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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]

Understanding the long-term impact of C-N management practices on soil moisture content (SMC) is crucial for sustainable agriculture, particularly in mitigating seasonal droughts and storm rainfall constraints. A multi-year (2014–2018) field experiment was conducted, with high-frequency measurements and consideration of a full life cycle, as well as multiple vertical layers (0–100 cm, with intervals of 20 cm). Treatments were arranged in a split plot design with nitrogen (N) fertilizer input (N 80% and N 60%) as the whole-plot factor, and Carbon (C) treatments (C org =organic fertilizer, C straw =straw mulching and full returning, C integ = C org + C straw) were considered as the split-plot factor. The results demonstrated the C integ treatment resulted in the highest increase in the five-year averaged SMC (approximately 6.60% greater than C org), followed by the C straw treatment. Additionally, the N60% treatment resulted in significantly higher SMC compared to the N80% treatment, with a range of 1.71–4.12% increase across the life cycle. Furthermore, the research revealed that the average SMC increased the most during the jointing-heading period and the least during the heading-maturity period across all treatments. The vertical results indicated a higher efficiency in water retention within the shallow layers (0–20 cm, 20–40 cm) compared to the deeper layers (80–100 cm) for all treatments. The study recommends adopting integrated C-N management practices, considering life cycle periods and vertical layers, to optimize soil moisture content. It offers valuable insights for optimizing soil moisture management strategies, alleviating seasonal droughts, enhancing water-use efficiency, and fostering sustainable agricultural practices. • Organic fertilizer integrated into straw returns increased average SMC by 5.5∼6.6% compared with separate applications. • N fertilizer at 144 kg/ha increased average SMC more (1.71%∼4.12%) than 192 kg/ha. • Average SMC increased most in the jointing-heading period and least in the heading-maturity period. • Shallow soil layers show a higher holding-water efficiency than deep soil layers. [ABSTRACT FROM AUTHOR]

The expansion and intensification of human activities have resulted in excessive nitrogen (N) in rivers, causing worldwide concern. To effectively manage agricultural non-point source pollution and ensure a safe drinking water supply in watersheds, it is crucial to trace and quantify the primary sources and spatial distribution patterns of N. In response to the challenge of unclear sources and agricultural non-point source pollution, this study utilised the Bayesian isotope mixing model and Soil and Water Assessment Toolmodel to identify the dominant nitrate sources and transformation processes. These models were employed to quantify N retention by the mainstream and tributaries in the Bai River Basin, which directly impacts the safety of drinking water in Beijing. Total N (TN) concentrations in the Yunzhou Reservoir (4.22 ± 0.04 mg.L˗1) and Miyun Reservoir (2.88 ± 0.62 mg.L˗1) inlets in autumn and winter were V class (2 mg.L˗1) category as per GB 3838–2002 standards. This implies higher risks of eutrophication and algal blooms exceeding the standards at individual points and seasons in the Bai River. Fertilisers were the main nitrate source in the Bai River Basin, contributing 44.6% during the dry season and 62.9% during the wet season, suggesting that nitrate is more susceptible to leaching and runoff during rainy periods. Rainfall was not a major contributor, with only 3.2% and 2.9% originating from the Hebei and Beijing areas of the Bai River, respectively. Annually, the Bai River Basin exports loads of approximately 629.3 t.a˗1 of TN and 433.7 t.a˗1 of organic N (Org-N) from the Bai River Basin land to the river. The TN and Org-N loads at the final destination in the Miyun Reservoir were 521.3 t.a˗1 and 100.3 t.a˗1, respectively. Of the exported TN and Org-N, 17.16% and 76.87%, respectively, were retained in the river network. Consequently, N transformation occurred in the Bai River, with nitrification–denitrification being particularly dominant. Nitrification was more evident in the nitrate-enriched river. • Pollution risks persist in the Bai River during certain seasons. • Nitrification is more evident in the nitrate-enriched river. • Mainstream had a significant retention effect on the Organic N in the Bai River • Fertiliser is the dominant source of nitrate in the Bai River Basin [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]