Effect of replacing synthetic nitrogen fertilizer with animal manure on grain yield and nitrogen use efficiency in China: a meta-analysis

Organic substitution enhances soil quality, soil microbial community stability, foxtail millet productivity, and grain quality in North China

Excessive use of chemical fertilisers has reduced crop productivity and adversely affected agroecosystems. Partial substitution of chemical fertilisers with organic fertilisers can sustainably increase cereal yields; however, its effect on soil microbial characteristics in foxtail millet fields remains unclear. A two-year (2022-2023) experiment was conducted to investigate the effects of four fertilisation regimes (chemical fertiliser only, CF; 25 % organic substitution, ZF25; 50 % organic substitution, ZF50; and 75 % organic substitution, ZF75) on foxtail millet productivity, soil quality, and soil microorganism properties. The organic substitution groups promoted plant nitrogen uptake by 4.16 %-10.09 % and 3.79 %-12.88 % and improved soil fertility, increasing the crop productivity index (CPI) by 7.46 %-12.79 % and 3.78 %-6.39 % and soil quality index (SQI) by 36.48 %-125.46 % and 12.04 %-87.25 % in 2022 and 2023, respectively, compared to that in the chemical fertiliser group. ZF25 and ZF50 increased the annual millet yield by 1.39 %-6.53 % in 2022 and 2.80 %-7.87 % in 2023 compared to that of CF. Organic substitution altered the structure of the soil bacterial and fungal communities. Compared with CF, the Shannon index of soil bacteria and fungi increased by 0.28 %-1.68 % and 8.88 %-14.10 %, respectively. The biomarkers enriched in the organic substitution and chemical fertiliser groups had similar associated soil biochemical metrics, but the associated trends were reversed. Organic substitution also improved soil carbon and nitrogen metabolism. Bacteria and fungi indirectly influenced yield variations via enzyme activity and nutrient interactions. This study has important theoretical implications for scientific fertiliser management and the development of microbial fertilisers in agricultural practice.

Synergetic Effect of Potassium, Biochar and Cattle Manure on the Growth and Yield of Maize, and Soil Physio-Chemical Characteristics

Biochar (BC) and cattle manure (CM) are carbon-nutrient-rich organic substances and have long been used to improve crop yield and soil fertility. Nevertheless, their combined effect with potassium (K) fertilizer remains unknown. Against the previous context, a 2-year (2021-2022) field experiment was conducted to assess the effect of K fertilization coupled with BC and CM on the growth and yield of maize and soil physio-chemical characteristics. The K application combined with BC and CM increased (p ≤ 0.05) the majority of the growth indices of maize crop compared with CK. Compared with CK, the combined application of K (60 kg K ha-1) with BC and CM resulted in an increased number of seeds cob-1 by up to 451 and 465, and up to 383 and 396, the 1000-seed weight up to 22 and 23 g, and up to 27 and 34 g, and the grain yield up to 1979 and 2900 and up to 3240 and 3341 kg ha-1, respectively, in 2021 and 2022. The integrated application of these inputs increased the chlorophyll of maize crops by 29 and 36% and by 30 and 44%, respectively, in 2021 and 2022. Such application also increased the photosynthetic activities of maize such as transpiration rate (Tr), stomatal conductance (Gs), and photosynthetic rate (Pn) by 21 and 23%, 143 and 110%, and by 64 and 66% in 2021 and by 19 and 30%, 163 and 118%, and by 63 and 72% in 2022. Similarly, the combined application of K, BC, and CM increased the K uptake of maize due to an increase in the soil extractable K. Equally, soil total N and organic matter improved under the combined application of K, BC, and CM. However, it did not affect the soil extractable P in 2021 but increased it in 2022. Conversely, these applications reduced (p < 0.05) the soil electrical conductivity, sodium adsorption ratio, and bulk density. This suggests that K fertilization combined with BC and CM enhances the growth and yield of maize by improving the soil nutrients availability, increasing soil organic matter, and enhancing soil structure and moisture retention.

Increasing silage maize yield and nitrogen use efficiency as a result of combined rabbit manure and mineral nitrogen fertilization

Combined application of organic and mineral fertilizers is crucial to obtaining high crop yields, increasing the utilization of nutrients by plants, and limiting their dispersion, thus protecting the environment, which underscores the importance of sustainable and minimally invasive agriculture. The aim of the field experiment was to determine the effect of application of rabbit manure (RM) and mineral nitrogen (Nmin) on the dry matter (DM) yield of maize and on nitrogen content, uptake, and use efficiency (NUE). RM application was tested at levels of 0, 20, 40 and 60 t·ha-1, and Nmin application at 0, 50, 100 and 150 kg·ha-1. Significant differences were noted in yield and in the content and uptake of nitrogen depending on both experimental factors. Increasing the application of RM and Nmin led to an increase in the yield of harvested maize and in the content and uptake of nitrogen. In terms of DM yield and nitrogen uptake (yield of crude protein), the most beneficial fertilizer variant was 60 t·ha-1 RM applied together with 100 kg·ha-1 Nmin. The highest NUE value was obtained following application of 20 t·ha-1 RM together with 150 kg·ha-1 Nmin.

A review of mitigation technologies and management strategies for greenhouse gas and air pollutant emissions in livestock production

One of the key issues in manure management of livestock production is to reduce greenhouse gas (GHG) and air pollutant emissions, which lead to significant environmental footprint and human/animal health threats. This study provides a review of potentially efficacious technologies and management strategies that reduce GHG and air pollutant emissions during the three key stages of manure management in livestock production, i.e., animal housing, manure storage and treatment, and manure application. Several effective mitigation technologies and practices for each manure management stage are identified and analyzed in detail, including feeding formulation adjustment, frequent manure removal and air scrubber during animal housing stage; solid-liquid separation, manure covers for storage, acidification, anaerobic digestion and composting during manure storage and treatment stage; land application techniques at appropriate timing during manure application stage. The results indicated several promising approaches to reduce multiple gas emissions from the entire manure management. Removing manure 2-3 times per week or every day during animal housing stage is an effective and simple way to reduce GHG and air pollutant emissions. Acidification during manure storage and treatment stage can reduce ammonia and methane emissions by 33%-93% and 67%-87%, respectively and proper acid, such as lactic acid can also reduce nitrous oxide emission by about 90%. Shallow injection of manure for field application has the best performance in reducing ammonia emission by 62%-70% but increase nitrous oxide emission. The possible trade-off brings insight to the prioritization of targeted gas emissions for the researchers, stakeholders and policymakers, and also highlights the importance of assessing the mitigation technologies across the entire manure management chain. Implementing a combination of the management strategies needs comprehensive considerations about mitigation efficiency, technical feasibility, local regulations, climate condition, scalability and cost-effectiveness.

Managing nitrogen for sustainable crop production with reduced hydrological nitrogen losses under a winter wheat-summer maize rotation system: an eight-season field study

Excessive nitrogen (N) application in wheat-maize cropping systems was adjusted towards more sustainable practices to reduce hydrological N losses while maintaining crop yield. In comprehensive quantification of N management effects on crop yield, N use efficiency (NUE), hydrological N losses, and soil nitrate residual across eight seasons, we have added to growing evidence of strategies beneficial for sustainable crop production with lower hydrological N losses. The results show that adjusted N practices enhanced crop yield and NUE, as compared to farmer's practices, but benefits varied with N rates and types. Optimized N treatment (OPT, 180 kg N ha-1 in both maize and wheat seasons) with or without straw returning produced the most crop yield. They increased maize yield by 5.5% and 7.3% and wheat yield by 6.2% and 3.2% on average, as compared to farmer's practice with huge N application (FP, 345 kg N ha-1 and 240 kg N ha-1 in maize and wheat). Regulation of N release through amendment with controlled release urea at a rate of 144 kg N ha-1 crop-1 (CRU treatment) obtained 4.4% greater maize yield than FP, and sustained a similar wheat yield with less N input, resulting in the highest crop NUE. Additionally, CRU was most effective in mitigating hydrological N loss, with 39.5% and 45.5% less leachate N and 31.9% and 35.9% less runoff N loss than FP in maize and wheat seasons. Synthetic N input correlated significantly and positively with runoff and leachate N losses, indicating it was one of the dominant factors driving hydrological N losses. Moreover, compared to OPT, additional straw returning (STR) or substituting 20% of the nutrients by duck manure (DMS) further reduced runoff N discharges due to the fact that organic matter incorporation increased resilience to rainfall. N over-application in FP caused considerable nitrate accumulation in the 0-90-cm soil profile, while the adjusted N practices, i.e., OPT, STR, CRU, and DMS treatments effectively controlled it to a range of 79.6-92.9 kg N ha-1. This study suggests that efforts using optimized N treatment integrated with CRU or straw returning should be encouraged for sustainable crop production in this region.