Nitrogen contribution of cowpea green manure and residue to upland rice

Cowpea, Vigna unguiculata (L.) Walp., is well adapted to acid upland soil and can be grown for seed, green manure, and fodder production. A 2-yr field experiment was conducted on an Aeric Tropaqualf in the Philippines to determine the effect of cowpea management practice on the response of a subsequent upland rice crop to applied urea. Cowpea was grown to flowering and incorporated as a green manure or grown to maturity with either grain and pods removed or all aboveground vegetation removed before sowing rice. Cowpea green manure accumulated on average 68 kg N ha⁻¹, and aboveground residue after harvest of dry pods contained on average 46 kg N ha⁻¹. Compared with a pre-rice fallow, cowpea green manure and residue increased grain yield of upland rice by 0.7 Mg ha⁻¹ when no urea was applied to rice. Green manure and residue substituted for 66 and 70 kg urea-N ha⁻¹ on upland rice, respectively. In the absence of urea, green manure and residue increased total aboveground N in mature rice by 12 and 14 kg N ha⁻¹, respectively. These increases corresponded to plant recoveries of 13% for applied green manure N and 24% for applied residue N. At 15 d after sowing rice (DAS), 33% of the added green manure N and 16% of the added residue N was recovered as soil (nitrate + ammonium)-N. At 30 DAS, the corresponding recoveries were 20 and 37% for green manure N and residue N, respectively. Cowpea cropping with removal of all aboveground cowpea vegetation slightly increased (p<0.05) soil (nitrate + ammonium)-N at 15 DAS as compared with the pre-rice fallow, but it did not increase rice yield. Cowpea residue remaining after harvest of dry pods can be an effective N source for a subsequent upland rice crop.     

Effects of carbonized and dried chicken manures on the growth, yield, and N content of soybean

The present study was conducted to investigate the effects of nitrogen derived from dried or carbonized chicken manure on growth, nodulation, yield and N content of soybean. ¹⁵N labeled chicken manure used in this study was obtained from the droppings of chicken fed on hulled rice grown under field conditions and fertilized with ¹⁵N-labeled stable isotope ammonium sulphate and potassium nitrate fertilizers. Carbonized chicken manure was made by heat treatment in a muffle furnace in our laboratory. This study was conducted in pots filled with clay loam soil. Results from the study show that the application of carbonized chicken manure increased soybean seed yield by 23% and 43% for the 50 and 100 kg N ha⁻¹ rates respectively. Dried chicken manure application increased soybean seed yield by 7% and 30% for the 50 and 100 kg N ha⁻¹ rates respectively. There was no difference in the N manure yield of both manures when applied at the same rate. The percentage ¹⁵N recovery was 17.6% and 8.9% for carbonized chicken manure, 19.2% and 10.5% for dried chicken manure at 50 and 100 kg N ha⁻¹ rates respectively at peak flowering stage of soybean growth. We found high total nitrogen yields of soybean at the rate of 100 kg N ha⁻¹ for both manures. There was a positive relationship between number of nodules and seed yield of soybean. Total N content also showed positive relationship with number of nodules and seed yield of soybean. We supposed that the higher P content of carbonized chicken manure is responsible for the higher seed yield and nodule growth compared to dried chicken manure.     

Biochar application to rice with 15N-labelled fertilizers,enhanced leaf nitrogen concentration and assimilation by improving morpho-physiological traits and soil quality

Leaf nitrogen (N) concentration plays an important role in biochemical and physiological functions, and N availability directly influences rice yield. However, excessive N fertilization is considered to be a root cause of environmental issues and low nitrogen use efficiency. Therefore, the selection of appropriate nutrient management practices and organic amendments is key to maximizing nitrogen uptake and maintaining high and sustainable rice production. Here, we evaluated the effects of different ¹⁵N-labelled nitrogen sources (urea, ammonium nitrate, and ammonium sulfate at 315 kg ha⁻¹) with or without biochar (30 t ha⁻¹) on paddy soil properties, root growth, leaf gas exchange, N metabolism enzymes, and N uptake in the early and late seasons of 2019. We found significant differences among N fertilizer sources applied with or without biochar (P < 0.05). Across the seasons, the combination of biochar with N fertilizers significantly increased soil organic carbon by 51.21% and nitrogen availability by 27.51% compared with N fertilizers alone. Correlation analysis showed that rice root morphological traits were strongly related to soil chemical properties, and higher root growth was measured in the biochar treatments. Similarly, net leaf photosynthetic rate averaged 9.34% higher, chlorophyll (Chl) a concentration 12.91% higher, and Chl b concentration 10.05% higher in the biochar treatments than in the biochar-free treatments across the seasons. Notably, leaf ¹⁵N concentration was 23.19% higher in the biochar treatments in both seasons. These results illustrated higher activities of N metabolism enzymes such as NR, GS, and GOGAT by an average 23.44%, 11.26% and 18.16% in the biochar treatments across the seasons, respectively. The addition of biochar with synthetic N fertilizers is an ecological nutrient management strategy that can increase N uptake and assimilation by ameliorating soil properties and improving the morpho-physiological factors of rice.     

The fate of15N-labelled organic nitrogen in sheep manure applied to soils of different texture under field conditions

The fate of nitrogen from¹⁵N-labelled sheep manure and ammonium sulfate in small lysimeters and plots in the field was studied during two growth seasons. In April 1991,¹⁵N-labelled sheep faeces (87 kg N ha^–1) plus unlabelled (NH₄)₂SO₄ (90 kg N ha^–1), and (¹⁵NH₄)₂SO₄ (90 kg N ha^–1) were each applied to three soils; soil 1 (100% soil + 0% quartz sand), soil 2 (50% soil + 50% quartz sand) and soil 3 (25% soil + 75% quartz sand). The lysimeters were cropped with spring barley (Hordeum vulgare L.) and undersown ryegrass (Lolium perenne L.). The barley crop recovered 16–17% of the labelled manure N and 56% of the labelled (NH₄)₂SO₄-N. After 18 months 30% of the labelled manure N and 65% of the labelled (NH₄)₂SO₄-N were accumulated in barley, the succeeding ryegrass crop and in leachate collected below 45 cm of soil, irrespective of the soil-sand mixture. Calculating the barley uptake of manure N by difference of N uptake between manured and unmanured soils, indicated that 4%, 10% and 14% of the applied manure N was recovered in barley grown on soil-sand mixtures with 16%, 8% and 4% clay, respectively. The results indicated that the mineralization of labelled manure N was similar in the three soil-sand mixtures, but that the manure caused a higher immobilization of unlabelled ammonium-N in the soil with the highest clay content. Some of the immobilized N apparently was remineralized during the autumn and the subsequent growth season. After 18 months, 11–19% of the labelled manure N was found in the subsoil (10–45 cm) of the lysimeters, most of this labelled N probably transported to depth as organic forms by leaching or through the activities of soil fauna. In unplanted soils 67–74% of the labelled manure N was recovered in organic form in the 0–10 cm soil layer after 4 months, declining to 55–64% after 18 months. The lowest recovery of labelled N in top-soil was found in the soil-sand mixture with the lowest clay content. The mass balance of¹⁵N showed that the total recovery of labelled N was close to 100%. Thus, no significant gaseous losses of labelled N occurred during the experiment.     

Integrated effects of organic,inorganic and biological amendments on methane emission,soil quality and rice productivity in irrigated paddy ecosystem of Bangladesh: field study of two consecutive rice growing seasons

Aims

Effects of different soil amendments were investigated on methane (CH₄) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh.

Methods

The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha^?1) + rice straw compost (2 t ha^?1) as a control, urea (170 kg ha^?1) + rice straw compost (2 t ha^?1) + silicate fertilizer, urea (170 kg ha^?1) + sesbania biomass (2 t ha^?1 ) + silicate fertilizer, urea (170 kg ha^?1) + azolla biomass (2 t ha^?1) + cyanobacterial mixture 15 kg ha^?1 silicate fertilizer, urea (170 kg ha^?1) + cattle manure compost (2 t ha^?1) + silicate fertilizer.

Results

The average of two growing seasons CH₄ flux 132 kg ha^?1 was recorded from the conventional urea (220 kg ha^?1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH₄ flux ha^?1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha^?1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha^?1) in paddy field.

Conclusion

Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH₄ emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh.     

豆科绿肥及施氮量对旱地麦田土壤主要肥力性状的影响

通过2a田间定位试验,研究渭北旱塬地区夏闲期插播并翻压不同豆科绿肥(长武怀豆、大豆和绿豆)以及小麦生长季不同施氮量(0,108,135,162 kg/hm2)对麦田土壤肥力性状的影响,以期为提高旱地土壤质量提供理论依据.试验结果表明:(1)种植豆科绿肥能显著提高土壤有机质、活性有机质和全氮含量,增加土壤碳库管理指数(CPMI),对土壤速效钾含量没有显著影响;(2)绿豆还田量高于长武怀豆和大豆,然而土壤培肥效果逊于长武怀豆和大豆;(3)夏闲期种植绿肥明显消耗了土壤水分,导致绿肥翻压前、小麦播前直至收获后,0-200 cm土壤贮水量显著低于休闲处理,但耗水量与休闲没有明显差异,由于小麦产量显著增加,因此豆科绿肥显著提高了水分生产效率;(4)与不施氮相比,小麦生长季施用氮肥能显著增加土壤水分生产效率,却对土壤各肥力性状的影响均不显著.夏闲期种植并翻压豆科绿肥是旱地培肥土壤、提高水分生产效率的有效途径.     

Improving Quantitative and Qualitative Characteristics of Wheat (<i>Triticum aestivum</i> L.) through Nitrogen Application under Semiarid Conditions

Nitrogen (N), the building block of plant proteins and enzymes, is an essential macronutrient for plant functions. A field experiment was conducted to investigate the impact of different N application rates (28, 57, 85, 114, 142, 171, and 200 kg ha⁻¹) on the performance of spring wheat (cv. Ujala-2016) during the 2017–2018 and 2018–2019 growing seasons. A control without N application was kept for comparison. Two years mean data showed optimum seed yield (5,461.3 kg ha⁻¹) for N-application at 142 kg ha⁻¹ whereas application of lower and higher rates of N did not result in significant and economically higher seed yield. A higher seed yield was obtained in the 2017–2018 (5,595 kg ha⁻¹) than in the 2018–2019 (5,328 kg ha⁻¹) growing seasons under an N application of 142 kg ha⁻¹. It was attributed to the greater number of growing degree days in the first (1,942.35°C days) than in the second year (1,813.75°C). Higher rates of N (171 and 200 kg ha⁻¹) than 142 kg ha⁻¹ produced more number of tillers (i.e., 948,300 and 666,650 ha⁻¹, respectively). However, this increase did not contribute in achieving higher yields. Application of 142, 171, and 200 kg ha⁻¹ resulted in 14.15%, 15.0% and 15.35% grain protein concentrations in comparison to 13.15% with the application of 114 kg ha⁻¹. It is concluded that the application of N at 142 kg ha⁻¹ could be beneficial for attaining higher grain yields and protein concentrations of wheat cultivar Ujala-2016.

     

Nutrient constraints to tropical agroecosystem productivity in long‐term degrading soils

Soil degradation is one of the most serious threats to sustainable crop production in many tropical agroecosystems where extensification rather than intensification of agriculture has occurred. In the highlands of western Kenya, we investigated soil nitrogen (N) and phosphorus (P) constraints to maize productivity across a cultivation chronosequence in which land‐use history ranged from recent conversion from primary forest to 100 years in continuous cropping. Nutrient treatments included a range of N and P fertilizer rates applied separately and in combination. Maize productivity without fertilizer was used as a proxy measure for indigenous soil fertility (ISF). Soil pools of mineral nitrogen, strongly bound P and plant‐available P decreased by 82%, 31% and 36%, and P adsorption capacity increased by 51% after 100 years of continuous cultivation. For the long rainy season (LR), grain yield without fertilizer declined rapidly as cultivation age increased from 0 to 25 years and then gradually declined to a yield of 1.6 Mg ha^?1, which was maintained as time under cultivation increased from 60 to 100 years. LR grain yield in the old conversions was only 24% of the average young conversion grain yield (6.4 Mg ha^?1). Application of either N or P alone significantly increased grain yield in both the LR and short rainy (SR) seasons, but only application of 120 kg N ha^?1 on the old conversion increased yield by >1 Mg ha^?1. In both SR and LR, there was a greater average yield increment response to N and P when applied together (ranging from 1 to 3.8 Mg ha^?1 for the LR), with the greatest responses on the old conversions. The benefit–cost ratio (BCR) for applying 120 kg N ha^?1 alone was <1 except on the old conversions, while BCRs were>1 for applying 25 kg P ha^?1 alone at all levels of conversion for both seasons. Application of both N (120 kg N ha^?1) and P (25 kg P ha^?1) on the old conversions resulted in the greatest BCRs. This study clearly indicates that maize productivity responses to N and P fertilizer are significantly affected by the age of cultivation and its influence on ISF, but that loss of productivity can be restored rapidly when these limiting nutrients are applied. Management strategies should consider ISF and economic factors to determine optimal N and P input requirements for achieving and sustaining profitable crop production on degraded soils.     

Reversibility of Soil Productivity Decline with Organic Matter of Differing Quality Along a Degradation Gradient

In the highlands of Western Kenya, we investigated the reversibility of soil productivity decline with increasing length of continuous maize cultivation over 100 years (corresponding to decreasing soil organic carbon (SOC) and nutrient contents) using organic matter additions of differing quality and stability as a function of soil texture and inorganic nitrogen (N) additions. The ability of additions of labile organic matter (green and animal manure) to improve productivity primarily by enhanced nutrient availability was contrasted with the ability of stable organic matter (biochar and sawdust) to improve productivity by enhancing SOC. Maize productivity declined by 66% during the first 35 years of continuous cropping after forest clearing. Productivity remained at a low level of 3.0 t grain ha^-1 across the chronosequence stretching up to 105 years of continuous cultivation despite full N–phosphorus (P)–potassium (K) fertilization (120–100–100 kg ha⁻¹). Application of organic resources reversed the productivity decline by increasing yields by 57–167%, whereby responses to nutrient-rich green manure were 110% greater than those from nutrient-poor sawdust. Productivity at the most degraded sites (80–105 years since forest clearing) increased in response to green manure to a greater extent than the yields at the least degraded sites (5 years since forest clearing), both with full N–P–K fertilization. Biochar additions at the most degraded sites doubled maize yield (equaling responses to green manure additions in some instances) that were not fully explained by nutrient availability, suggesting improvement of factors other than plant nutrition. There was no detectable influence of texture (soils with either 11–14 or 45–49% clay) when low quality organic matter was applied (sawdust, biochar), whereas productivity was 8, 15, and 39% greater (P < 0.05) on sandier than heavier textured soils with high quality organic matter (green and animal manure) or only inorganic nutrient additions, respectively. Across the entire degradation range, organic matter additions decreased the need for additional inorganic fertilizer N irrespective of the quality of the organic matter. For low quality organic resources (biochar and sawdust), crop yields were increasingly responsive to inorganic N fertilization with increasing soil degradation. On the other hand, fertilizer N additions did not improve soil productivity when high quality organic inputs were applied. Even with the tested full N–P–K fertilization, adding organic matter to soil was required for restoring soil productivity and most effective in the most degraded sites through both nutrient delivery (with green manure) and improvement of SOC (with biochar).     

Green manure technology: Potential,usage, and limitations. A case study for lowland rice

The growing concern about the sustainability of tropical agricultural systems stands in striking contrast to a world-wide decline in the use of soil-improving legumes. It is timely to assess the future role that soil-improving legumes may play in agricultural systems. This paper reviews recent progress, potential, and limitations of green manure technology, using lowland rice cropping systems as the example.Only a few legume species are currently used as green manures in lowland rice. Sesbania cannabina is the most widely used pre-rice green manure for rice in the humid tropics of Africa and Asia. Astragalus sinicus is the prototype post-rice green manure species for the cool tropics. Stem-nodulating S. rostrata has been most prominent in recent research. Many green manure legumes show a high N accumulation (80–100 kg N ha^-1 in 45–60 days of growth) of which the major portion (about 80%) is derived from biological N₂ fixation. The average amounts of N accumulated by green manures can entirely substitute for mineral fertilizer N at current average application rates. With similar N use efficiencies, green manure N is less prone to loss mechanisms than mineral N fertilizers and may therefore contribute to long-term residual effects on soil productivity.Despite a high N₂-fixing potential and positive effects on soil physical and chemical parameters, the use of green manure legumes for lowland rice production has declined dramatically world-wide over the last 30 years. Land scarcity due to increasing demographic pressure and a relatively low price of urea N are probably the main determining factors for the long-term reduction in pre-rice green manure use. Post-rice green manures were largely substituted for by high-yielding early-maturing grain legumes. Unreliability of green manure performance, non-availability of seeds, and labor intensive operations are the major agronomic constraints. The recognition and extrapolation of niches where green manures have a comparative advantage may improve an often unfavorable economic comparison of green manure with cash crop or fertilizer N. Socio-economic factors like the cost of land, labor, and mineral N fertilizer are seen to determine the cost-effectiveness and thereby farmers' adoption of sustainable pre-rice green manure technology. Hydrology and soil texture determine the agronomic competitiveness of a green manure with N fertilizers and with alternative cash crops. In general, the niches for pre-rice green manure are characterized by a relatively short time span available for green manure growth and a soil moisture regime that is unfavorable for cash crops (flood-prone rainfed lowlands with coarse-textured soils).Given the numerous agronomic and socio-economic constraints, green manure use is not seen to become a relevant feature of favourable rice-growing environments in the foreseeable future. However, in environments where soil properties and hydrology are marginal for food crop production, but which farmers may be compelled to cultivate in order to meet their subsistence food requirements, green manures may have a realistic and applicable potential.     

The Effects of Land-use History on Soil Properties and Nutrient Dynamics in Northern Hardwood Forests of the Adirondack Mountains

Soil nutrient pools and nitrogen dynamics in old-growth forests were compared with selectively logged stands and stands that were selectively logged and then burned approximately 100 years ago to test the hypothesis that land-use history exerts persistent controls on nutrient capital and nitrogen (N) transformation rates. We provide estimates of net N mineralization and nitrification rates for old-growth forests from the northeastern United States, a region in which few old-growth forests remain and for which few published accounts of mineralization rates exist. At the plot level, no effects of the dominant tree species were observed on any measured soil properties or N-cycling rates. Effects of alternate disturbance histories were detected in soil carbon (C) and N pools. Old-growth forest soils had higher total C (67 Mg·ha^–1) and N capital (3.3 Mg·ha^–1) than that of historically logged then burned soils (C = 50 Mg·ha^–1 and N = Mg·ha^–1), with intermediate values (C = 54 Mg·ha^–1 and N = 2.7 Mg·ha^–1) in the stands that were historically logged. Despite these differences in C and N content, corresponding differences in C–N ratio, net N mineralization rates, and net nitrification rates were not observed. The N concentration in the green foliage of American beech trees (Fagus grandifolia) was also highest from canopy trees growing in old-growth stands (3.0%), followed by logged stands (2.6%), and lowest in the logged/burned stands (2.2%). These data suggest that some legacies of light harvesting on ecosystem processes may be detected nearly 100 years following the disturbance event. These results are discussed in the context of how multiple forest disturbances act in concert to affect forest dynamics.     

Poultry Manure as an Organic Fertilizer with or without Biochar Amendment: Influence on Growth and Heavy Metal Accumulation in Lettuce and Spinach and Soil Nutrients

This pot-based study investigated the influence of poultry manure and 1:1 mixture of poultry manure + biochar (produced from farmyard manure [FYM] or wood), on the biomass production and concentration of heavy metals in leaves of lettuce and spinach. The concentration of mineral nitrogen (N) and soluble inorganic phosphorus (P) of soils cultivated with these vegetables was also investigated. The application of poultry manure or FYM biochar in soil as 10% (equivalent to 60 t ha^–1 , an estimated 1726.8 kg ha^–1 N in poultry manure and 1353.9 kg ha^–1 N in FYM) and 15% amendment (equivalent to 90 t ha^–1 , an estimated 2590.2 kg ha^–1 N in poultry manure and 2030.8 kg ha^–1 N in FYM) significantly decreased biomass production of lettuce as compared to control (no fertilizer added) treatment. However, mixture of poultry manure with wood-derived biochar at both application rates (i.e., 10% and 15%) and with FYM biochar at lower application rate (i.e., 10%) caused 2–3-fold increase in aboveground plant biomass and 2–14-fold increase in root biomass (p < 0.05). Furthermore, as compared to control treatment, a significant ~2–3-fold increase in aboveground plant biomass was also observed in response to mixture of poultry manure with wood-derived and FYM derived biochars at 10% amendment rates. As compared to control treatment, concentration of mineral N and soluble inorganic P were higher in soils of all other treatments. In spinach, amendment of poultry manure or its co-amendment with biochar of FYM significantly increased aboveground plant biomass at 7% (equivalent to 42 t ha^–1 ) as compared to 3% and 5% amendment rates (equivalent to 18 and 30 t ha^–1 respectively). The concentration of soil mineral N and soil soluble mineral P was not different between treatments. In lettuce, wood-derived biochar did not reduce concentration of heavy metals (i.e., manganese (Mn), copper (Cu), iron, (Fe), cadmium (Cd), lead (Pb), nickel (Ni) and cobalt (Co) than FYM-derived biochar while in spinach, as compared to poultry manure, co-amendment of poultry manure with wood-derived biochar reduced concentration of heavy metals, indicating differential responses of crops to organic amendments.     

Effect of rainfall pattern on nitrogen mineralization and leaching in a green manure experiment in South Rwanda

The effects of green manures, sorghum residues and farmyard manure on N dynamics and crop yields were studied during three dry and wet seasons on a Typic Sombriudox in South Rwanda. In addition, a resin core study was conducted within a 4-year green manure field experiment to follow the seasonal pattern of N mineralization and leaching after application of residues from Tephrosia vogelii, Sorghum bicolor, a mixture of both materials, and farmyard manure.During the dry season, topsoil (0–20 cm) mineral N remained constant. At the beginning of the wet season, the rainfall pattern determined N availability. With low rainfall intensities a mineralization flush occurred, doubling topsoil mineral N concentrations within 5 days after wetting. In contrast, under heavy rains at the onset of the rainy season, topsoil mineral N decreased by 50–70% within the first two weeks.The application of organic fertilizers has a strong influence on N availability, but the effects can be negated by heavy rainfall. Incorporation of leaves from Tephrosia vogelii (2.7 t dm ha^-1) and farmyard manure (7 t dm ha^-1) doubled the mineralization flush after the first rains. During the rest of the wet season, N release by the green manure was small, whereas the farmyard manure was found to mobilize N after a period of N immobilization. Incorporation of sorghum residues had only a small effect, while mixing the straw with green and farmyard manure immobilized N temporarily.Nitrogen leaching, measured by exchange resins at a depth of 20 cm, was increased up to 50% by the incorporation of green and farmyard manure. This points to rapid N translocation of easily mineralizable N. The additional incorporation of sorghum residues reduced N leaching of both materials significantly. Since rainfall is often unpredictable, the synchronization of N released from crop residues with crop N demand may require additional management practices.     

Nitrogen-15 balances for urea and neem coated urea applied to lowland rice following two cowpea cropping systems

Little is known about whether the high N losses from inorganic N fertilizers applied to lowland rice (Oryza sativa L.) are affected by the combined use of either legume green manure or residue with N fertilizers. Field experiments were conducted in 1986 and 1987 on an Andaqueptic Haplaquoll in the Philippines to determine the effect of cowpea [Vigna unguiculata (L.) Walp.] cropping systems before rice on the fate and use efficiency of¹⁵N-labeled, urea and neem cake (Azadirachta indica Juss.) coated urea (NCU) applied to the subsequent transplanted lowland rice crop. The pre-rice cropping systems were fallow, cowpea incorporated at the flowering stage as a green manure, and cowpea grown to maturity with subsequent incorporation of residue remaining after grain and pod removal. The incorporated green manure contained 70 and 67 kg N ha⁻¹ in 1986 and 1987, respectively. The incorporated residue contained 54 and 49 kg N ha⁻¹ in 1986 and 1987, respectively. The unrecovered¹⁵N in the¹⁵N balances for 58 kg N ha⁻¹ applied as urea or NCU ranged from 23 to 34% but was not affected by pre-rice cropping system. The partial pressure of ammoniapNH₃, and floodwater (nitrate + nitrite)-N following application of 29 kg N ha⁻¹ as urea or NCU to 0.05-m-deep floodwater at 14 days after transplanting was not affected by pre-rice cropping system. In plots not fertilized with urea or NCU, green manure contributed an extra 12 and 26 kg N ha⁻¹, to mature rice plants in 1986 and 1987, respectively. The corresponding contributions from residue were 19 and 23 kg N ha⁻¹, respectively. Coating urea with 0.2g neem cake per g urea had no effect on loss of urea-N in either year; however, it significantly increased grain yield (0.4 Mg ha⁻¹) and total plant N (11 kg ha⁻¹) in 1987 but not in 1986.     

Integrated Nutrient Management Improves Productivity and Quality of Sugarcane (<i>Saccharum Officinarum</i> L.)

Sugarcane is one of the major important sugar yielding crops in Bangladesh. As an exhaustive crop, sugarcane removes a huge amount of plant nutrients from the soil. However, the combined use of organic and inorganic fertilizers can be a good approach to deal with nutrient depletion and promote sustainable crop production as well as improve soil health. Therefore, an attempt was made to identify the most fruitful and profitable integrated nutrient management on the aspects of growth, yield and quality of sugarcane in two consecutive growing seasons. Seven treatments: T₁=Control, T₂=165:55:120:30:10:2.5:4 kg N:P:K:S:Mg:Zn:B ha⁻¹, T₃=Poultry Litter (PL) at 5 t ha⁻¹+95:51:87:9:10:2.5:4 kg N:P:K:S:Mg:Zn:B ha⁻¹, T₄=Cow Dung (CD) at 15 t ha⁻¹+ 36:52:60:17:10:2.5:4 kg N:P:K:S:Mg:Zn:B ha⁻¹, T₅=Press Mud (PM) at 15 t ha⁻¹+10:50:43:0:10:2.5:4 kg N:P:K:S:Mg:Zn:B ha⁻¹, T₆=Mustard Oil Cake (MOC) at 0.5 t ha⁻¹+140:54:115:25:10:2.5:4 kg N:P:K:S:Mg:Zn:B ha⁻¹ and T₇=GM (Green Manure) at 5 t ha⁻¹+140:53:100:28:10:2.5:4 kg N:P:K:S:Mg:Zn:B ha⁻¹ were used in this experiment. Two years data showed that treatment T₃ produced the maximum amount of tillers, total dry matter yield, millable sugarcane, cane yield and sugar yield, followed by the T₄ treatment. The highest stalk heights were recorded in the T₃ treatment, which was statistically similar to all other treatments except T₁ and T₂. The juice quality parameters viz., brix and pol in cane were found significant in treatment T₃ while the highest purity was obtained in the T₇ treatment. All the data of Jaggery (goor) quality parameters, the highest sucrose content, color transmittance, Jaggery (goor) recovery and the lowest ash content of Jaggery (goor) were observed in the T₃ treatment, which was statistically similar to the T₄ treatment in both seasons. The highest cost of production was obtained from the T₆ treatment while the highest gross return, net return and BCR were recorded in the T₃ treatment. No significant changes were found in one cycle of sugarcane in initial and post-harvest soil characteristics viz., pH, organic carbon, total N, and available P, K and S contents due to integrated use of different fertilizer packages. From the experimental findings, it was concluded that treatment T₃ followed by T₄ treatment would be the better productive and profitable integrated nutrient management technology for ensuring higher yields and quality of sugarcane without soil fertility degradation in the High Ganges River Floodplain soils.     

Nitrogen uptake and recovery from urea and green manure in lowland rice measured by15N and non-isotope techniques

In the recent past considerable attention is paid to minimize dependence on purchased inputs such as inorganic nitrogen fertilizer. Green manure in the form of flood-tolerant, stem-nodulatingSesbania rostrata andAeschynomene afraspera is an alternative N source for rice, which may also increase N use efficiency. Therefore research was conducted to determine the fate of N applied to lowland rice (Oryza sativa L.) in the form ofSesbania rostrata andAeschynomene afraspera green manure and urea in two field experiments using¹⁵N labeled materials.¹⁵N in the soil and rice plant was determined, and¹⁵N balances established. Apparent N recoveries were determined by non-tracer method. ¹⁵N recoveries averaged 90 and 65% of N applied for green manure and urea treatments, respectively. High partial pressures of NH₃ in the floodwater, and high pH probably resulted from urea application and favoured losses of N from the urea treatment. Results show that green manure N can supply a substantial proportion of the N requirements of lowland rice. Nitrogen released fromSesbania rostrata andAeschynomene afraspera green manure was in synchrony with the demand of the rice plant. The effect of combined application of green manure and urea on N losses from urea fertilizer were also investigated. Green manure reduced the N losses from¹⁵N labeled urea possibly due to a reduction in pH of the floodwater. Positive added N interactions (ANIs) were observed. At harvest, an average of 45 and 25% of N applied remained in the soil for green manure and urea, respectively.Contribution from IRRI, Los Baños, Philippines and Justus-Liebig-University, Giessen, GermanyContribution from IRRI, Los Baños, Philippines and Justus-Liebig-University, Giessen, Germany     

The fate of spring applied fertilizer N during the autumn-winter period: comparison between winter-fallow and green manure cropped soil

A field experiment was carried out at a pilot plot that was cropped with oilseed rape, and then left partly fallow and partly cropped with a green manure (mustard) during the autumn after harvest of the oilseed rape. The rape residues were incorporated in the soil. Methods used to quantify the N fluxes from harvest until sowing of the next crop were (1) ¹⁵N balance method, (2) total mineral N analysis and (3) NO emission measurements. Losses of spring applied fertilizer N were negligible in cropped plots and minimal in fallow plots during the following autumn-winter period. Most of the plant-N residues was retained by the organic N pool of the upper 30-cm soil layer. The green manure contributed slightly to soil available N at sowing of the next crop. However, the incorporation of plant material resulted in a nitrate flux that was at risk of leaching on the fallow plots, and on the green manure plots after incorporation of the green manure. This nitrate was largely derived from soil organic N, not from unused fertilizer applied in spring or from immobilized fertilizer. The NO emissions from the green manure plots were significantly higher than emissions from the fallow plots. The plants had a stimulating effect on the NO emission. A relationship between the NO emission and the soil nitrate concentration could not be established. No emissions were measured after green manure incorporation due to the low temperatures at the pilot plot. However, a greenhouse experiment showed an increased emission after incorporation. The NO emissions seemed to be related with the soil ammonium concentration.     

Impacts of Agricultural Management and Climate Change on Future Soil Organic Carbon Dynamics in North China Plain

Dynamics of cropland soil organic carbon (SOC) in response to different management practices and environmental conditions across North China Plain (NCP) were studied using a modeling approach. We identified the key variables driving SOC changes at a high spatial resolution (10 km×10 km) and long time scale (90 years). The model used future climatic data from the FGOALS model based on four future greenhouse gas (GHG) concentration scenarios. Agricultural practices included different rates of nitrogen (N) fertilization, manure application, and stubble retention. We found that SOC change was significantly influenced by the management practices of stubble retention (linearly positive), manure application (linearly positive) and nitrogen fertilization (nonlinearly positive) – and the edaphic variable of initial SOC content (linearly negative). Temperature had weakly positive effects, while precipitation had negligible impacts on SOC dynamics under current irrigation management. The effects of increased N fertilization on SOC changes were most significant between the rates of 0 and 300 kg ha⁻¹ yr⁻¹. With a moderate rate of manure application (i.e., 2000 kg ha⁻¹ yr⁻¹), stubble retention (i.e., 50%), and an optimal rate of nitrogen fertilization (i.e., 300 kg ha⁻¹ yr⁻¹), more than 60% of the study area showed an increase in SOC, and the average SOC density across NCP was relatively steady during the study period. If the rates of manure application and stubble retention doubled (i.e., manure application rate of 4000 kg ha⁻¹ yr⁻¹ and stubble retention rate of 100%), soils across more than 90% of the study area would act as a net C sink, and the average SOC density kept increasing from 40 Mg ha⁻¹ during 2010s to the current worldwide average of ∼55 Mg ha⁻¹ during 2060s. The results can help target agricultural management practices for effectively mitigating climate change through soil C sequestration.     

Assessment of Nutrient Leaching Losses and Crop Uptake with Organic Fertilization,Water Saving Practices and Reduced Inorganic Fertilizer

The increasing world population has forced excessive chemical fertilizer and irrigation to complete the global food demand, deteriorating the water quality and nutrient losses. Short-term studies do not compile the evidences; therefore, the study aimed to identify the effectiveness of reduced doses of inorganic fertilizer and water-saving practices, hence, a six-year experiment (2015–2020) was conducted in China to address the knowledge gap. The experimental treatments were: farmer accustomed fertilization used as control (525:180:30 kg NPK ha⁻¹), fertilizer decrement (450:150:15 kg NPK ha⁻¹), fertilizer decrement + water-saving irrigation (450:150:15 kg NPK ha⁻¹), application of organic and inorganic fertilizer + water-saving irrigation (375:120:0 kg NPK ha⁻¹ + 4.5 tones organic fertilizer ha⁻¹), and application of controlled-release fertilizer (80:120:15 kg NPK ha⁻¹). Each treatment was replicated thrice following a randomized complete block design. The results achieved herein showed that control has the highest losses in the six-year study for total nitrogen (225.97 mg L⁻¹), total soluble nitrogen (121.58 mg L⁻¹), nitrate nitrogen (0.93 mg L⁻¹), total phosphorus (0.57 mg L⁻¹), and total soluble phosphorus (0.57 mg L⁻¹) respectively. Reduced fertilizer and water application improved crop nutrient uptake, nitrogen concentration was significantly enhanced with organic and inorganic fertilizer + water-saving irrigation, P concentration was increased with fertilizer decrement + water-saving irrigation, and K concentration was improved with fertilizer decrement + water-saving irrigation. Hence, this study concludes that reduced inorganic fertilizer dose combined with water-saving practices is significantly helpful in reducing nutrient leaching losses and improving nutrient uptake and water pollution. Further studies are needed to explore the impacts of reduced fertilization and water-saving irrigation on leaching losses. The benefits at different climatic conditions, soil types, and fertilizer types with application methods are also a research gap.

     

Soil property,CO2 emission and aridity index as agroecological indicators to assess the mineralization of cover crop green manure in a Mediterranean environment

In this study soil chemical and biochemical properties, cover crop biomass production and quality, and climatic factors (AI) have been taken into account in order to identify sensitive agroecological indicators suitable for an early assessment of green manuring outcomes, measured in terms of soil CO₂ emission and soil mineralization dynamics in a short term experiment in a Mediterranean environment. The field experiment was conducted over two cropping rotations during 2004–2005 in central Italy. A winter cover crop/sweet pepper sequence with the cover crop used as green manure was adopted. The cover crop treatments were common vetch (CV), rye grass (RG), and fallow soil as the control (Control). Soil enzyme activities (acid phosphatase. protease and β-glucosidase), CO₂ emission, and inorganic nitrogen concentrations were monitored from cover crop green manure incorporation to pepper harvesting in order to evaluate soil mineralization dynamics. The climatic conditions were summarized by the monthly aridity index (AI) calculated as the precipitation/temperature ratio. A group of mineralization indexes, calculated using values of available nitrogen and enzyme activities, was used to describe the soil process during crop cycle after green manure. The mineralization process dynamic results as a combined effect of climatic conditions and soil organic matter quality produced by different cover crop green manures. The common vetch green manuring was effective in lowering the soil C/N with respect to the control soil (5.7 vs. 8.3 and 8.5 vs. 12.1 in 2004 and 2005, respectively), promoting CO₂ emission (8.95 vs. 5.19 and 6.75 vs. 4.28 Mg CO₂-C ha⁻¹ in 2004 and 2005, respectively), enzyme activity, nitrogen release, and crop aboveground biomass (8.59 vs. 7.05 Mg ha⁻¹ dry matter). Among the selected agroecological indicators, the relationships between enzyme activities and the monthly aridity index may suggest a new approach for agronomists and soil scientists to understand the combined effect of temperature and precipitation on soil mineralization dynamic. The high aridity index at the time of green manuring may have caused a priming effect of SOM and promoted soil mineralization during the vegetable crop growing season in a Mediterranean environment. Finally, no evidence was found between soil CO₂ emission and the aridity index; soil respiration was mainly affected by cover crop biomass and the soil C/N ratio.