Temporal and spatial distribution characteristics of crop straw nutrient resources and returning to farmland in China

Abstract: Crop straw resource in China is plentiful, but in different regions the straw resource capacity, the corresponding nutrient resource capacity and available amount of returning to farmland as well as the changes over time have not been very clear. Based on official statistical data and literature review, this study analyzed the capacity of crop straw, the corresponding nutrient nitrogen (N), phosphorus (P) and potassium (K) and available amount of returning to farmland in different time slots at provincial level, aiming to provide scientific basis and reference for rational utilization of straw nutrient resources and nutrient management under zero growth of chemical fertilizer. Results indicated that the capacity of crop straw and its NPK nutrients increased by 85.77% and 104% from 1980s to 2010s, respectively. Among the regions, the increase of crop straw capacity and NPK nutrients in Northwest, Tibet Autonomous Region and Heilongjiang Province was more obvious. The crop straw and its nutrient capacity in North Plain, middle and lower reaches of Yangtze River, Sichuan Basin and Heilongjiang Province accounted for two-thirds of the total capacity in China. By the 2010s, the total crop straw and its total N, P and K capacity in China have reached 9.01×108 and 2 485.63×104 t, respectively, equivalent to per unit area of farmland of 6 665.56 and 183.91 kg/hm2, 1 601.18 and 56.85 kg/hm2 more than those in 1980s, respectively. Great variability existed among different regions in the capacity of straw and its nutrients from specific kinds of crops. In 2010s, the proportions of crop straw and its nutrient capacity from cereal crops accounted for 69.86% and 56.47% of the total capacity in China, respectively, and the highest proportions of cereal crop straw and its nutrient capacity occurred in Northeast region. The capacity of crop straw and nutrient from fruits and vegetables accounted for 9.67% and 21.99% of the total capacity in China, respectively, and the Northeast region had the highest proportions of straw and nutrient capacity of fruit and vegetable. The proportions of straw and nutrients capacity from beans, potatoes, oil crops, cotton and other fiber crops were relatively small. The amount of direct straw returning to farmland has continually increased from 1980s to 2010s, while the amount of straw returning to farmland after burning increased from the 1980s to 2000s, and decreased in 2010s. However, the total amount of straw NPK nutrients returning to farmland has increased continually from 1980s to 2010s. The total NPK nutrients increased from 583.92×104 t (N 97.81×104 t, P2O5 40.10×104 t and K2O 446.01×104 t) in 1980s to 1 770.66×104 t (N 574.53×104 t, P2O5 105.53×104 t and K2O 1 090.60×104 t) in 2010s, equivalent to per unit area of farmland of 60.89 kg/hm2 (N 10.20 kg/hm2, P2O5 4.18 kg/hm2, K2O 46.51 kg/hm2) in 1980s to 131.0 kg/hm2 (N 42.5 kg/hm2, P2O5 7.8 kg/hm2, K2O 80.7 kg/hm2) in 2010s. The ratio of crop straw NPK nutrients returning to farmland was 47.92%, 56.16%, 60.11% and 71.24%, respectively in 1980s, 1990s, 2000s and 2010s. From 1980s to 2000s, the increase of the ratio of crop straw NPK nutrients returning to farmland in Inner Mongolia, Xinjiang and Heilongjiang was obvious, but the total amount of crop straw NPK returning to farmland in the North Plain, the middle and lower reaches of the Yangtze River and Sichuan Basin accounted for more than two-thirds of total crop straw NPK returning to farmland in China.