Pursuing sustainable productivity with millions of smallholder farmers.

Sustainably feeding a growing population is a grand challenge, and one that is particularly difficult in regions that are dominated by smallholder farming. Despite local successes, mobilizing vast smallholder communities with science- and evidence-based management practices to simultaneously address production and pollution problems has been infeasible. Here we report the outcome of concerted efforts in engaging millions of Chinese smallholder farmers to adopt enhanced management practices for greater yield and environmental performance. First, we conducted field trials across China's major agroecological zones to develop locally applicable recommendations using a comprehensive decision-support program. Engaging farmers to adopt those recommendations involved the collaboration of a core network of 1,152 researchers with numerous extension agents and agribusiness personnel. From 2005 to 2015, about 20.9 million farmers in 452 counties adopted enhanced management practices in fields with a total of 37.7 million cumulative hectares over the years. Average yields (maize, rice and wheat) increased by 10.8-11.5%, generating a net grain output of 33 million tonnes (Mt). At the same time, application of nitrogen decreased by 14.7-18.1%, saving 1.2 Mt of nitrogen fertilizers. The increased grain output and decreased nitrogen fertilizer use were equivalent to US$12.2 billion. Estimated reactive nitrogen losses averaged 4.5-4.7 kg nitrogen per Megagram (Mg) with the intervention compared to 6.0-6.4 kg nitrogen per Mg without. Greenhouse gas emissions were 328 kg, 812 kg and 434 kg CO2 equivalent per Mg of maize, rice and wheat produced, respectively, compared to 422 kg, 941 kg and 549 kg CO2 equivalent per Mg without the intervention. On the basis of a large-scale survey (8.6 million farmer participants) and scenario analyses, we further demonstrate the potential impacts of implementing the enhanced management practices on China's food security and sustainability outlook.

Plastic pollution in croplands threatens long-term food security.

Plastic pollution is a global concern given its prevalence in aquatic and terrestrial ecosystems. Studies have been conducted on the distribution and impact of plastic pollution in marine ecosystems, but little is known on terrestrial ecosystems. Plastic mulch has been widely used to increase crop yields worldwide, yet the impact of plastic residues in cropland soils to soil health and crop production in the long term remained unclear. In this paper, using a global meta-analysis, we found that the use of plastic mulch can indeed increase crop yields on average by 25%-42% in the immediate season due to the increase of soil temperature (+8%) and moisture (+17%). However, the unabated accumulation of film residues in the field negatively impacts its physicochemical properties linked to healthy soil and threatens food production in the long term. It has multiple negative impacts on plant growth including crop yield (at the mean rate of -3% for every additional 100 kg/ha of film residue), plant height (-2%) and root weight (-5%), and soil properties including soil water evaporation capacity (-2%), soil water infiltration rate (-8%), soil organic matter (-0.8%) and soil available phosphorus (-5%) based on meta-regression. Using a nationwide field survey of China, the largest user of plastic mulch worldwide, we found that plastic residue accumulation in cropland soils has reached 550,800 tonnes, with an estimated 6%-10% reduction in cotton yield in some polluted sites based on current level of plastic residue content. Immediate actions should be taken to ensure the recovery of plastic film mulch and limit further increase in film residue loading to maintain the sustainability of these croplands.

Optimal Fertilizer Application Reduced Nitrogen Leaching and Maintained High Yield in Wheat-Maize Cropping System in North China.

Agricultural nitrogen (N) non-point source pollution in the North China Plain is a major factor that affects water quality and human health. The characteristics of N leaching under different N application conditions should be further quantified accurately in winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation farmland in North China, and a basis for reducing the risk and evaluation of N leaching in this area. A three-year field experiment was conducted using an in situ leakage pond method at a typical farmland in Henan in 2017-2020. Crop yield, soil nitrate N residues, and N utilization were also studied during the study period. Five N fertilizer rates were established with 0 (CK), 285 (LN), 465 (MN), 510 (MNO), and 645 (HN) kg N ha-1 for one rotation cycle. MNO was applied with chemical and organic fertilizers. The concentration of nitrate N in the soil leaching solution of CK, LN, MN, MNO, and HN was 0.81-, 1.49-, 3.65-, 5.55-, and 7.57-fold that of the World Health Organization's standard for underground drinking water. The exponential relationship between the N application rate and leaching was obtained when the annual N input exceeded 300 kg ha-1, and the N leaching rate increased greatly. The leaching rate of nitrate N in the total N was 50.6-82.4% under different treatments of N application. The combination of chemical and organic fertilizers treatment (MNO) reduced the amount of N that was leached in dry years. The nitrate leaching amount of summer maize accounts for 83.0%, 49.4%, and 72.0% of the total nitrate leaching amount of the whole rotation cycles in 2017-2020. LN and MN were recommended as the optimized N application here (285-465 kg N ha-1) with the two-season rotation grain yield of 17.2 ton ha-1 (16.5-17.9 ton ha-1) and nitrate N leaching of 21.6 kg ha-1 (12.6-30.5 kg ha-1).

Soil microbial community shifts with long-term of different straw return in wheat-corn rotation system.

Despite the integral role of the soil microbial community in straw decomposition, we still have a limited understanding of the complex response of microbial community to long-term of crop straw return in rotation system. Here we report on the structural and functional response of the soil bacterial and fungal community to more than 10 years of straw return in wheat-corn rotation system. Compared with single-season straw return, soil microbial phosphor lipid fatty acids (PLFAs) and catabolic activity were improved more greatly with double-season straw return. The relative abundance of bacteria and fungi decreased with double-season straw return, but increased with single-season straw return. The copiotrophic bacteria were more represented in the soils with corn straw return, while oligotrophic groups were more represented in soils with wheat straw return. Compared with wheat straw return, lower fungal community diversity and higher abundance of fungal pathogen (identified to be Leptosphaeria) were observed with corn straw return, especially at high return rates. Redundancy analysis showed that soil available potassium (P = 0.008) and ratio of C to N (P = 0.048) significantly affected the soil bacterial community, while soil electric conductivity (P = 0.04) was the significant factor impacting soil fungal community. It suggests that full corn straw return might have positive impact on soil mineral nutrient but negative impact on soil fungal community diversity and pathogenic risk, mainly due to the change in soil electric conductivity.

[Remediation of Cd/Ni Contaminated Soil by Biochar and Oxalic Acid Activated Phosphate Rock].

Taking soil contaminated with a combination of Cd and Ni as the research objective, biochar, and oxalic acid activated phosphate rock (APR) were applied both together and separately for the remediation of this contaminated soil. The effects of different ratios of amendments on the remediation of Cd and Ni heavy metals in the soil and on inorganic nitrogen and microbial biomass nitrogen (MBN) in the soil were compared. The results show that an increasing amount of biochar and APR, increases the soil pH gradually and acid-extractable Cd and Ni are gradually transformed into reducible, oxidable and residual Cd and Ni, resulting in a reduction in Cd and Ni bioavailability. After 40 days incubation, the acid extractable Ni decreased by 37.04% with a 14.8% increase in residual Ni, and acid extractable Cd decreased 40.28% with a 35.20% increase in residual Cd with the amendment of C50P3 (Applying 50 g·kg-1 biochar and 3 g·kg-1 APR) when compared to C0P0 treatment (Applying nothing). Furthermore, the MBN content for C50P0 (Applying 50 g·kg-1 biochar only) and C0P3 (Applying 3 g·kg-1 APR only) increased by 1.5 and 1 times, respectively, while the content of ammonium nitrogen decreased by 12.5% and 6.4%, respectively and the content of nitrate nitrogen decreased by 11.6% and 10.2%, respectively. This comparison shows that the combined effect of the application of biochar and APR is superior to each respective separate treatment. A mixture of 50 g·kg-1 of biochar and 3g·kg-1 of APR (C50P3) demonstrates the best effect on the remediation of the Cd and Ni in soil. Furthermore, the application of amendments promoted the transformation of inorganic nitrogen into organic nitrogen.

Harvesting more grain zinc of wheat for human health.

Increasing grain zinc (Zn) concentration of cereals for minimizing Zn malnutrition in two billion people represents an important global humanitarian challenge. Grain Zn in field-grown wheat at the global scale ranges from 20.4 to 30.5 mg kg-1, showing a solid gap to the biofortification target for human health (40 mg kg-1). Through a group of field experiments, we found that the low grain Zn was not closely linked to historical replacements of varieties during the Green Revolution, but greatly aggravated by phosphorus (P) overuse or insufficient nitrogen (N) application. We also conducted a total of 320-pair plots field experiments and found an average increase of 10.5 mg kg-1 by foliar Zn application. We conclude that an integrated strategy, including not only Zn-responsive genotypes, but of a similar importance, Zn application and field N and P management, are required to harvest more grain Zn and meanwhile ensure better yield in wheat-dominant areas.

Responses of Wheat Yield, Macro- and Micro-Nutrients, and Heavy Metals in Soil and Wheat following the Application of Manure Compost on the North China Plain.

The recycling of livestock manure in cropping systems is considered to enhance soil fertility and crop productivity. However, there have been no systematic long-term studies of the effects of manure application on soil and crop macro- and micro-nutrients, heavy metals, and crop yields in China, despite their great importance for sustainable crop production and food safety. Thus, we conducted field experiments in a typical cereal crop production area of the North China Plain to investigate the effects of compost manure application rates on wheat yield, as well as on the macro-/micro-nutrients and heavy metals contents of soil and wheat. We found that compost application increased the soil total N and the available K, Fe, Zn, and Mn concentrations, whereas the available P in soil was not affected, and the available Cu decreased. In general, compost application had no significant effects on the grain yield, biomass, and harvest index of winter wheat. However, during 2012 and 2013, the N concentration decreased by 9% and 18% in straw, and by 16% and 12% in grain, respectively. With compost application, the straw P concentration only increased in 2012 but the grain P generally increased, while the straw K concentration tended to decrease and the grain K concentration increased in 2013. Compost application generally increased the Fe and Zn concentrations in straw and grain, whereas the Cu and Mn concentrations decreased significantly compared with the control. The heavy metal concentrations increased at some compost application rates, but they were still within the safe range. The balances of the macro-and micro-nutrients indicated that the removal of nutrients by wheat was compensated for by the addition of compost, whereas the level of N decreased without the application of compost. The daily intake levels of micronutrients via the consumption of wheat grain were still lower than the recommended levels when sheep manure compost was applied, except for that of Mn.

[Assessment of groundwater vulnerability to nitrate in He'nan Province of China based on principal component regression].

According to the hydrological and morphological characteristics, He'nan Province was divided into mountainous region and plain region. The level of rich water, infiltration modulus of precipitation, fertilization level per unit area, proportions of vegetable planting area, and soil texture were selected as the common indices, and the slope and groundwater depth were selected as specific indices to assess the groundwater vulnerability to nitrate. Principal component regression analysis was adopted to determine the index weights, and the spatial distribution of groundwater vulnerability to nitrate in He'nan Province was assessed with ArcGIS 9.2. In the Province, the groundwater vulnerability to nitrate was mainly at low and medium level, and the region with this vulnerability level accounted for 68.4% of the total. The high vulnerability region accounted for 19.8%, and the extremely high vulnerability region occupied 11.8%. The main factors affecting the groundwater vulnerability to nitrate in plain region were soil texture, fertilization level, and infiltration modulus of precipitation, while those in mountainous region were fertilization level, soil texture, and slope. This study provided a theoretical basis for reasonable fertilization and agricultural environment management.

[Soil nutrient distribution and its relations with topography in Huangshui River drainage basin].

By using GIS and geostatistic techniques, this paper studied the spatial distribution patterns of soil nutrients and their relationships with topographic factors in Huangshui River drainage basin, a water source of Danjiangkou Reservoir. In the study area, the soil total nitrogen, total phosphorus, and organic matter varied spatially at medium level, with the variation coefficients being 51%, 66%, and 85%, respectively, whereas the soil available phosphorus displayed a strong spatial variation, with the variation coefficient reached 161%. The soil total nitrogen and organic matter exhibited a spatially positive autocorrelation, while the soil total and available phosphorus presented a spatially weak autocorrelation. Altitude was one of the main topographic factors affecting the spatial distribution patterns of the soil nutrients, having significant effects on the spatial distribution of total nitrogen, total phosphorus, and organic matter. Slope and profile curvature also had significant effects on the spatial distribution of the soil total nitrogen and organic matter. Based on these, the regression prediction models of topographic factors and soil nutrient spatial distribution were established, and the digital mappings of the soil nutrients were made, which provided data support for the precise management of soil resources in the study area.

[Nitrogen balance and its effects on nitrate-N concentration of groundwater in three intensive cropping systems of North China].

Selecting three main intensive cropping systems of North China, i.e., wheat-maize rotation, plastic greenhouse vegetable, and apple orchard as test objectives, this paper studied their nitrogen (N) budget, soil nitrate-N accumulation, and year-round dynamics of groundwater nitrate-N concentration. The results showed that in plastic greenhouse vegetable cropping system, the annual N input from chemical fertilizers, manure, and irrigation was 1358, 1881 and 402 kg x hm(-2), being 2.5, 37.5 and 83.8 folds of the corresponding items in wheat-maize cropping system, and 2.1, 10.4 and 68.2 folds in orchard, respectively, and its total N input amounted to 3656 kg x hm(-2), being 5.8 times of the wheat-maize cropping system, and 4.2 times of the orchard. The wet deposition N in the three cropping systems ranged from 14.2 kg x hm(-2) to 18.9 kg x hm(-2). The N output by wheat-maize, greenhouse vegetable and orchard was 280,329 and 121 kg x hm(-2), the N surplus was 349, 3327 and 746 kg x hm(-2), and the remained nitrate-N after harvest amounted to 221-275, 1173 and 613 kg x hm(-2) in 0-90 cm soil layer, and 213-242, 1032 and 976 kg x hm(-2) in 90-180 cm soil layer, respectively. Crop field had a comparatively even distribution of nitrate N in its 0-180 cm soil profile, and a sharp increase of nitrate N throughout the soil profile were found in both greenhouse vegetable and orchard fields. There was an evident nitrate leaching in all three cropping systems. The groundwater in shallow well (< 15 m) was severely contaminated in greenhouse vegetable area, with the nitrate-N concentration in 99% of the samples exceeding the maximum permissible limit for drinking water (10 mg x L(-1)), while 5% of the samples in deep well in vegetable area and in shallow well in orchard and 1% of the samples in deep well in wheat-maize field were exceeded the limit. The nitrate-N concentration exponentially decreased with well depth (m) in greenhouse vegetable area.