Comprehensive analysis of chemical fertilizer replacement potential by straw returning in field experiments

Straw returning to the field can reduce the use of chemical fertilizers and improve the utilization rate of chemical fertilizers on the basis of improving soil fertility. Straw resources can also be effectively utilized during this time. However, there is a different replacement rate of chemical fertilizer with straw return in China, due to the varying crop planting systems with the various soil fertility. In this study, a critical review was proposed to comprehensively analyze the replacement potential of chemical fertilizer by straw returning in field experiments. The data were collected from the published literature data of "CNKI" from 2000 to 2021 and 32 field experiments of straw returning to fields in Hubei Province from 2013 to 2021. The search keywords were set as "straw return", "nitrogen (N) fertilizer", "phosphorus (P) fertilizer", "potassium (K) fertilizer", and "fertilizer replacement and reduction". The criteria for selecting data from the literature are as follows: 1) The study was conducted in China; 2) The experimental crop was rice, wheat, maize or oilseed rape; 3) The same experiment needed to include the paired treatment and control group. The treatment group was the chemical fertilization reduction with straw return, whereas, the control group was chemical fertilization without straw return. The rest experimental conditions of the treatment and control group were strictly consistent; 4) The level ranges of chemical fertilizer were 150-250 kg/hm2 (N), 40-120 kg/hm2 (P2O5), and 50-150 kg/hm2 (K2O); 5) There were the clear starting and ending years of the experimental period; 6) The published data included the fertilizer amount, crop yield, basic physical and chemical properties of soil. Eventually, 487 published datasets were collected during the years 2000-2021, while, 641 experimental datasets from 32 field experiments that conducted in Hubei Province from 2013 to 2021. After that, the datasets were utilized to determine the proportion of N, P, and K fertilizer reduction by straw return for the major crops, in order to estimate the chemical fertilizer saving potential of straw return on a national scale. Specifically, the average replacement ratios of N, P, and K fertilizers by straw return were 12.2%, 23.9% and 43.5%, respectively. There was no significant difference in the replacement ratios by straw return among the crops. In rotation systems, the average replacement ratio of N and P fertilizer by straw return in the paddy-upland rotation system (e.g., rice monoculture and rice-oilseed rape rotation) were 5.0-12.9 and 18.0-24.8 percentage points higher than those in the upland rotation system (e.g., wheat-corn rotation and corn monoculture). In addition, the supply capacity of soil nutrients was an important influencing factor on the replacement reduction potential of chemical fertilizer (especially P and K fertilizer) by straw return. The reduction ratios of P and K fertilizer by straw return were 9.1-11.5 and 6.2-14.2 percentage points lower in soil with a high nutrient supply capacity than those with the low one, respectively. According to the planting area and fertilizer consumption of various crops in 2020, the national N, P2O5, and K2O fertilizer for the rice, wheat, maize, and oilseed rape seasons could have reduced by 239.48×104, 227.73×104 and 451.98×104 t, respectively, accounting for 12.6%, 25.0%, and 48.5% of the current N, P2O5 and K2O fertilizer consumptions. The total cost of chemical fertilizer was saved 478.98×108 Yuan per year by straw return. A large number of field experiments were implemented for the comprehensive analysis of the reduction potential of chemical fertilizer by straw return. The finding can provide the theoretical basis and data support for the high-use efficiency of chemical fertilizers for the major crops in China.