How to reasonably determine nitrogen fertilizer application rates in precision quantitative rice cultivation

The quantification of nitrogen needs to consider the fertilizer requirements of high-yield rice, the pattern of soil nitrogen supply, fertilizer characteristics and the current-season utilization rate, as well as various changes during the growth period, and includes two parts: total nitrogen quantification and nitrogen fertilizer application methods.

Determination of total nitrogen amount: the nitrogen, phosphorus and potassium ratio obtained through soil testing and fertilizer recommendation trials should be regarded as the reasonable ratio for the locality; then, based on the nitrogen fertilizer application rate that achieves high yield locally, and according to the reasonable nitrogen, phosphorus and potassium ratio from the local soil testing and fertilizer recommendation “3414” trial, the specific application rates of nitrogen, phosphorus and potassium for high-yield cultivation are determined. The total nitrogen application rate is determined by the Stanford difference method: total nitrogen application rate (kg/mu) = [nitrogen requirement for target yield (kg) - soil nitrogen supply (kg)] ÷ current-season utilization rate of nitrogen fertilizer (%). The greater the total nitrogen amount, the lower the fertilizer utilization rate; with different application scheduling ratios, the fertilizer utilization efficiency also differs. Generally speaking, under the premise of maintaining the local yield level unchanged or slightly increased, adopting precision quantitative rice cultivation technology can save 20%-30% of fertilizer.

Nitrogen fertilizer application methods: trial demonstrations have shown that heavy application of panicle fertilizer can promote panicle differentiation and increase the number of grains per panicle. The optimal ratio of basal and tillering fertilizer to panicle fertilizer is 5:5 or 6:4. This fertilization method can achieve high yield and significantly improve fertilizer use efficiency.

Nitrogen fertilizer application timing: the timing of nitrogen application mainly follows two principles. First, ensure that rice does not lack nitrogen during the effective tillering stage, and maintain a reasonable dynamic of gradually declining nitrogen concentration, so that it drops to the nitrogen-deficient level by the ineffective tillering stage. Second, from the beginning of panicle differentiation, the nitrogen level gradually increases, and after entering secondary rachis branch differentiation it reaches a non-nitrogen-deficient level and is maintained until the milk-ripe stage; after milk ripeness it declines reasonably, which is beneficial for improving matter translocation. Basal fertilizer is applied before transplanting, tillering fertilizer is applied 5-7 days after transplanting, flower-promoting fertilizer is applied at the beginning of young panicle differentiation, and flower-preserving fertilizer is applied when the second-to-last leaf grows.