Trends of basic soil productivity in paddy soil under long-term fertilization in China

【Objectives】 The paddy rice system shows a great stability to climate and soil basic fertility which makes a great contribution to rice yield, so soil basic fertility represents a key contributor for high and stable rice yield. Therefore, investigating changing trends of paddy soil basic fertility in different regions under long-term fertilization can provide scientific basis not only for sustainable rice production but also for assessing and proposing proper fertilization strategy. 【Methods】 An experiment was designed to include two treatments, CK (no fertilizer) and NPK (conventional fertilization). The rice yield under the CK represents soil basic fertility, and the proportion of the crop yield under the CK to that under the NPK represents soil basic fertility contribution. Seven long-term field experiments in paddy crop systems (rice-rice, and rice-wheat rotation) were selected to investigate dynamic trends in soil basic fertility and its contribution, and to examine relationships between soil basic fertility contribution and rice yield or other indicators. 【Results】 In general, the rice yields under CK remain constant with a mean change rate of-0.3 kg/(hm2a) only. Soil basic fertility trends show differences among paddy soil types, and soil basic fertility levels show a declining trend for reddish paddy soils and remain constant for purple paddy soils. Under CK, both the late-rice and single-rice yields show increasing trends with rates of 1.6 and 29.2 kg/ (hm2a), respectively, while the early-rice yields shows a declining trend with a rate of 20.0 kg/ (hm2a). The declining rates of rice yields in the CK treatment are highest at Baisha (BS) and Wangcheng (WangC) sites, up to 47-82 kg/ (hm2a). Those of early-rice at Nanchang (NC) site and single-rice at the Wuchang (WuC) and Suining (SN) sites show increasing trends with the rates of 44-81 kg/ (hm2a). On average, the rice soil basic fertility contribution ranges from 42% to 68%, with a mean value of 59.7%. The contribution percentages are 55.1%, 67.1% and 54.9% for early-rice, late-rice and single-rice, respectively. Soil basic fertility is significantly positively correlated with sustainable yield index (SYI) in the CK treatment (r=0.655, n=13). The mean annual rice yield is 5100 kg/hm2 under the NPK treatment, which is significantly higher than that under the CK treatment (2911 kg/hm2) in the seven sites. The contribution of the NPK fertilization to rice yield is 40.3%.【Conclusions】 Under no fertilizer, the yields show stable or increasing trends for late-rice and single-rice, but show a declining trend for early-rice especially in red paddy soils. The rice yields are most stable for the purple paddy soils. Under the fertilization, the rice yields are stable across all the sites. From a long-term view, increasing soil basic fertility can be effective in elevating rice yield sustainability.