Variations of the grain yields and N absorption of spring maize in Heilongjiang Province

【Objectives】In high-yield maize production system, the overestimation of nitrogen (N) requirement resultes in the overuse of N fertilizer and environmental pollution. Maize grown area was increased rapidly in Heilongjiang Province in the past decades. Collecting and analyzing the existed maize trails data is significant for the comprehensive understanding of the relationship between nitrogen (N) requirement and grain yield in Heilongjiang Province. The objectives of this study were to quantify the grain yield-N requirement, evaluate the variation of N requirement with the yield increase, investigate the N requirement charcteristics of maize cultivars with different maturation periods, and the relationship between grain yield-N requirement with different nitrogen fertilization methods. 【Methods】The existing 439 maize yield data from 56 field experiments in Heilongjiang Province from 2003 to 2012 were collected and the relationship between grain yield and the above-ground N uptake at maturity was simulated by linear, quadratic, power and exponential models. A field experiment was conducted with different notirogen fertilizers and different application methods, the yield and nitrogen efficiency were investigated. The best fitting is with the power model.【Results】The production of maize in Heilongjiang province has increased from 8.5 t/ha in the 2000s to 9.7 t/ha in 2010s, and one of the major reasons for the increase was the increased harvest index due to cultivars. The average yield of 56 maize experiments is 9.5 t/ha, higher than the national average of 5.3 t/ha and the world average yield of 4.5 t/ha. The average N absorption for each 100 kg of grain production is 16.7 kg. When the maize yield is defined as 6 levels: 7, 7-8, 8-9, 9-10, 10-11 and 11 t/ha, the N absorption per 100 kg grain yield is 18.3, 18.3, 16.8, 17.0, 16.4 and 15.3 kg respectively. Early mature cultivars usually absorb more nitrogen than the late mature cultivars. When the urea is applied 40% by basal and 60% by top dressing, or 40% of urea N plus 60% of controlled-released urea N are basal applied together, the nitrogen absorption per 100 kg of grain yield is significantly higher than the urea or controlled-release urea was all one-time basal applied. 【Conclusions】The decreased N absorption per tone of grain production is mainly caused by the extention of late maturing cultivars with high harvest index (HI). With those cultivars, the N concentration is diluted by the higher yiled. At the same grain yields, the N conents in grain and straw in the early-maturing varieties are higher than those in the late maturing ones. Application of urea by basal plus top dressing or the combined one-time basal application of 40% of urea plus 60% of controlled-rellease urea could increase the nitrogen harvest efficiency and the yield, so they are worth of recommend method.