Abstract:

【Objective】The rice planting area in Liaoning Province is approximately 500 000 hm², decreasing by one fifth from the size it was 10 years ago. However, due to the continuous increase in unit production, the annual output has been stable at over 4 million tons. As the main producing area with the highest unit yield for japonica rice in Liaoning Province, the potential and space remains to be further studied in the context of zero growth of chemical fertilizer, at the same time, both soil fertility and rice yield should be taken into consideration for chemical fertilizer application reduction. 【Method】Three major rice producing areas were investigated in 2020, including the Liaohe Delta, the Southeastern Area along the Yellow Sea, and the North-central Area of Liaoning. In each rice planting area, the representative towns with high, medium and low yields were selected as research spots. In each research spot, two to five villages (ten households per village) were selected to carry out the investigation, counting up to 590 questionnaires. The recommended amount of nitrogen (N) fertilizer for each rice growing area was determined on the basis of previous studies. According to crop nutrient requirement and soil nutrient status in paddy fields, the suitable amount of phosphate (P) and potassium (K) fertilizer was estimated by the measurement and monitoring method of P and K. Based on this analysis, the potential of chemical fertilizer reduction for paddy rice in Liaoning Province was calculated. 【Result】Average yields in the Liao River Delta, the southeastern area along the Yellow Sea and the north-central area of Liaoning were 10.4, 7.7 and 8.7 t·hm^-2, respectively. The difference within the same rice planting area was about 4 t·hm^-2, while the difference between different rice planting areas was about 2.7 t·hm^-2. The average amount of N, P₂O₅ and K₂O for the different paddy rice fields in Liaoning Province were 229.4, 102.8 and 91.1 kg·hm^-2, respectively. Compared with the amount of fertilizer application before 2004-2017 year, the N fertilizer was reduced by 12%-32% and the P and K fertilizer was increased to some extent. The ratio of N, P and K fertilizer was 2.2﹕1﹕1. The average amounts of N and P fertilizer application varied greatly. The difference of the average amount between the maximum and the minimum is 79.5 kg·hm^-2for nitrogen and 35.4 kg·hm^-2for P₂O₅. The difference between the amounts of pure N application by farmers was about 4-fold. About 2.5% of the farmers did not apply K fertilizer, and some farmers did not apply P fertilizer. The maximum application of P₂O₅ and K₂O were 294.5 and 225.0 kg·hm^-2, respectively. The phenomenon of unscientific fertilization still existed in these regions. Taking the average yield increase of 5% in the last three years as the target yield, the recommended fertilizer amount was calculated. The target yield in the rice planting area of the Liaohe Delta was 10 000 kg·hm^-2. The recommended application of N, P₂O₅ and K₂O were 234, 111 and 101 kg·hm^-2, respectively. About 82.1% of the farmers had low N fertilizer efficiency. This excessive N fertilizer application was a serious problem. About 21.7% of the farmers could potentially reduce N fertilization by 13.7%, about 9.6% of farmers could potentially reduce P fertilizer by 5.1%, and K fertilizer needed to be supplemented appropriately. Target yield in the Southeastern Area along the Yellow Sea was 7 500 kg·hm^-2. The recommended application of N, P₂O₅ and K₂O were 179, 83 and 76 kg·hm^-2, respectively. About 68.0% of the farmers had low P fertilizer efficiency with a generally excessive P fertilizer application phenomenon. 28.0% of the farmers could potentially reduce the amount of P fertilizer by 18.6%. About 20% of farmers fell in the low-yield and low-efficiency levels of N and K fertilizer. The application reduction potential was around 7%. The target yield in the North-central Area of Liaoning was 9 000 kg·hm^-2. The recommended application of N, P₂O₅ and K₂O were 210, 80 and 91 kg·hm^-2, respectively. About 30% of farmers had the potential to reduce the application of N, P and K fertilizers. The application reduction potential for N, P and K fertilizer was approximately 1%, 1% and 4%, respectively. 【Conclusion】After the implementation of a five year ‘zero growth in fertilizer use’ policy, the situation of fertilizer application in the paddy fields of Liaoning Province has be drastically improved, but the phenomenon of unscientific fertilization by farmers still exists. In the Liaohe Delta, the excessive application of N fertilizer was prominent. About 21.7% of the farmers could reduce the application of N fertilizer by 13.7%. In the Southeastern Area along the Yellow Sea, the phenomenon of excessive application of P fertilizer is common. About 28.0% of the farmers could reduce P fertilizer input by 18.6%. In the north-central area of Liaoning Province, about 30% of farmers in rice planting areas have the potential to reduce the application of chemical fertilizers. The percentage for potential application reduction of N and P fertilizer was about 1%, while that of K fertilizer was about 4%.

Key words: rice, application reduction of chemical fertilizer, threshold of chemical fertilizer, partial factor productivity, Liaoning Province