JIA-2019-11

2622 WANG Shi-chao et al. Journal of Integrative Agriculture 2019, 18(11): 2619–2627 crop type, climate and fertilization (Fig. 1). CPISP3 data from 1086 on-farm trials between the 1980s and 2000s were examined under no-fertilization treatment. The average CPISP3 for the three studied crops was 53.8% (±20.4, SD) ( n =1086), with crop averages of 58.4, 50.0 and 50.7% for rice, wheat and maize, respectively. Significant differences in CPISP3 were found between rice and wheat (or maize) ( P <0.05) but not between wheat and maize. The CPISP3 values in the 1990s was much higher than those in the 1980s and 2000s. Fig. 2 shows that the CPISP3 for each crop changed over time, though these changes were not significant for all crops. The CPISP3 for rice exhibited no significant change with time. In contrast, the CPISP3 for wheat increased by 20.8% from the 1980s to the 1990s (from 46.2 to 55.8%) and then decreased significantly from the 1990s to 2000s (from 55.8 to 44.6%). Finally, the CPISP3 for maize was significantly higher in the 1990s than during the 1980s and 2000s. 3.2. Trends of CPISP in typical cropping systems Mono-cropping system Most upland mono-cropping areas are in Northwest and Northeast China. The CPISP data for LTEs in typical cropping systems established in China reflected changes in the inherent soil productivity under no-fertilization treatment. The CPISP results for wheat and maize from 1979 to 2013 in Northwest China are shown in Fig. 3-A. In the irrigated area, CPISP declined significantly over time. Regression analysis revealed that CPISP declined at approximately 0.4% per year in the rainfed area (Fig. 3-A). In contrast, the CPISP of the irrigated area decreased from 89.7% in 1982 to 25.7% in 2007. The CPISP decreased by 4.5% annually within the first 10 years and then stabilized over the next 10 years in the irrigated area (Fig. 3-A). In addition, CPISP followed an exponentially decreasing trend over time under continuous maize cropping in Northeast China (Fig. 3-B). The regression revealed that the CPISP value decreased from 80.8 to 40.9% during the first 10 years, with an average loss of 4.0% per year. Over the next 10-year period, the CPISP stabilized in the range of 36.6–45.4%. After three years of maize/soybean/wheat mono-cropping, the CPISP decreased from 83.0 to 76.8% at an initial rate of decrease of 2.1% annually. Subsequently, this rate of decrease slowed, and CPISP stabilized in the range of 63.6–76.8%. Double-cropping systems Fig. 4-A shows the trends of CPISP in double-cropping systems of wheat-maize rotation in northern China and wheat-rice and rice-rice rotation in southern China. For the wheat-maize rotation, the average CPISP of wheat declined continuously during 1979–2012. Pearson correlation analysis indicated that the CPISP was negatively correlated with the experimental years ( R 2 =0.53, P <0.01) and the rate of CPISP decline was 1.1% per year. The CPISP value fell in the range of 22.6–73.5% in the upland-paddy rotations of wheat and rice in southern China CPISP3 (%) 0 20 40 60 80 100 120 (469) (340) (277) a b b (181) (409) (496) b a b (1 086) Crop Year Overall Rice Wheat Maize 1980s 1990s 2000s CPISP3 (%) 0 20 40 60 80 100 1980s 1990s 2000s 1980s 1990s 2000s 1980s 1990s 2000s (83) a (139) a (247) a (52) ab (145) a (143) b (46) b (106) a (125) b Rice Wheat Maize Fig. 1 The total varying trend of contribution percentage of soil productivity during the first three years. CPISP3, the average ratio of inherent soil productivity at the first 3 years after each monitoring point. Different letters indicate significant difference at P≤ 0.05. Solid and dashed lines indicate mean and median CPISP3, respectively. The lower and upper boundaries, bars and dots in or outside the boxes indicate 25th and 75th, 5th and 95th, respectively. Numbers of observations are shown in parenthesis. Fig. 2 Box plot of the average ratio of inherent soil productivity at the first 3 years after each monitoring point (CPISP3) for different crops and periods. Different letters indicate significant difference at P≤ 0.05. Solid and dashed lines indicate mean and median CPISP3, respectively. The lower and upper boundaries, bars and dots in or outside the boxes indicate 25th and 75th, 5th and 95th, respectively. Numbers of observations are shown in parenthesis.