Spatial-Temporal Variation Characteristics of Wheat and Maize Stalk Resources and Chemical Fertilizer Reduction Potential of Returning to Farmland in Recent 30 Years in China

China has rich wheat and maize stalk resources. It is necessary to clarify the spatial-temporal characteristics of the wheat and maize stalk resources, the corresponding nutrient resources and chemical fertilizer reduction potential through stalk incorporation, which can provide decision basis for promoting the utilization of stalk resources and reducing chemical fertilizer application.

Based on the soil long-term monitoring data of the Ministry of Agriculture and Rural Affairs in wheat and maize planting areas of China from 1988 to 2019, this study analyzed the amount of wheat and maize stalk and its nutrient resources and fertilizer reduction potential through stalk incorporation in different years in each region of China.

The annual average amount of wheat and maize stalk resources reached 1.62×10⁸ t and 4.23×10⁸ t, respectively in 2010s, which were increased by 0.16×10⁸ t and 2.04×10⁸ t compared with 1990s, respectively. The annual average amount of wheat and maize stalk NPK resources reached 278.19×10⁴ t and 901.08×10⁴ t, respectively, which were increased by 27.97×10⁴ t and 434.82×10⁴ t compared with 1990s, respectively. Both of them increased most in North China (NC). The annual average amount of wheat stalk resources and NPK resources decreased first and then increased with planting years, while maize increased. In the first stage (1990s to 2000s) and the second stage (2000s to 2010s), the annual variation rate (AVR) of wheat stalk resources were -42.47×10⁴ t·a^-1 and 205.10×10⁴ t·a^-1, and the AVR of nutrient resources were -0.26×10⁴ t·a^-1 of N, -0.03×10⁴ t·a^-1 of P, -0.44×10⁴ t·a^-1 of K and 1.27×10⁴ t·a^-1 of N, 0.14×10⁴ t·a^-1 of P, and 2.11×10⁴ t·a^-1 of K, respectively. In the first stage and the second stage, the AVR of maize stalk resources were 397.82×10⁴ t·a^-1 and 1 643.60×10⁴ t·a^-1, and the AVR of nutrient resources were 3.46×10⁴ t·a^-1 of N, 0.56×10⁴ t·a^-1 of P, 4.46×10⁴ t·a^-1 of K and 14.30×10⁴ t·a^-1 of N, 2.30×10⁴ t·a^-1 of P, and 18.41×10⁴ t·a^-1 of K, respectively. There were more than 80% of wheat stalk and its nutrient resources distributed in NC and Middle and lower reaches of Yangtze River (MLRYR), with the highest in NC (0.93×10⁸ t, 160.31×10⁴ t of NPK), and the lowest in Southwest China (SW) (0.09×10⁸ t, 16.05×10⁴ t of NPK). About 70% of maize stalk and its nutrient resources were distributed in Northeast China (NE) and NC, with the highest in NE (1.39×10⁸ t, 296.96×10⁴ t of NPK), and the lowest in MLRYR (0.21×10⁸ t, 44.40×10⁴ t of NPK). The annual average nutrient-release amount of wheat stalk incorporation per unit area were 21.1 kg·hm^-2 of N, 3.0 kg·hm^-2 of P and 62.3 kg·hm^-2 of K in China, with the highest in NC, and the lowest in SW. The annual average nutrient-release amount of maize stalk incorporation per unit area were 48.6 kg·hm^-2 of N, 10.6 kg·hm^-2 of P and 97.7 kg·hm^-2 of K in China, with the highest in Northwest China (NW), and the lowest in SW. The annual average nutrient-release amount of wheat and maize stalk incorporation per unit area increased continually during 1988-2019. The proportion of wheat stalk returning nutrients to the annual chemical fertilizer application were 9.13%-10.82%, 4.26%-6.43% and 88.02%-111.86%, respectively, and that of maize stalk were 22.99%-24.37%, 16.04%-28.67% and 150.29%-171.95%, respectively.

In general, using wheat and maize stalk properly could satisfy the basic potassium requirement for crop production and reduce the application of about 10%-20% nitrogen fertilizer and 5%-20% phosphorus fertilizer. Making full use of stalk resources was an important guarantee for reducing fertilizer application and increasing efficiency.