Abstract:

【Objective】Heilongjiang has a paddy field of more than 3.2 million hectares, it is the largest province in China with rice fields. In the past ten years, rice production in Heilongjiang Province has been hovering at 7 000 kg·hm ^-2, while it was the province with the lowest amount of fertilizer in paddy fields in China. Under the background of “fertilizer zero increase”, whether is there potential for fertilizer saving in Heilongjiang Province remains to be studied. 【Method】We investigated paddy field fertilization across different farms in the main rice producing areas in Heilongjiang Province. In 2005, the survey areas were Wuchang, Fangzheng, Mulan, Ning'an, Qing'an, Tieli, Shangzhi and Acheng; in 2008, the survey areas were Mishan, Hulin, Qing'an, Wuchang, Ning'an, Fangzheng, Luobei, Huachuan, Fujin and Shangzhi; the survey areas in 2015 were Wuchang, Fangzheng, Ning'an, Hulin and Qing'an. From each county, a random township was selected, and 2 or 3 villages were randomly selected from each township, then 10 households were surveyed in each village. From 2009 to 2010, more than 80,000 soil samples from the main rice producing areas in Heilongjiang Province were collected, and the phosphorus and potassium nutrient contents in 0-20 cm soil layer were determined. The nitrogen application rate was estimated through theoretical appreciate application rate method. Based on the crop nutrient demand and the soil nutrient status of the paddy field, phosphorus and potassium application rate was evaluated. Fertilizer reduction potential was analyzed in Heilongjiang Province.【Result】According to the research data, the average rice yields in 2005, 2008 and 2015 were 6 427, 7 593 and 7 142 kg·hm ^-2, respectively, and the average annual output was 7 104 kg·hm ^-2. The crop yield differed between farms with a range of nearly 5 000 kg·hm ^-2. The average amount of N, P₂O₅ and K₂O in paddy fields were 141.0, 56.6 and 51.6 kg·hm ^-2, respectively, and the difference in the amount of NPK fertilizers was more than 300 kg·hm ^-2. Therefore, the results showed that fertilization variation among farmers was large, so the problem of blind fertilization was prominent. The content of available phosphorus and available potassium in the paddy soil of Heilongjiang Province were about 26 mg·kg ^-1 and 138 mg·kg ^-1, respectively. The variation of available phosphorus in soil exceeded 40%, and soil fertility varied greatly among different regions. High level phosphorus and potassium accounted for above 70% samples. To reach rice production levels of 7 500 kg·hm ^-2, the theoretical suitable nitrogen application rate was 105 kg·hm ^-2. Only 20% of farmers achieved high yield and high nitrogen efficiency, and 70% of the farmers had fertilizer-saving potential with nitrogen reduction of 26%. Through fertilizer saving, the grain produced per kilogram of nitrogen could be increased from 50 kg to 70 kg. According to the current yield and soil nutrient status, the appropriate amount of phosphate and potassium fertilizer in paddy fields was only 41.6 and 35.9 kg·hm ^-2, which could be reduced by about 30%. Among the surveyed households, farmers whose fields had the potential for phosphorus and potassium-saving accounted for 71% and 72% of the total, respectively, among which the low-yield and low-efficiency farmers accounted for 30% of the total farmers, where the fertilizer-saving potential was the largest.【Conclusion】Although Heilongjiang was the province with the lowest fertilization rate in China, about 70% of farmers were high-yield but low efficiency, or low-yield and low efficiency, so the problem of excessive fertilization was prominent, and the fertilizer-saving potential was more than 20% in Heilongjiang Province.

Key words: cold area, paddy field, fertilizer application rate, fertilizer reduction potential, yield, Heilongjiang Province