, compared with that in G2 and G3. Reducing nitrogen application by 20% increased the grain yield per plant by 9.13% at significant level. Pearson correlation analysis showed that when nitrogen was applied at the conventional level, nitrate in 0~40 cm of soil varied with groundwater depth and was negatively correlated with the yield with R2 varying from 0.827 to 0.883. 【Conclusion】 High nitrogen fertilization and shallow groundwater facilitated vegetative growth, but was unfavorable for reproductive growth thereby reducing the yield of the summer maize. Reducing nitrogen application coupled with shallowing the groundwater will benefit both yield and nitrogen use efficiency.

Keywords

• groundwater table depth
• nitrogen application reduction
• dry biomass matter
• nitrate
• logistic
• yield