ABSTRACT

Non-optimal nitrogen (N) fertilizer application is frequently caused by a producer’s uncertainty in projecting the N rate that ensures maximum economic return. In order to determine the optimal N rates for maximum and economical yields, the response of maize (Zea mays L.) grain yields to N fertilizer at different rates of compost were evaluated in a calcareous soil. The treatments comprised four compost levels of 0, 20, 40, and 60 m³ ha⁻¹. The N rates were 0, 70, 140, 210, 280, and 350 kg N ha⁻¹ in three equal split doses. Quadratic response functions were observed when maize grain yields were plotted against N fertilizer rates. According to derivative analysis of the functions averaged across the two seasons, grain yield plateaued at 8189 kg ha⁻¹ with an N fertilizer rate of 282 kg ha⁻¹. When the N fertilizer cost to grain price ratio was taken into account, the average economic grain yield was 8077 kg ha⁻¹ by N fertilizer rate of 248 kg ha⁻¹. Numerous future scenarios of fertilizer cost to grain price ratios were assumed in order to determine the economically optimal N rates. The scenario of increasing N fertilizer cost by 40% resulted in a decrease in economic optimal N rate by an average of 15.8 kg N ha⁻¹. However, a 40% increase in grain price resulted in an increase in the economic optimal N rate by 9.4 kg N ha⁻¹. Due to the high N losses in calcareous soils, increasing the N fertilizer cost scenario is beneficial since it decreases the economically optimal rates, which increases N use efficiency while also decreasing reactive N losses and protecting the environment.

摘要

非最佳氮 (N) 肥料施用通常是由于生产者在预测确保最大经济回报的 N 率时的不确定性。为了确定最大和经济产量的最佳氮肥用量，在石灰质土壤中评估了不同堆肥用量下玉米 ( Zea mays L.) 谷物产量对氮肥的响应。处理包括0、20、40和60 m ³ ha ^-1的四种堆肥水平。N 比率为 0、70、140、210、280 和 350 kg N ha ^-1在三个相等的分割剂量。当玉米籽粒产量与氮肥用量作图时，观察到二次响应函数。根据对两个季节平均函数的导数分析，粮食产量稳定在 8189 kg ha ^-1，氮肥施用量为 282 kg ha ^-1。考虑到氮肥成本与粮价比，按248 kg ha -1 的氮肥用量计算，平均经济粮食产量为8077 ^kg ha ^-1。为了确定经济上最佳的氮肥比例，假设了许多未来的肥料成本与谷物价格比率的情景。氮肥成本增加 40% 的情景导致经济最佳氮肥用量平均减少 15.8 kg N ha ^-1. 然而，粮食价格上涨 40% 导致经济最优氮肥用量增加 9.4 kg N ha ^-1。由于钙质土壤中氮损失高，增加氮肥成本方案是有益的，因为它降低了经济上的最佳比率，从而提高了氮的利用效率，同时也减少了活性氮的损失并保护了环境。