Replacing Synthetic Nitrogen Fertilizer with Different Types of Organic Materials Improves Grain Yield in China: A Meta-Analysis

Synthetic nitrogen fertilizer substitution (NSS) with different types of organic material is a cleaner agricultural practice for reducing the application of synthetic N input in farmlands while also relieving the environmental issues caused by the discharge of organic wastes. However, the effects of the NSS practice on crop yields, being the primary objective of agricultural activity, is still uncertain in China. This study conducted a meta-analysis to assess the impacts of the NSS practices with different types of organic materials on crop yields. Results showed that the average crop yield was increased by 3.4%, with significant differences under NSS, thereby demonstrating that this practice contributed to improving crop yields, especially of rice and maize. According to published reports, the NSS practices involving chicken manure, pig manure, and crop straw increased crop yields by 4.79, 7.68, and 3.28%, respectively, with significant differences, thus demonstrating the superior effects needed for replacing synthetic N fertilizer. Moreover, substitution ratios (SR) between 0% and 60% could be suggested when using the NSS practice, with the high SR recommended when the original soil fertility was adequate for crops. Considering the long-term effects of applied organic materials, improving the grain yield with the NSS practice should be expected in the long-term. By effectively applying the NSS, this study attempted to scientifically decide on the type of organic materials and the appropriate SR based on the conditions of the soil and the crop. The results provide research information for the development of clean agricultural production and food security in China.

174 Forage Production and Nutritive Value of Alfalfa-bermudagrass Mixtures Managed Under Contrasting Defoliation Strategies in the Southeast US

Incorporation of alfalfa (Medicago sativa) into bermudagrass pastures improves forage quality and decreases the reliance on synthetic nitrogen fertilizer. The objective of this study was to determine forage mass (FM), nutritive value (NV), and botanical composition of ‘Bulldog 805’ alfalfa and ‘Tifton 85’ bermudagrass (T85; Cynodon dactylon) mixtures managed under three defoliation strategies: 1) hay production (H), 2) grazing (G) or 3) dual-purpose (DP) use. The study was conducted in two locations (Headland, AL and Tifton, GA) using a randomized complete block design with two replicates. In spring 2020, grazed plots were divided in four strips and every 7-d, animals were rotated to a new strip and stocking rate was adjusted. Under DP, plots were grazed until mid-July, then forage was harvested in late August. For H plots, forage was harvested every 28 to 35-d. Forage samples were collected prior defoliation to determine FM and on grazed periods, pre- and post-grazing samples and disk meter measurements were collected. Nutritive value responses were determined using near-infrared spectroscopy. There was no effect of defoliation strategy on FM (P = 0.604; mean 3471 kg DM/ha). Greater FM (P = 0.002) was observed in July and August than June (3531 and 3976 vs 2905 kg DM ha-1, SE= 263). This response was associated with an up to 40% increase of T85 proportion in the mixture (P = 0.001). Alfalfa percentage was 78% greater for DP than G (P = 0.029). There were no differences among treatments for NV responses (P > 0.05). Among defoliation periods, crude protein, neutral detergent fiber and acid detergent fiber concentrations ranged from 14 to 22%, 45 to 58% and 28 to 35%, respectively. These preliminary results demonstrate multi-use options for this mixture in the region while aiming for increased forage nutritive value, and extended growing season, and sustainability of forage-livestock systems.

Ancient Relatives of Modern Maize From the Center of Maize Domestication and Diversification Host Endophytic Bacteria That Confer Tolerance to Nitrogen Starvation

Plants can adapt to their surroundings by hosting beneficial bacteria that confer a selective advantage in stressful conditions. Endophytes are a class of beneficial bacteria that exist within the internal spaces of plants and many species can improve plant nitrogen use efficiency. Nitrogen is an essential plant macronutrient, and is often a limiting factor to plant growth, especially in cereal crops such as maize. Every year farmers apply over 100 million metric tonnes of synthetic nitrogen fertilizer to meet the growing demand for stable food crops. Breeding efforts in maize over the past several decades has focused heavily on yield in response to nitrogen inputs, and so may have selected against adaptations that allow plants to survive in nitrogen stressed conditions. Data suggests that our heavy dependence on synthetic nitrogen fertilizer is not sustainable in the long term, and so there is on-going research efforts to reduce and replace this currently essential part of modern agriculture. Bacteria that improve plant tolerance to nitrogen stressed environments would allow farmers to reduce the amount of fertilizer they apply. The selection of maize under high nitrogen conditions to create modern varieties may have caused the plant to lose these beneficial bacteria that allowed wild maize ancestors to thrive in low nitrogen soil. Here in this study, we examine the root and shoot microbiomes of the wild ancestor of all maize, Parviglumis, and an ancient Mexican landrace (Mixteco) from Oaxaca, the area of early maize diversification. Both of these maize genotypes have thrived for thousands of years with little to no nitrogen inputs and so we hypothesized that they host beneficial bacteria that allow them to thrive in nitrogen stressed conditions. We identified multiple root endophyte species from each ancient maize relative that increased the growth of annual ryegrass (model maize relative) under nitrogen starvation. Furthermore, research infers these strains were vertically transmitted to new generations of plants, potentially through seed, indicating selection pressure for Parviglumis and Mixteco to maintain them in their microbiome.

The Effectiveness of Digestate Use for Fertilization in an Agricultural Cropping System

The need to find and maximize the use of alternative sources of nutrients for plants and soil environment have been on the forefront of research in sustainable agriculture. These alternatives have to be affordable, accessible, reproduceable, and efficient to compete with established inorganic fertilizers while at the same time reduce any potential negative impacts on the environment. We aimed to evaluate the effectiveness of digestate fertilization in an agricultural system over a period of three years. The digestate utilized in the study consisted of animal waste-based digestates, namely pig manure digestate, chicken manure digestate, and cow manure digestate, and were compared with synthetic nitrogen fertilizer. Every year, the digestate and the synthetic nitrogen fertilizer were split applied at the rate of 90 and 80 kg N ha−1. The soil chemical composition after three years of fertilization showed a slight decrease, significantly different nitrogen and carbon changes while phosphorus and potassium were significantly higher in the digestate treatments. The third year of digestate application showed higher grain yield than previous years and the yield from the digestate treatments were significantly different from the synthetic nitrogen fertilizer. The nitrogen use efficiency for the three years was in the range of 20–25 percent in the digestate treatments, with a strong correlation between the nitrogen use efficiency and the grain yield. There were varied results in the grain quality and straw quality in the digestate and synthetic nitrogen fertilizer with no clear trend observed. Our results showed a relatively high potential of animal waste digestates over the short to mid-term use with a positive result obtained in comparison to synthetic nitrogen fertilizer under favorable climatic conditions.

Greenhouse gas emissions in agricultural cultivated soils using animal waste-based digestates for crop fertilization

Agricultural waste contributes significantly to greenhouse gas (GHG) emissions if not adequately recycled and sustainably managed. A recurring agricultural waste is livestock waste that has consistently served as feedstock for biogas systems. The objective of this study was to assess the use of animal waste digestate to mitigate GHG emissions in agricultural fields. Wheat (Triticum spp. L.) was fertilized with different types of animal waste digestate (organic fertilizers) and synthetic nitrogen fertilizer (inorganic fertilizer). The 170 kg N/ha presented in digestates were split fertilized at an application rate of 90 and 80 kg N/ha. Emissions of GHGs (carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)) were monitored directly by a static chamber system. The soil and environmental variables were measured to determine their influence on GHG emissions. Emission peaks in N2O and CO2 after the first application of fertilizers with the emissions flattening out over the cultivating season while CH4 emission was negligible with no apparent patterns observed. Results showed individual and cumulative emissions of CO2, CH4 and N2O from the digestates were relatively low and digestate fertilization could be an efficient method for reducing GHGs from agricultural sources in temperate climate conditions.

Technological and institutional lock-in and excessive synthetic nitrogen fertilizer use on North American grain and oilseed farms

This intervention examines commodity grain and oilseed farmers’ over reliance on synthetic nitrogen fertilizer in North America. Most grain and oilseed farmers apply synthetic nitrogen fertilizer at rates higher than necessary in order to ensure maximum yields. At the same time, high fertilizer application rates lead to increased farm input expenses and generate significant amounts of water pollution and excessive greenhouse gas emissions. A number of low-cost alternative approaches have been developed which can significantly reduce or eliminate the need for synthetic nitrogen fertilizer while maintaining farm profitability. But such practices have only seen limited adoption by Canadian and US farmers. This is despite significant production cost savings and environmental benefits. A number technological and institutional factors work in combination to lock farmers into production models requiring large amounts of synthetic nitrogen fertilizer. They include crop varieties bred to thrive in artificially high nitrogen soil conditions, conventional tillage practices, restrictive financial arrangements, largely unenforced water quality laws, and non-diverse marketing outlets. These technological and institutional lock-ins are significant barriers to the adoption of alternative crop production practices that are less reliant upon synthetic nitrogen fertilizer.

The political economy of unsustainable lock-ins in North American commodity agriculture: a path forward – Response to Struckman

In this commentary, I argue that in North America, the overuse of synthetic nitrogen fertilizer is due to institutional and technological lock-ins, which are the result of historical policies with deep roots in an agricultural system focused on increasing production of commodities with disregard for their full social costs. Further, excessive fertilizer use is integral to production systems that have disconnected crop and livestock production to the extent that manure is a waste product, which further creates environmental problems. In order to address the environmental and social problems associated with industrial agriculture, it will be necessary to bring market prices closer to true social costs, thereby eliminating overproduction of commodity grains and oilseeds, and to promote more diverse agricultural landscapes.

Reduction of Synthetic Fertilizer for Sustainable Agriculture: Influence of Organic and Nitrogen Fertilizer Combination on Growth and Yield of Green Mustard

Organic fertilizer is capable to decrease the use of synthetic fertilizer due to release of plant nutrients and improvement of other soil properties. The objective of this experiment was to compare the growth and yield of green mustard as affected by cattle manure and litter compost. The experiment was conducted employing Completely Randomized Design with 8 treatments. Treatments included litter compost and cattle manure at rate of 25 Mg ha-1 and 15, 20, 25 Mg ha-1 with addition of 1.85 g nitrogen fertilizer per plant, respectively. Each treatment was replicated 5 times. Soil used in this experiment was Ultisol collected at depth of 0-20 cm. Five kg of soil was mixed with organic fertilizer according to each treatment and placed in 10 kg polybag. Green mustard was planted to each polybag. Nitrogen fertilizer was applied a week after planting. The experiment revealed that application of litter compost and cattle manure at rate 25 Mg ha-1 with additional nitrogen fertilizer resulted in higher green mustard fresh weight per plant and number of leaves. On the other hand, application of both organic fertilizers at rate of 25 Mg ha-1 without addition nitrogen fertilizer as other treatments did not provide significant differences on most variables observed. This indicated that application of organic fertilizer is able to reduce synthetic nitrogen fertilizer for green mustard production.