Analysis and evaluation of farmland soil nutrient balance in Heilongjiang Land Reclamation Areas, China

Efficient nutrient utilization has become an essential part of green development in modern agriculture. Evaluation on the nutrient balance of farmland soil is therefore critical to the Heilongjiang Land Reclamation Area (HLRA), one of the major grain-producing regions in China. HLRA has produced 410 million tons of grain since 1949, currently serving as a typical representative of agricultural mechanization and modern production. In HLRA, the total grain output was 2 279.64× 104 t in 2018, accounting for 3.47% of the national total. Taking the HLRA as the research subject, this study aims to develop a nutrient balance method for the evaluation on the input and output of N, P, and K from farmland soil during the period from 2000 to 2018. The results showed that: 1) From 2000 to 2018, the N, P, and K inputs of farmland soil in HLRA showed a steady-increase-decline trend. In 2018, the N, P and K input decreased to 6.55×108, 1.27×108 and 5.29×108 kg. The N input mainly came from chemical fertilizer, organic fertilizer, and biological nitrogen fixation, whereas, the P and K inputs were mostly from chemical fertilizer and straw returning to field. 2) The N, P, and K outputs of farmland soil in HLRA also showed a steady-increase-decline trend from 2000 to 2018. In 2018, the N, P and K outputs decreased to 6.12×108, 7.34×107 and 4.88×108 kg. The main ways of N and P outputs were for grain and straw, with special emphasis on the N output from ammonia volatilization, whereas the way of K output was mainly for straw. 3) The N, P, and K inputs per area of farmland soil in HLRA also showed a steady-increase-steady trend from 2000 to 2018. The N, P and K inputs per area in 2018 were 228.08, 44.32 and 183.98 kg/hm2. The N, P, and K inputs per value of farmland soil in HLRA showed a decline trend from 2000 to 2018. Specifically, the N, P, and K inputs per value in 2000 were 94.86, 18.43, 76.52 kg/104 yuan. There was an increase in the N and P utilization efficiency of farmland soil in HLRA, but a decrease in that of K, indicating 51.03% for N, 27.98% for P, and 10.04% for K in 2018. There was an increase trend in the N profit and loss of farmland soil in HLRA, and a steady trend for that of P, while a decline trend for that of K. The N profit and at an excellent level, compared with that from Australia, Canada, France, Germany, Japan, UK, and the USA. But a relatively low level occurred for the profit and loss. It infers that the N and K were in a nutrient balance state since 2017, whereas P was in a nutrient surplus condition. The reason can be that the P input into the farmland was easily fixed by soil. At the current stage, the fertilizer input in HLRA was mainly relying on chemical fertilizer, whereas, the amount of organic fertilizer was relatively low. This arrangement can be not conducive to fertilizing soil and slowing down the degradation of black soil. Therefore, a sound recommendation for HLRA can be made to develop various methods, such as subsidies and demonstration, further to gradually promote the application of organic fertilizers. Besides, a long-term monitoring of nutrient balance in the farmland soil was required in the near future, in order to scientifically adjust and optimize management strategies of soil nutrients, and thereby to improve nutrient utilization efficiency and food security in green development of modern agriculture.