<i>Effects of fertilizer application rates for key growing stages on maize growth and yield in sub-humid Northeast China</i>

In order to explore the effects of fertilizer application rate for key growing stages (jointing stage, heading stage and filling stage) on plant height, leaf area index (LAI), aboveground plant biomass, nitrogen uptake, nitrogen use efficiency and grain yield of maize under drip irrigation, a one-year field experiment in the semi-humid region of Northeast China was conducted at various fertilizer levels in key growing stages. Three fertilizer ratio (jointing stage: heading stage: filling stage) treatments, including uniform fertilizer rate in each stage (T1, 1:1:1), lower rate in heading stage (T2, 2:1:2) and higher rate in heading stage (T3, 3:6:1) were tested. The results showed that the fertilizer ratio significantly affected plant height at the middle and later periods, and had insignificant effects on LAI throughout the growing season. Higher rate in heading stage (T3) generally produced lower plant height, attributing to the fertilizer control at the jointing stage. Although no significant differences of aboveground plant biomass, nitrogen uptake and fertilizer-N use efficiency were found for all treatments, T3 obviously produced higher aboveground plant biomass and N accumulation, and thus effectively promote the fertilizer-N use efficiency by 5.5-7.2%. In terms of yield and yield components, there was no statistical significance in ear length, barren ear tip, kernel number per cob, 100-seed weight and grain yield among various treatments. Meanwhile, higher grain yield were generally found in T3, of which grain yield was 1.3-4.6% higher than that of T1 and T2, thereby improved the productivity of N fertilizer. In conclusion, the optimum fertilizer application rates should be higher rate for jointing and heading stage and lower rate for filling stage in the sub-humid Northeast China.