Co-benefits for net carbon emissions and rice yields through improved management of organic nitrogen and water.

Returning organic nutrient sources (for example, straw and manure) to rice fields is inevitable for coupling crop-livestock production. However, an accurate estimate of net carbon (C) emissions and strategies to mitigate the abundant methane (CH4) emission from rice fields supplied with organic sources remain unclear. Here, using machine learning and a global dataset, we scaled the field findings up to worldwide rice fields to reconcile rice yields and net C emissions. An optimal organic nitrogen (N) management was developed considering total N input, type of organic N source and organic N proportion. A combination of optimal organic N management with intermittent flooding achieved a 21% reduction in net global warming potential and a 9% rise in global rice production compared with the business-as-usual scenario. Our study provides a solution for recycling organic N sources towards a more productive, carbon-neutral and sustainable rice-livestock production system on a global scale.

Magnesium application reduced heavy metal-associated health risks and improved nutritional quality of field-grown Chinese cabbage.

Magnesium (Mg) is one of essential plant nutrients needed for optimal growth, yield and quality formation. Also, soil application of Mg fertilizer has been shown to be an effective approach to improve vegetable Mg nutrition. Leafy vegetables can accumulate relatively high levels of heavy metals in the above-ground plant parts. However, it remains unclear as to whether soil-applied Mg affects the vegetable nutritional quality and human health risk of heavy metals from field-grown Chinese cabbage. Here we conducted a two-year, two-crop cycle field experiment in south-western China to evaluate crop yield, vegetable nutrition and heavy metal accumulation in Chinese cabbage supplied with varying levels of Mg (0-90 kg ha-1). Soil application of Mg did not increase the cabbage yield. However, it did increase the vegetable vitamin C and water-soluble protein content by 20.0 % and 57.9 % with 45 and 22.5 kg Mg ha-1 application, respectively, compared to control. The nitrate content of Mg-supplied (45 kg ha-1) cabbages was significantly lower, by about 14 %, than the control. Further, it also significantly decreased the accumulation of cadmium and nickel in the above-ground tissues by reducing their uptake from soil to root or their translocation from root to shoot. Magnesium application, however, increased chromium uptake. A human health risks assessment nonetheless showed that the contribution of chromium from Mg-supplied plants to threshold hazard quotient and threshold carcinogenic risk were indeed much lower than that of cadmium and nickel, proving the value of crop Mg supplementation for ameliorating non-carcinogenic and carcinogenic risks to humans with the consumption of Chinese cabbage. Here we show that soil application of Mg in the range of 22.5-45 kg ha-1 to Chinese cabbage will significantly improve its nutritional qualities and alleviate the potential human health risks of heavy metals associated with Chinese cabbage consumption.

Innovative management programme reduces environmental impacts in Chinese vegetable production.

China produces half of the world's vegetables. The production uses 1.7% of the global harvest area of crops but accounts for 7.8% of the chemical fertilizers and 6.6% of crop-sourced greenhouse gas (GHG) emissions worldwide. Using an innovative management programme, the integrated knowledge and products strategy (IKPS), we demonstrate opportunities for producing more vegetables with lower environmental impacts in China's vegetable production systems. Combining soil-crop system management practices with enhanced-efficiency fertilizer products, IKPS was tested through 54 site-year field experiments in China's major agro-ecological zones by a national research network over 12 years. Compared with current farming practices, the adoption of IKPS decreased the nitrogen (N) application rate by 38%, N surplus by 65% and GHG emissions by 28%, while increasing yield by 17%. Scenario analyses showed that adoption of IKPS in China's vegetable production could mitigate resource and environmental burdens while enhancing food and nutrition security.

Nitrate leaching from open-field and greenhouse vegetable systems in China: a meta-analysis.

The potential for nitrate leaching in Chinese vegetable systems is substantial because of high inputs of nitrogen (N) fertilizer and water. To quantify the nitrate leaching and identify the key controlling factors in Chinese vegetable systems, we conducted a meta-analysis that included 221 data sets from 18 field studies. The results revealed that nitrate leaching over the entire crop growing season in Chinese vegetable systems was very high and averaged 79.1 kg N ha-1 and primarily resulted from extremely high N fertilizer inputs (in average 423 kg N ha-1). Nitrate leaching was, on the average, 63.9% greater in the greenhouse systems (98.0 kg N ha-1) than in open-field systems (59.8 kg N ha-1). The leaching factor, defined as the proportion of the quantity of N applied to soils that was lost due to nitrate leaching, averaged 14.6% overall and was significantly lower in greenhouse systems (10.9%) than in open-field systems (18.4%). This difference appears to be due to lower of the total water inputs (irrigation + precipitation) in greenhouse systems. Nitrate leaching increased with water input, the number of growing days, and the N rate. The nitrate leaching response to increasing N rate was linear. The leaching factor significantly increased with water input but was not affected by the N rate or the number of growing days. Compared with application of synthetic fertilizer alone, the application of manure alone or manure plus synthetic fertilizer significantly reduced both the nitrate leaching and the leaching factor in open-field and greenhouse systems. These results suggest that nitrate leaching in Chinese vegetable systems can be reduced by optimizing rates of N and water supply to synchronize crop needs. Application of mixed synthetic N fertilizer and manure is more effective in reducing nitrate leaching, compared to synthetic N only.

Nitrous oxide emissions in Chinese vegetable systems: A meta-analysis.

China accounts for more than half of the world's vegetable production, and identifying the contribution of vegetable production to nitrous oxide (N2O) emissions in China is therefore important. We performed a meta-analysis that included 153 field measurements of N2O emissions from 21 field studies in China. Our goal was to quantify N2O emissions and fertilizer nitrogen (N) based-emission factors (EFs) in Chinese vegetable systems and to clarify the effects of rates and types of N fertilizer in both open-field and greenhouse systems. The results indicated that the intensive vegetable systems in China had an average N2O emission of 3.91 kg N2O-N ha-1 and an EF of 0.69%. Although the EF was lower than the IPCC default value of 1.0%, the average N2O emission was generally greater than in other cropping systems due to greater input of N fertilizers. The EFs were similar in greenhouse vs. open-field systems but N2O emissions were about 1.4 times greater in greenhouses. The EFs were not affected by N rate, but N2O emissions for both open-field and greenhouse systems increased with N rate. The total and fertilizer-induced N2O emissions, as well as EFs, were unaffected by the type of fertilizers in greenhouse system under same N rates. In addition to providing basic information about N2O emissions from Chinese vegetable systems, the results suggest that N2O emissions could be reduced without reducing yields by treating vegetable systems in China with a combination of synthetic N fertilizer and manure at optimized economic rates.