JIA-2019-11

2620 WANG Shi-chao et al. Journal of Integrative Agriculture 2019, 18(11): 2619–2627 production in China (Chen et al. 2011; Yan et al. 2018). However, certain practices and characteristics in long-term cropping systems such as straw burning or removal, fertilizer imbalance, and unsustainable land use have resulted in rapid declines of soil fertility and crop productivity (Yu et al. 2006; Guarda et al . 2004; Shapiro and Worthmann 2006). Therefore, in order to meet the growing demand for food, we need to understand the past trends of inherent soil fertility in different cropping systems to explore soil productivity potential in the future. Increasing inherent soil fertility depends on the optimal fertilization, tillage, and straw return (Barbieri et al . 2008; Aynehband et al . 2010; Liu and Wiatrak 2012; Dikwatlhe et al . 2014; Mbuthia et al . 2014). One study reported that inherent soil fertility is a key contributor to achieving high and stable crop yields (Fan et al. 2013). In addition, soil fertility varies among regions, cultivation years, and cropping systems. In previous studies, the soil contribution to productivity has been used to quantify the multifactorial effects including climate condition, soil fertility, fertilization, and crop type by crop yield from long-term no fertilizer treatment (Fan et al. 2013). The contribution percentage of inherent soil productivity (CPISP) of a cultivated soil reflects that soil’s ability to support crop yield without fertilizer inputs. For example, a soil with a low CPISP value will require much more fertilizer input to achieve maximum yields than a soil with a high CPISP value (Kagabo et al. 2013; Liu et al. 2013; Niu et al. 2013; Sattari 2014; Yang et al. 2014; Qin et al. 2015). Thus, knowledge of soil CPISP values will facilitate identifying soils with the potential to increase overall productivity while minimizing inputs, which will lead to less environmental degradation and improved farmer profitability. However, CPISP was characterized by grain yields from on-farm trials for one year or long-term no-fertilization in previous research (Fan et al. 2013; Zha et al. 2014). In fact, soil nutrients tended to decrease continuously under long-term no-fertilization, so the yield could not reflect the changes in CPISP. In addition, in the first year of these experiments, the changes in soil nutrient status and the soil microenvironment were unstable. In order to accurately assess the changes of CPISP, we defined CPISP3 as the average ratio of CPISP for the first three years after each monitoring point. Many fertilizer efficiency experiments have been conducted in China (Ma et al. 2012; Zha et al. 2014), but data from these experiments have not been used to systematically assess CPISP at a national level. This study uses data from a national programme that focused on soil fertility in various regions of China starting in 1984. As crop varieties and planting techniques from the early 1980s have been improved, inherent soil fertility has changed greatly (Fan et al. 2012; Zhang et al. 2013). In addition, the CPISP showed a large difference in the cropping systems (Fan et al. 2013). Thus, the data from long-term experiments (LTEs) were used to detect changes in CPISP over time in China’s typical cropping systems. It was hypothesized that CPISP estimated by changing crop yield will differ among different cultivation years and cropping systems. Based on the above, the major objectives of this study were to: (1) determine the current CPISP values in China; (2) analyse the trend of CPISP values over the past three decades; (3) evaluate how CPISP values vary for typical cropping systems in China; and (4) discuss whether the CPISP concept has value in predicting future fertilizer requirements of different crop varieties. 2. Materials and methods 2.1. Experimental sites Based on cropping systems and their distribution areas, soil type, production capacities, management levels, and technology inputs in the main national agricultural districts of China, the Ministry of Agriculture established national monitoring points to assess cultivated land quality (Appendix A). In the first phase, which lasted from 1984 to 1990 (the 1980s), 196 monitoring sites were developed. These sites were adjusted or added to in the second phase, which lasted from 1996 to 2000 (the 1990s), and again in the third phase, which lasted from 2004 to 2013 (the 2000s). In 2013, there were a total of 362 monitoring sites, of which some were begun in the 1980s, some in the 1990s, and some in the 2000s. The monitoring sites were located in 30 provinces in China and covered 35 soil groups of cultivated land, such as paddy soil, fluvo-aquic soil, black soil, brown soil, and red soil. Approximately 84.5% of the monitoring sites were planted with three grain crops: rice ( Oryza sativa L.) (29.6%), wheat ( Triticum aestivum L.) (29.8%), and maize ( Zea mays L.) (25.1%) (Ren et al. 2009). These data were used to calculate CPISP3 and for current CPISP analysis. In this study, CPISP3 was estimated by assessing crop yields without added fertilizer. The no fertilizer treatment received neither chemical fertilizer nor manure in the first three years of the field experiment but received other agricultural management measures such as insect control and irrigation. These fields received conventional agricultural practices before the site experiment including fertilizer application and irrigation. The changes in CPISP over time and its variations were studied for two cropping systems practised in different regions: 1) mono-cropping system of maize or wheat in Northwest China and continuous maize or wheat/soybean/ maize in Northeast China; and 2) double-cropping systems of wheat-maize rotation in northern China or wheat-rice and