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The susceptibility of purple soil and intensive tillage render the land prone to erosion under heavy precipitations in a sloping cropland in southwestern China. This study aimed to improve the evaluation of the potential benefits of surface protection tillage and organic matter addition to decreasing nutrient losses. A field plot experiment under natural rainfall conditions was conducted, which employed four management practices: conventional downslope tillage system as control (CK), contour tillage (CT) with organic matter addition (CT + OM), CT with wheat straw mulching (CT + SM), and CT combining straw mulching and organic matter addition (CT + OM + SM). Runoff depth, nutrient loads, and soil erodibility were used to estimate the effects of straw mulching and organic matter addition. Results indicated that the runoff depth under CK was largest during the experimental period, with an average of 16.91 mm, and runoff coefficient average was 32%. Compared with CK, the runoff depth under CT + OM, CT + SM, and CT + OM + SM were reduced by 19%, 34%, and 50%, respectively. A significant difference in soil erodibility indicator among the four treatments was indicated (p < 0.05); CK achieved the highest value, whereas CT + OM + SM obtained the least value. In addition, the contour cultivation (i.e., CT approaches) were more sustainable than the downslope tillage system (i.e., CK). Soil erodibility under CK was 9.83 kg ha −1 mm −1 . Meanwhile, soil erodibility under CT + OM, CT + SM, and CT + OM + SM were 8.49, 6.99, and 6.87 kg ha −1 mm −1 , respectively. These values were 14%, 29%, and 30% lower than that of CK, respectively. CK was more susceptible to accelerated erosion compared with the plots with a surface cover or organic addition. This greater erodibility resulted in higher runoff, sediment yield, and associated nutrient loss for CK. The runoff-associated nitrogen losses were mainly controlled by the runoff rate and soil erodibility (p < 0.05). Variations in NO 3 − –N and NH 4 + –N concentration in runoff water were markedly affected by rainfall events and agricultural practice. A significant logarithmic correlation between NO 3 − –N load and runoff depth was identified. NO 3 − –N was proven to be the main form of inorganic nitrogen loss; therefore, fertilizer application of NO 3 − –N should be reduced in the purple soil region. Soil erodibility significantly influenced the available N losses (p < 0.01), which was best described by a positive logarithmic correlation. Soil nutrient concentration also played an important role in nitrogen loss. However, further research is needed to understand the dynamic interactions between soil erodibility as well as soil and nutrient losses. Results indicated that surface protection by CT + OM + SM is one of the good management practices to reduce soil loss by water erosion in regions with intense agricultural activity. [ABSTRACT FROM AUTHOR]

Sloping farmland (SpF) is an important component of cultivated land resources. In the context of food security and sustainable agricultural development, comprehensive SpF utilization has drawn wide and increasing attentions. A systematic analysis on the research progress of comprehensive SpF utilization is critical for a better understanding of the sustainable agricultural cultivation, facilitating the macroeconomic decision-making. This paper conducted a quantitative analysis of literature related to comprehensive SpF utilization over the past few decades (1946–2019) by using scientometrics methods, with the objectives to: (1) identify the research hotspots and summarize the relevant research processes in different time periods; (2) reveal the temporal evolution of those hotspots. Our results showed: 1) research on SpF dramatically increased over the past few decades (1946–2019), which can be classified into four chronological periods (I, II, III, and IV); (2) research regarding land productivity improvement and hydrological and erosion processes on SpF were dominant in the period I; (3) the research hotspots were switched to land use changes and associated soil erosion response, ecological disturbance and restoration as the social demand was intensifying in the period II; (4) the research focus of period III was aiming at the governance and rational utilization of SpF and gradually transforming to a large regional scale; (5) the intercross and penetration between disciplines had been continuously enhanced in the period IV, and the application of high and new technologies had also promoted the diversification of research methods, with aims to achieve sustainable agricultural development. Although considerable progress had been achieved around the world, more theoretical and empirical studies are required to understand the comprehensive SpF utilization and their implications to better support sustainable agricultural development. • Comprehensive sloping farmland utilization was systematically reviewed. • Research focus has changed from land productivity to multi-disciplinary fields. • Methodology is developing to be on multiple scales involved in information technology. [ABSTRACT FROM AUTHOR]

Accurate estimation of reference evapotranspiration (ET 0 ) is of importance for regional water resource management. The present study proposed two artificial intelligence models, random forests (RF) and generalized regression neural networks (GRNN), for daily ET 0 estimation. Meteorological data including maximum/minimum air temperature, solar radiation, relative humidity, and wind speed during 2009 ∼ 2014 from two stations in southwest China were used to train and test the RF and GRNN models by using two input combinations, including complete data and only temperature and extraterrestrial radiation (R a ) data. The k-fold test was adopted to test the performance of models according to temporal and spatial criteria and data set scanning procedures. The results indicated that both local and external RF and GRNN models performed well for estimating daily ET 0 , and RF was slightly better than GRNN generally. The high fluctuations in the accuracy ranges justify the importance of applying k-fold test for assessing the model performance, which could avoid drawing partially valid conclusions from model assessments based on simple data set assignment. Overall, both temperature-based RF and GRNN models can accurately estimate daily ET 0 , which is helpful for irrigation scheduling in southwest China. [ABSTRACT FROM AUTHOR]