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Green manures (GM) combined with fertilizer reduction is an efficient measure to alleviate the environmental issues caused by the overapplication of chemical fertilizer. However, both the environmental and economic benefits remain unclear in coastal regions that are affected by both soil salinization and climate change. A field experiment was conducted in low-yield cropland in the Yellow River Delta to explore the effects of green manure rotation combined with fertilizer reduction on the soil environment and economic sustainability. Two GM species, Vicia villosa (HV) and Orychophragmus violaceus (OV), a traditional winter wheat (Wheat), were grown in winter, with a fallow control (Fallow). In the subsequent maize season, three fertilizer rate treatments, a full rate of 600 kg ha-1 compound fertilizer (F100), 85% of the full rate (F85), and 70% of the full rate (F70), were applied in each former treatment. The results indicated that GM return markedly increased soil total N (TN) and P (TP) before the V6 stage of maize (when maize had 6 leaves). The average TN contents of HV and OV increased by 56.9% and 38.5%, respectively, compared with that of Wheat, while the values for TP were 13.6% and 16.9%. Compared with Fallow, the maize yields of HV and OV increased by 25.6% and 13.8%, respectively, while that of Wheat decreased by 9.1%. The average partial fertilizer productivities (PFPs) for HV and OV increased by 25.3% and 14.0% compared with Fallow, while Wheat decreased by 8.9%. The PFPs for F85 and F70 increased by 19.4% and 37.7%, respectively, compared with F100. Reducing the fertilizer rate to 70% in the HV-maize rotation pattern did not reduce but increased the total net profit and rate of return. Thus, HV-maize rotation combined with 30% fertilizer reduction is suggested for sustainable agriculture in this region. [ABSTRACT FROM AUTHOR]

Background: Organic vegetable production has a demand for alternative fertilizers to replace fertilizers from sources that are not organic, that is, typically animal‐based ones from conventional farming. Aims: The aim of this study was to develop production strategies of plant‐based fertilizers to maximize cumulative nitrogen (N) production (equal to N yield by green manure crops), while maintaining a low carbon‐to‐nitrogen (C:N) ratio, and to test the fertilizer value in organic vegetable production. Methods: The plant‐based fertilizers consisted of the perennial green manure crops—alfalfa, white clover, red clover, and a mixture of red clover and ryegrass—and the annual green‐manure crops—broad bean, lupine, and pea. The crops were cut several times at different developmental stages. The harvested crops were used fresh or pelleted as fertilizers for field‐grown white cabbage and leek. The fertilizer value was tested with respect to biomass, N offtake, N recovery, and soil mineral N (Nmin). Poultry manure and an unfertilized treatment were used as controls. Results: The cumulative N production of the perennial green manure crops ranged from 300 to 640 kg N ha–1 year–1 when cut two to five times. The highest productions occurred at early and intermediate developmental stages, when cut three to four times. Annual green manure crops produced 110–320 kg N ha–1 year–1, since repeated cutting was restricted. The C:N ratio of the green manure crops was 8.5–20.5, and increased with developmental stage. The fertilizer value of green manure, as measured in white cabbage and leek, was comparable to animal‐based manure on the condition that the C:N ratio was low (<18). N recovery was 20%–49% for green manure and 29%–42% for poultry manure. A positive correlation was detected between soil Nmin and vegetable N offtake shortly after incorporating the green manure crops, indicating synchrony between N release and crop demand. Conclusions: Plant‐based fertilizers represent highly productive and efficient fertilizers that can substitute conventional animal‐based fertilizers in organic vegetable production. [ABSTRACT FROM AUTHOR]

Agriculture needs to reduce inputs of inorganic fertilizers and close the loop on nutrients that can otherwise become environmental pollutants. This can be achieved by promoting recycling of nutrients within the agricultural landscape. We investigated the extent to which plants found in riparian buffer zones have the potential to provide nutrients to crops as a green manure, through plant growth and decomposition studies. Under controlled conditions, species typical of Scottish riparian buffer strips were tested for their ability to accumulate biomass and nutrients in tissue under N‐ and P‐replete conditions and whether this ability enhanced the utility of the resulting green manure in promoting crop growth. In this proof‐of‐concept study, we found that green manure derived from riparian buffer strips did not effectively replace inorganic fertilizer and only had a significant positive effect on growth, yield, and nutrient accumulation in barley (Hordeum vulgare L.) when it was integrated with the addition of inorganic fertilizers. The individual species tested varied in the amount of P they accumulated in their tissue (1.38–52.73 mg P plant−1), but individual species did not differ in their ability to promote yield when used as a green manure. Our results indicate that selecting certain species in the buffer strip on the basis of their nutrient accumulating abilities is not an effective way to increase the utility of buffer strip green manure as a nutrient source for crops. Core Ideas: We need to close the loop on nutrients that become environmental pollutants.Green manure from riparian buffer strips cannot replace chemical fertilizers.Buffer strip green manure integrated with fertilizer promotes plant growth.Common riparian buffer species have variation in nutrient accumulation.Selection of P‐ and N‐accumulating plants does not provide a superior green manure. [ABSTRACT FROM AUTHOR]

Summer fallow results in inefficient precipitation use and could potentially be replaced with a green manure (GM) crop that reduces fertilizer N application. A 12-yr study on a Williams loam (fine-loamy, mixed, superactive, frigid Typic Argiustoll) was used to determine GM impacts on soil-N fertility, soil organic carbon (SOC), water use, yield, and water productivity (WP) of spring wheat (Triticum aestivum L.). Lentil (Lens culinaris Medikus cultivar Indianhead) was grown in rotation with nonfertilized spring wheat and killed either mechanically (GMMF) or chemically (GMCF). Inorganic N fertilizer treatments included annually cropped wheat (ACW), and wheat-fallow rotations (WFR) with mechanical (MF) or chemical (CF) fallow management. Low soil nitrate during the first 5 yr of the study resulted in a 33% decrease (P < 0.05) in wheat yield in GM compared to WFR. During the latter 6 yr, wheat yield differed by 2%, due to 26% greater spring soil nitrate (0-0.6 m) in GM than WFR, and growingseason change in nitrate N showed a 2.2-fold N-cycling advantage ofGM over WFR. Water use during nonwheat periods was similar in GM and WFRwhen lentil was killed at full bloom, but when grown to lower pod set GM used 20% more water than WFR. After 11 yr, SOC in the surface 15cm was 9.1% greater in treatments with chemical management than those with mechanical management. Green manure, with proper management, maintains WP and offsets fertilizer N needs after about three cropping cycles compared with traditional wheat-fallow rotations. [ABSTRACT FROM AUTHOR]

In this study, three types of cropping systems with different nutrient management strategies were studied on a clay soil with the aim of comparing leaching of N, P and K and obtaining knowledge on nutrient budgets. A conventional cropping system with cereals and application of mineral fertilizers (CON) was compared with two organic cropping systems, one without animal manure in which green manure crops were used for N supply (OGM) and one where animal manure (cattle slurry) was applied (OAM). Leaching and crop uptake of N, P and K, and soil mineral N were measured in pipe-drained plots over a 6-year period. The mean annual leaching loads of N were moderate and did not differ significantly ( P > 0.05) between treatments; 13 kg N ha−1 in CON, 11 kg N ha−1 in OGM and 7.4 kg N ha−1 in OAM. Average annual P leaching showed greater variation than N leaching and was significantly greater in OGM (0.81 kg ha−1 year−1) than in CON (0.36 kg ha−1) and OAM (0.41 kg ha−1). For all cropping systems, removal in harvested crops was the most important export of nutrients from the field and constituted between 80 and 94% of total N outputs (harvested and leached N). Yields of cereals in the organic systems were considerably less (15–50%) than in the CON system, leading to a less efficient use of N than in the conventional system. [ABSTRACT FROM AUTHOR]

Crop establishment, determined by shoot and root growth during early growth is a vital component in procuring desired plant populations and high yields in rainfed tropical smallholder farming systems, where green manures help maintain soil fertility and sustainability. As green manure incorporation could affect early seedling growth, studies were conduced in a plant house using soils from fields, to evaluate the impact of incorporating two popular tropical green manures (Crotalaria juncea and Tithonia diversifolia) into soil under rainfed field conditions over 3 years, on selected physico-chemical properties of the soils and on establishment and early shoot and root growth of maize (Zea mays), with and without inorganic fertilizers. In a given year, green manure was grown in one season while maize was grown in the other. A soil that did not receive green manures but was left fallow during the period of green manure cultivation was used as the control treatment. The incorporation of green manures over the 3 years showed trends of increasing soil physical properties, and also the available nitrogen, phosphorus and potassium contents. Incorporation of Crotalaria, with its higher nitrogen content, promoted shoot growth, while Tithonia induced the development of an extended root system. The use of inorganic fertilizers stimulated the beneficial impact of the green manures in promoting shoot and root growth. The use of green manures, especially Tithonia, promoted the development of seminal and nodal roots of maize seedlings, both in the form of length and thickness (based on root surface area) and root length densities, which could assist in successful crop establishment and resource utilization, rather than primary roots. The benefits of using green manures, especially Tithonia, in promoting root growth and Crotalaria in shoot development of maize seedlings even without inorganic fertilizers is presented. [ABSTRACT FROM AUTHOR]

Compares the annual leaching and crop uptake of N in arable cropping systems. Addition of green manures; Use of inorganic N fertilizer; Measurement of total N leaching load and crop N uptake.

Long term incubation studies to determine the nitrogen (N) mineralization rates and kinetics in soils freshly amended with some commonly used green manures such as Seshania rostrata, Gliricidia maculata, Leucaena leucocephala and Azolla pinnata are scarce. A long term aerobic study was, therefore, conducted by incubating soils freshly amended with the above-mentioned green manures in PVC columns at 35 ± 1°C and with 0.01 Mpa moisture content. The soils were then leached at periodic intervals for up to 36 weeks. The N-mineralization rates were greatest during the first week and decreased with time in all soils. The green manure amended soils leached 247 mg kg-1 more NO3 + NO2 - N than the unamended control. In general, the total N mineralized (mean 61%) was almost twice that of net N mineralized (mean 30%) in the amended soils. The percent N mineralized (total and net), however, varied with the nature of green manure incorporated into the soil. It was greatest in the soil amended with sesbania and lowest in the soil amended with azolla. The kinetic parameters derived using the double exponential model indicated that green manure amended soils possessed significantly higher N-mineralization potentials and rate constants compared to the unamended control. The kinetic parameters also varied with the nature of green manure incorporated into the soil. Among the various parameters lignin content, lignin to N ratio and lignin + polyphenol to N ratio of the green manures were the key factors governing the rate of decomposition and subsequent N mineralization from the amended soils. [ABSTRACT FROM AUTHOR]

Field experiments were conducted at Tamil Nadu Rice Research Institute, Aduthurai, India, during the wet seasons of 1992 and 1993 to study the effect of full and partial substitution of fertiliser N with green manure N (Sesbania rostrata) on nitrogen uptake, yield attributes and yield of rice. The experiment consisted of eight treatments with two levels of N (100 and 200 kg ha-1) and three sources of N application viz., fertilizer, integrated (1:1 fertilizer and green manure N) and green manure N compared to the recommended practice (150 kg fertilizer plus 6.25 t ha-1 (72 kg N) green manure) and a no N control. Nitrogen application markedly increased the N uptake. Combined use of the two N sources at 200 and 222 kg N ha-1 and of single fertilizer N at 200 kg N ha-1 recorded the maximum N uptake, increased the yield attributes such as number of panicles per unit area, weight per panicle, number of total and filled grains per panicle and test weight. At 200 kg N ha-1 full substitution of N by green manure reduced the grain yield but only partial substitution of N by green manure resulted in almost similar yield as single fertilizer N. Thus 200 kg N ha-1 applied in equal proportions of fertilizer and green manure N can be recommended for medium duration rice cultivars. [ABSTRACT FROM AUTHOR]