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Large amounts of farmland have been converted from traditional cereal cropping to intensive vegetable cropping in China, creating environmental risks. Previous studies utilized several methods of estimating nitrate accumulation in soil and leaching to groundwater under intensive vegetable cultivation, such as comparing intensive cropping to non-intensive cropping, or investigating the seasonal dynamics of soil nitrates in the short term, such as 1 or 2 years. This study tried to utilize a different method, considering the effects of total nitrogen (N) input during the whole vegetable cropping phase (up to 9 years) after conversion from traditional cereal cropping on soil and groundwater. A large-scale investigation was performed in the study area. Vegetable, soil, and groundwater samples were collected from 22 fields. Results showed that soil nitrate was significantly correlated with total N input from chemical fertilizer during the whole vegetable cropping phase, and groundwater nitrate was significantly correlated with soil nitrate. Nitrate concentration in 45 % of wells exceeded the drinking water maximum contaminant level, 10 mg L −1 . These results suggest that soil nitrate accumulation in the area resulted from long-term application of large amounts of N chemical fertilizer, and not from manure. Furthermore, high irrigation levels caused the accumulated nitrate in soil to leach into the groundwater, resulting in nitrate contamination of the groundwater.

Excessive N fertilization in intensive agricultural areas of China has resulted in serious environmental problems because of atmospheric, soil, and water enrichment with reactive N of agricultural origin. This study examines grain yields and N loss pathways using a synthetic approach in 2 of the most intensive double-cropping systems in China: waterlogged rice/upland wheat in the Taihu region of east China versus irrigated wheat/rainfed maize on the North China Plain. When compared with knowledge-based optimum N fertilization with 30-60% N savings, we found that current agricultural N practices with 550-600 kg of N per hectare fertilizer annually do not significantly increase crop yields but do lead to about 2 times larger N losses to the environment. The higher N loss rates and lower N retention rates indicate little utilization of residual N by the succeeding crop in rice/wheat systems in comparison with wheat/maize systems. Periodic waterlogging of upland systems caused large N losses by denitrification in the Taihu region. Calcareous soils and concentrated summer rainfall resulted in ammonia volatilization (19% for wheat and 24% for maize) and nitrate leaching being the main N loss pathways in wheat/maize systems. More than 2-fold increases in atmospheric deposition and irrigation water N reflect heavy air and water pollution and these have become important N sources to agricultural ecosystems. A better N balance can be achieved without sacrificing crop yields but significantly reducing environmental risk by adopting optimum N fertilization techniques, controlling the primary N loss pathways, and improving the performance of the agricultural Extension Service.

Provisioning services, such as the production of food, feed, and fiber, have always been the main focus of agriculture. Since the 1950s, intensive cropping systems based on the cultivation of a single crop or a single cultivar, in simplified rotations or monocultures, and relying on extensive use of agrochemical inputs have been preferred to more diverse, self-sustaining cropping systems, regardless of the environmental consequences. However, there is increasing evidence that such intensive agroecosystems have led to a decline in biodiversity as well as threatening the environment and have damaged a number of ecosystem services such as the biogeochemical nutrient cycles and the regulation of climate and water quality. Consequently, the current challenge facing agriculture is to ensure the future of food production while reducing the use of inputs and limiting environmental impacts and the loss of biodiversity. Here, we review examples of multiple cropping systems that aim to use biotic interactions to reduce chemical inputs and provide more ecosystem services than just provisioning. Our main findings are the identification of underlying ecological processes and management strategies related to the provision of pairs of ecosystem services namely food production and a regulation service. We also found gaps between ecological knowledge and the constraints of agricultural practices in taking account of the interactions and possible trade-offs between multiple ecosystem services as well as socioeconomic constraints. We present guidelines for the design of multiple cropping systems combining ecological, agricultural, and genetic concepts and approaches.

Root and rhizosphere research has been conducted for many decades, but the underlying strategy of root/rhizosphere processes and management in intensive cropping systems remain largely to be determined. Improved grain production to meet the food demand of an increasing population has been highly dependent on chemical fertilizer input based on the traditionally assumed notion of ‘high input, high output’, which results in overuse of fertilizers but ignores the biological potential of roots or rhizosphere for efficient mobilization and acquisition of soil nutrients. Root exploration in soil nutrient resources and root-induced rhizosphere processes plays an important role in controlling nutrient transformation, efficient nutrient acquisition and use, and thus crop productivity. The efficiency of root/rhizosphere in terms of improved nutrient mobilization, acquisition, and use can be fully exploited by: (1) manipulating root growth (i.e. root development and size, root system architecture, and distribution); (2) regulating rhizosphere processes (i.e. rhizosphere acidification, organic anion and acid phosphatase exudation, localized application of nutrients, rhizosphere interactions, and use of efficient crop genotypes); and (3) optimizing root zone management to synchronize root growth and soil nutrient supply with demand of nutrients in cropping systems. Experiments have shown that root/rhizosphere management is an effective approach to increase both nutrient use efficiency and crop productivity for sustainable crop production. The objectives of this paper are to summarize the principles of root/rhizosphere management and provide an overview of some successful case studies on how to exploit the biological potential of root system and rhizosphere processes to improve crop productivity and nutrient use efficiency.

Intensive systems with two or three rice (Oryza sativa L.) crops per year account for about 50% of the harvested area for irrigated rice in Asia. Any reduction in productivity or sustainability of these systems has serious implications for global food security. Rice yield trends in the world’s longest-running long-term continuous cropping experiment (LTCCE) were evaluated to investigate consequences of intensive cropping and to draw lessons for sustaining production in Asia. Annual production was sustained at a steady level over the 50-y period in the LTCCE through continuous adjustment of management practices and regular cultivar replacement. Within each of the three annual cropping seasons (dry, early wet, and late wet), yield decline was observed during the first phase, from 1968 to 1990. Agronomic improvements in 1991 to 1995 helped to reverse this yield decline, but yield increases did not continue thereafter from 1996 to 2017. Regular genetic and agronomic improvements were sufficient to maintain yields at steady levels in dry and early wet seasons despite a reduction in the yield potential due to changing climate. Yield declines resumed in the late wet season. Slower growth in genetic gain after the first 20 y was associated with slower breeding cycle advancement as indicated by pedigree depth. Our findings demonstrate that through adjustment of management practices and regular cultivar replacement, it is possible to sustain a high level of annual production in irrigated systems under a changing climate. However, the system was unable to achieve further increases in yield required to keep pace with the growing global rice demand.

China is a large grain producer and consumer. Thus, obtaining information about the cropping intensity (CI) in cultivated land, as well as understanding the intensified utilization of cultivated land, is important to ensuring an increased grain production and food security for China. This study aims to detect and map the changes in CI over a period of 36 years across China’s core grain-producing area—the North China Plain (NCP)— using remotely sensed leaf area index (LAI) time series data acquired by the Global LAnd Surface Satellite (GLASS) products. We first selected 2132 sample points that consisted entirely, or almost entirely, of cultivated cropland from all pixels; the biennial LAI curves for the sample points were then extracted; the Savitzky–Golay filter and second-order difference algorithm were then applied to reconstruct the biennial LAI curves and obtain the number of peaks in these curves. In addition, the multiple cropping index (MCI) was calculated to represent the CI. Finally, the spatial distribution of the CI of cultivated land on the NCP was mapped from 1982 to 2018 using a geo-statistical kriging approach. Spatially, the results indicate that the CI of cultivated land over the NCP exhibits a distinct spatial pattern that conforms to “high in the south, low in the north”. The single cropping system (SCS) mainly occurred in the higher latitude area ranging from 37.04°N to 42.54°N, and the double cropping system (DCS) mainly existed in the lower latitude area between 31.95°N and 39.97°N. Temporally, the CI increased over the study period, but there were some large fluctuations in CI from 1982 to 1998 and it maintained relatively stable since 2000. Across the NCP, 68.14% of cultivated land experienced a significant increase in CI during the 36-year period, while only 3.87% showed a significant decrease. We also found that, between 1982 and 2018, the northern boundary of the area for DCS underwent a significant westward expansion and northward movement. Our results show a good degree of consistency with statistical data and previous research and also help to improve the reliability of satellite-based identification of CI using low spatial resolution LAI products. The results provide important information that can be used for analyzing and evaluating the rational utilization of cultivated land resources; thus, ensuring food security and realizing agricultural sustainability not only for the NCP, but for China as a whole. These results also highlight the value of satellite remote sensing to the long-term monitoring of cropping intensity at large scales.

Intensive cropping systems select for a low diversity of weeds tolerant of chemical control, leading to persistent weed‐crop competition and declining biodiversity. Crop rotation can mitigate this by introducing variable filters on the weed community through increasing management diversity. In this study, we investigate the effect of integrating livestock into no‐till crop rotations to complement chemical weed control. We analysed 12 years of weed seedbank data from a trial of eight rotation systems with different crop sequence diversities, of which four included grazed forage phases. Linear mixed models and ordination were used to assess how weed abundance, diversity, and community composition responded to management filters, defined in terms of levels of disturbance strength and diversity (grazing and herbicides), and resource availability and diversity (inorganic fertilizers, legumes, and manure). Grazed rotation systems had less herbicide applied than ungrazed rotation systems, and had the lowest weed abundance and highest weed diversity. Herbicides and grazing apply contrasting selection pressures on weeds, and this combination was more effective in reducing weed pressure than increasing herbicide quantity or mode‐of‐action diversity. Lower resource availability and higher nitrogen source diversity in grazed systems may have further reduced weed abundance and promoted diversity. Crop sequence diversity also reduced weed abundance and promoted weed diversity, indicating that variable crop‐weed interactions can enhance weed management. In addition, yields in the main cash crop (wheat) were highest where crop diversity was highest, regardless of whether the system contained grazed phases. Synthesis and applications. Diverse rotation systems produced high yields, and the inclusion of grazed forage phases maintained these yields at lower applications of herbicides and fertilizers: integrated livestock can therefore improve the sustainability of no‐till systems. The role of grazing as a filter imposing a contrasting selection pressure to other weed control options could be further explored to improve weed management in different farming systems. Diverse rotation systems produced high yields, and the inclusion of grazed forage phases maintained these yields at lower applications of herbicides and fertilizers: integrated livestock can therefore improve the sustainability of no‐till systems. The role of grazing as a filter imposing a contrasting selection pressure to other weed control options could be further explored to improve weed management in different farming systems.

Purpose Soil acidification from chemical N fertilization has worsened and is a major yield-limiting factor in the red soil (Ferralic Cambisol) of southern China. Assessment of the acidification process under field conditions over a long term is essential to develop strategies for maintaining soil productivity. The objective of this study was to quantify soil acidification rates from chemical fertilizers and determine the amount of manure needed to inhibit the acidification process. Materials and methods A long-term experiment with various fertilizations was carried out during 1990–2008 in a wheat–corn cropping system in the red soil of southern China. Treatments included non-fertilized control, chemical N only (N), chemical N and P (NP), chemical N, P and K (NPK), pig manure only (M), and NPK plus M (NPKM; 70 % total N from M). All N treatments had an input of 300 kg N ha −1  year −1 . Annual soil sampling was carried out for pH measurement and acidity analysis. Results and discussion Soil pH decreased sharply from an initial pH of 5.7 and then stabilized after 8 to 12 years of fertilization in the N, NP, and NPK treatments with a final pH of 4.2, 4.5, and 4.5, respectively. These three treatments significantly increased soil exchangeable acidity dominated by Al, decreased soil exchangeable base cations (Ca 2+ and Mg 2+ ), and elevated acidification rates (3.2–3.9 kmol H + ha −1  year −1 ). In contrast, the manure applications (M or NPKM) showed either an increase or no change in soil pH and increases in soil exchangeable base cations. Conclusions Urea application to the intensive cropping system accelerated acidification of the red soil during the 18-year field experiment. As 70 % or more total N source, continuous manure application can fully prevent or reverse red soil acidification process. As an effective animal waste management tool, manure incorporation into the acidic soil can promote the overall agricultural sustainability.

Purpose Biochar application is deemed to modify soil properties, but current research has been mostly conducted on the degraded land in tropical regions. Using six consecutive years of biochar field trial, we investigated effects of biochar on soil aggregates, structural stability, and soil organic carbon (SOC) and black C (BC) concentrations in aggregate fractions. The findings have important implications in managing soil structure and SOC sequestration in high fertility soils of the temperate areas. Materials and methods The study had four treatments: control; biochar rate at 4.5 (B4.5) and biochar rate at 9.0 t ha −1  year −1 (B9.0); and straw return (SR). Soil samples were collected from 0–10-cm layer, and aggregate size distribution was determined with the wet-sieving method. Then, the mean weight diameter (MWD) of aggregates and the aggregate ratio (AR), i.e., the ratio of the >250 μm to the 53–250 μm size were calculated to assess the structural stability. Total SOC and BC concentrations in bulk soil (<2 mm) and separated fractions (i.e., >2000, 250–2000, 53–250, and <53 μm) were measured. Results and discussion The B4.5 and B9.0 significantly increased macroaggregate (250–2000 μm) and MWD and AR indices relative to the control. Comparing to the SR, the improvements in soil aggregation under biochar treatments were limited. Additionally, more SOC in larger fractions (>2000, 250–2000, and 53–250 μm) and BC in extracted fractions under biochar soils were observed. These results implied that biochar addition enhanced both native SOC and BC physical protection by aggregation. Conclusions Biochar application is effective in mediating soil aggregation, and thus improves both native SOC and BC stabilization in an intensive cropping system of North China.

Addressing concerns about future food supply and climate change requires management practices that maximize productivity per unit of arable land while reducing negative environmental impact. Onfarm data were evaluated to assess energy balance and greenhouse gas (GHG) emissions of irrigated maize in Nebraska that received large nitrogen (N) fertilizer (183 kg of N·ha⁻¹) and irrigation water inputs (272 mm or 2,720 m³ ha⁻¹). Although energy inputs (30 GJ·ha⁻¹) were larger than those reported for US maize systems in previous studies, irrigated maize in central Nebraska achieved higher grain and net energy yields (13.2 Mg·ha⁻¹ and 159 GJ·ha⁻¹, respectively) and lower GHG-emission intensity (231 kg of CO₂e·Mg⁻¹ of grain). Greater input-use efficiencies, especially for N fertilizer, were responsible for better performance of these irrigated systems, compared with much lower-yielding, mostly rainfed maize systems in previous studies. Large variation in energy inputs and GHG emissions across irrigated fields in the present study resulted from differences in applied irrigation water amount and imbalances between applied N inputs and crop N demand, indicating potential to further improve environmental performance through better management of these inputs. Observed variation in N-use efficiency, at any level of applied N inputs, suggests that an N-balance approach may be more appropriate for estimating soil N₂O emissions than the Intergovernmental Panel on Climate Change approach based on a fixed proportion of applied N. Negative correlation between GHG-emission intensity and net energy yield supports the proposition that achieving high yields, large positive energy balance, and low GHG emissions in intensive cropping systems are not conflicting goals.