Abstract
This study was conducted to elucidate how changes in critical soil quality characteristics relate to continuous rice cultivation and changes in cropping systems and fertilization in South China over the time span 1980 to 2017. Soil pH, soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP) and potassium (AK) were determined for the samples taken in 2017 and compared to results from the paired samples collected in 1980 by grouping all samples into four cropping systems: continuous paddy fields, new paddy fields developed from uplands, continuous uplands, and new uplands developed from paddy soils. The results show a significant increase in soil pH, AP and AK in all cropping systems, which was, however, coupled with low fertilizer use efficiency. Additionally, a significant increase in SOM came with new paddy soils, whereas a little SOM accumulation and a significantly weakened correlation of TN to SOM occurred in continuous paddy soils. Both low fertilizer use efficiency and deteriorated soil C sequestration function imply a sub-health status of continuous paddy soils. The changes in cropping systems and fertilization, which essentially resulted from expeditious economic growth, should be responsible for the dynamics of C and N and the consequences to soil quality. More experimental studies on balanced fertilization vs. local commonly used fertilization are suggested to probe the mechanisms underlying the C and N dynamics in paddy soils.
Highlights
Rice (Oryza sativa L.) is one of the most essential staple food crops that feeds about 50%of the world’s population but supports and affects the livelihoods and economies of several billion people [1]
Major soil properties were determined for the samples taken in 2017, statistically compared with the results from the paired samples taken in 1980 by grouping all samples into four cropping systems for sample-paired T-test: continuous paddy fields, new paddy fields developed from uplands, continuous uplands, and new uplands developed from paddy soils
Over the time span 1980 to 2017, some improvements in soil quality were observed in all cropping systems in terms of a significant increase in soil pH, soil organic matter (SOM), available phosphorus (AP) and AK, except the continuous paddy fields where an ignorable SOM accumulation was accompanied by an increased soil C:N
Summary
Rice (Oryza sativa L.) is one of the most essential staple food crops that feeds about 50%of the world’s population but supports and affects the livelihoods and economies of several billion people [1]. As of the year 2017, the world’s rice planted area was up to 167.24 Mha and contributed about 26% to the global crop planted area and food production, respectively [2]. Mha of land cultivated with paddy rice and produces about 32% of global rice production [3]. In China, the paddy rice planted area was as high as 31.0 Mha and accounted for 30.2% of the total crop planted area and contributed 34.5% to the total food production in 2017 [2]. The productivity of the rice-rice cropping system is still low and appears to continues to decline because of continuous submergence-induced worse soil environment (e.g., weakened soil structure, increased bulk density and reduced hydraulic conductivity) [4] and subsequent deterioration of soil quality due to the Agriculture 2020, 10, 443; doi:10.3390/agriculture10100443 www.mdpi.com/journal/agriculture.
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