Nitrogen Fertilizer Application Rates Research Articles

Digital image processing technology under backpropagation neural network and K-Means Clustering algorithm on nitrogen utilization rate of Chinese cabbages.

The purposes are to monitor the nitrogen utilization efficiency of crops and intelligently evaluate the absorption of nutrients by crops during the production process. The research object is Chinese cabbage. The Chinese cabbage population with different agricultural parameters is constructed through different densities and nitrogen fertilizer application rates based on digital image processing technology, and an estimation NC (Nitrogen Content) model is established. The population is classified through the K-Means Clustering algorithm using the feature extraction method, and the Chinese cabbage population quality BPNN (Backpropagation Neural Network) model is constructed. The nonlinear mapping relationship between different agricultural parameters and population quality, and the contribution rate of each indicator, are studied. The nitrogen utilization of Chinese cabbage is monitored effectively. Results demonstrate that the proposed NC estimation model has correlation coefficients above 0.70 in different growth stages. This model can accurately estimate the NC of the Chinese cabbage population. The results of the Chinese cabbage population quality BPNN model show that the population planting density based on the seedling number is reasonable. The constructed population quality evaluation model has a high R2 value and a comparatively low RMSE (Root Mean Square Error) value for the quality evaluation of Chinese cabbage in different periods, showing that it applies to evaluate the population quality of Chinese cabbage in different growth stages. The constructed nitrogen utilization model and quality evaluation model can monitor the nutrient utilization of crops in different growth stages, ascertain the agricultural characteristics of other yield groups in different growth stages, and clarify the performance of agricultural parameters in different growth stages. The above results can provide some ideas for crop growth intelligent detection.

The Change in Winter Wheat Response to Deoxynivalenol and Fusarium Head Blight Through Technological and Agronomic Progress

Fusarium head blight (FHB) in wheat causes yield loss, quality reduction, and mycotoxin contamination in temperate wheat production areas worldwide. The objective of this study was to quantify the progress of agronomic and FHB management strategies over the past two decades in FHB suppression and agronomic performance of winter wheat in environments favorable for FHB. Field experiments were conducted in environments typical of FHB epidemics to compare common agronomic and FHB management practices used in the 1996 era compared with those used in 2016. The experiments included a comparison of three different nitrogen (N) fertilizer application rates and six old (1996-era) and new (modern-era) winter wheat cultivars representing combinations of susceptibility and era to FHB, with and without a fungicide applied at flowering (pydiflumetofen + propiconazole). To mimic environments favorable for infection (similar to 1996 in Ontario, Canada), plots were challenged at 50% anthesis with F. graminearum macroconidia suspension followed by mist irrigation. The modern management strategy of using moderately resistant cultivars, a fungicide applied at flowering, and a high rate of N fertilizer reduced total deoxynivalenol by 67%, reduced Fusarium-damaged kernels by 49%, reduced FHB index by 86%, increased grain test weight by 11%, and increased grain yield by 31% compared with the standard management practice of seeding highly susceptible cultivars with no fungicide and a lower rate of N fertilizer recommended in the 1996 era. This study enabled a published economic assessment of the return on investment for the improvements in cultivars, fungicide, and N fertilizer applications since 1996.

Influence of nitrogen and mineral fertilizer application rates for legumes on the number of stems and the amount of NPK in the soil

Inoculation of seeds of legumes (soybean - Glycine max L., mung bean - Phaseolus aureus L., wild beans - Phaseolus) grown as a secondary crop after winter wheat before sowing with nitragin and application of mineral fertilizers in different doses affected the amount of endogenous bacteria formed in the plant root as well as the agrochemical properties of the soil. Inoculation of legume seeds with nitragin before sowing and application of mineral fertilizers at different rates increased the amount of humus in the topsoil (0-30 cm) layer by 0.025-0.029% compared to the initial values, and the total nitrogen content by 0.009-0.012%. The formation of endogenous bacteria in the root of the plant was inoculated with nitrogen before sowing the seeds of soybean, moss, bean crops. The amount of legumes was 22.7-36.7 pieces in the variant, in which the mineral fertilizers N30 R90 K60 kg/ha was applied, whereas it was 12.0-15.6 pieces in the variant without any mineral fertilizers.

A hybrid decision tool for optimizing broccoli production in a changing climate

Climatic changes are already influencing the frequency, magnitude, and duration of extreme weathers (e.g. drought) in California. California is a leading state for vegetable production in United States (U.S.). Since vegetables are very sensitive to extreme weathers, it is critical to evaluate the effects of climate change on yield and to find the potential adaptive management strategies for the sustainable vegetable production. The objectives of this study were to develop a plant-oriented cropping model to evaluate the impacts of different cropping managements on yields under various climate condition and atmospheric CO2 levels. To improve modeling performance, numerous previous studies that reported broccoli yields in different managements were used. After model calibration and validation, 560 scenarios under the conditions of combinations of climate changes, four broccoli cultivars, five nitrogen fertilizer application rates, and four plant densities were simulated in two study locations in Monterey County, CA where produces almost 40% of total California broccoli production. Based on results from 33,600 simulations, broccoli yields were highly related to nitrogen fertilizer application. However, at high nitrogen rates (above 75 kg N ha−1), yields were barely changed. In general, under stressful conditions, all cultivars produced their maximum yields at low plant density, and their yields did not respond to addition of nutrient in soil. However, CO2 enrichment and warmer temperature under RCP8.5 pathways, yield responded positively with fertilizer application rate and plant density. It seems likely that the effects of cropping managements will depend upon CO2 level and temperature.

115 Nitrogen fertilizer effects on above ground sward characteristics and beef heifer performance from native warm-season grass blends

Abstract A 2-yr study was conducted at Black Belt Research and Extension Center in Marion Junction, AL, to evaluate the effect of nitrogen (N) fertilizer application rate on forage production characteristics, nutritive value, and animal performance of beef heifers grazing a mixture of native warm-season grasses (NWSG) including big bluestem, little bluestem, and indiangrass. Six, two-hectare plots were randomly assigned to one of two treatments (0 or 67 kg N ha-1 applied in early April; n = 3 replications per treatment). Paddocks were continuously stocked with four weaned Angus × Simmental beef heifers (initial BW 288 ± 7 kg) from late May/early June through mid-to-late August during 2018 (73 grazing d) and 2019 (70 grazing d), respectively. Put-and-take cattle were used to manage forage to a target of 38 cm. Forage mass and canopy heights were collected every two weeks during the trial. Visual ground cover ratings, canopy light interception, and botanical composition were measured at the beginning and end of the trial in each year. Hand-plucked samples were collected every two weeks during the grazing trial to determine forage nutritional value. Data were analyzed using the PROC MIXED procedure in SAS 9.4, and differences were declared significant when P ≤ 0.05. Nitrogen fertilized NWSG had greater crude protein (P < 0.0001), sward heights (P = 0.0003), and canopy light interception at the beginning of the season (P = 0.0049) compared to non-fertilized paddocks. However, there were no differences (P ≥ 0.05) among N-fertility treatments for mean forage mass, heifer ADG, or BCS across the 2-yr study. Botanical composition data indicated that indiangrass decreased from 64% to 61% (P = 0.0022) and weed pressure increased from 11% to 15% (P = 0.0064) across the summer grazing season. Canopy light interception decreased by 51% from early June to August in fertilized NWSG and 26% in unfertilized paddocks, respectively. These data illustrate that NWSG systems may provide a viable grazing system in the summer months under reduced N inputs.

Ridge-furrow configuration significantly improves soil water availability, crop water use efficiency, and grain yield in dryland agroecosystems of the Loess Plateau

The ridge-furrow rainfall harvesting system (RFRHS) is an in-situ rainfall collection and utilization technique that has been widely adopted in global arid and semiarid farming areas because of its significant benefits to soil water availability and crop yield. However, the integrated effects of different ridge-furrow configurations on rainwater collection and crop performance are still lacking. Using a specialized database drawn from field experiments in the Loess Plateau, we examined the regional effects of three typical ridge-furrow configurations, namely high (>1:1), uniform (=1:1), and low (<1:1) ridge-furrow ratios, on soil water storage, crop water use efficiency (WUE), and grain yield. The high ridge-furrow ratio achieved the greatest improvements in soil water storage than the other two ratios. Compared with traditional flat planting without ridge-furrow configuration, crop yield and WUE were significantly increased by 37.65%, 27.12%, 31.70%, and 47.70%, 30.00%, and 17.80% under high, uniform, and low ridge-furrow ratios, respectively. Improvements in crop yield and WUE due to the different ridge-furrow configurations were jointly affected by climate, soil organic matter, and fertilizer application. The mean annual precipitation of 600 mm and the mean annual temperature of 12 ℃ can be used as the threshold for selecting the ratio of ridge–furrow. An increase in soil organic matter gradually declined the increase in grain yield and WUE owing to the three ridge–furrow ratios, such that the maximum effect was found for the high ridge–furrow ratio. Among the three ratios, the improvements in crop yield and WUE were most notable when the application rates of nitrogen and phosphorus fertilizer were 100–200 kg ha−1 and 101–125 kg ha−1, respectively. This study examined the scientific basis of a ridge–furrow farming practice for enhancing rainfall use and crop WUE; thus, these results offer novel insights for the optimized design of a ridge–furrow ratio in dryland agroecosystems of the Loess Plateau by taking into account site-based climatic conditions, soil fertility, and fertilization input level.

Carbon footprint of a typical pomelo production region in China based on farm survey data

Greenhouse gas emissions are a central environmental concern in China, and quantifying the carbon footprint of crop production can help identify key options for mitigating greenhouse gas emissions from agriculture. Using two-year farm survey data from a typical pomelo production area in China, the carbon footprint of a pomelo orchard was assessed by quantifying the greenhouse gas emissions from farming inputs and operations with a full life cycle assessment methodology. The carbon emission and carbon sequestration levels were 19.9 and 3.43 t CO2 eq ha−1, respectively. The farm carbon footprint and product carbon footprint were 16.5 t CO2 eq ha−1 and 0.33 t CO2 eq t−1, respectively, which were 3.8 and 1.5 times greater than the corresponding mean values for other fruit orchards in different areas of the world. Compared with farms with low yield and high carbon footprint, farms with high yield and low carbon footprint reduced nitrogen fertilizer input significantly, by 44.7%. Furthermore, the yield of farms which with high yield and low carbon footprint increased significantly by 69.4%, and the farm carbon footprint and product carbon footprint significantly decreased by 40.7% and 67.2%, respectively, compared to those of farms with low yield and high carbon footprint. The synthetic nitrogen fertilizer application rate was significantly linearly correlated with, and contributed 84.7% to the carbon footprint of pomelo production. The relationships between the carbon footprint and the nitrogen partial factor productivity also indicated that improving nitrogen utilization can effectively reduce greenhouse gas emissions. In addition, based on group analysis, the difference in carbon footprint among farm groups was also mainly due to nitrogen fertilization. Reducing costs can significantly improve carbon efficiency without affecting the economic benefit at similar yield levels. Therefore, the carbon intensity of pomelo production in China could be reduced primarily by reducing excessive nitrogen fertilizer application and potentially increasing nitrogen use efficiency. Apart from this, these differences could be implemented by modifying farming fertilization strategies and farm size. Overall, this study highlights the importance of strengthening nitrogen management in pomelo production based on agricultural practices as well as upscaling farm size, which could achieve higher yields with lower greenhouse gas emissions and thereby avoid tradeoffs between productivity and carbon costs.

English

A field experiment was conducted at the Teaching and Research Farm of the Adamawa State College of Agriculture at Mubi, Nigeria to determine effect of Nitrogen fertilization on the growth and yield of Finger Millet (Eleusine coracana L. (Garten). Results indicated that all the growth and yield components were significantly (p &le; 0.05) influenced by increasing nitrogen fertilizer application rates. The highest performances for all the parameters were recorded at the application rate of 600 kg Nha-1. Growth and yield components were found to be positive and linearly related to increasing nitrogen rates. It is therefore recommended that Finger millet be fertilized with 600 kg Nha-1, at Mubi. &nbsp; Key words: Finger millet, nitrogen fertilization, savanna ecological zone, nutritious, semi-arid.

The response of flue-cured tobacco cultivar K326 to nitrogen fertilizer rate in China

AbstractNitrogen is an important element for the growth of flue-cured tobacco and is closely related to its yield and quality. In order to pursue higher economic benefits, excessive fertilizer is generally applied in flue-cured tobacco production, which is unfavourable for the sustainable development of flue-cured tobacco production and for the environment. In 2016 and 2017, experiments using different nitrogen fertilizer application rates in flue-cure tobacco were conducted in Yunnan province, and the changes in agronomic, economic and chemical indices as well as in residual soil nitrogen were compared. Linear and quadratic models were used to compare the response of tobacco to nitrogen fertilizer. With increasing nitrogen fertilizer rate, the proportions of superior to medium tobacco and the average price of flue-cured tobacco leaves initially increased and then decreased, while fresh weight, dry weight and the proportion of inferior tobacco showed the opposite trend. Total sugar and reducing sugar contents decreased with increasing nitrogen fertilizer rates, while total nitrogen and nicotine contents increased. Sensory evaluation scores had the highest value when 90 kg N/ha and 120 kg N/ha were applied. Soil nitrate contents increased as nitrogen fertilizer rate increased. The quadratic model was suitable for the response of cultivar K326 to nitrogen and 90 kg N/ha could meet the needs of cultivar K326.

Effects of Nitrogen and Phosphorus Fertilizer Rates on Maize (Zea mays L.) Growth and Yields in Terraced Lands of Medium and High Altitude Regions of Rwanda

Depletion of nitrogen and phosphorus in terraced hilly areas of Rwanda has lowered maize (Zea mays L.) production. Trials were carried out in 2017 and 2018 in four-year-old-terraced Lixisols and Acrisols of medium and high altitudes to determine effect of nitrogen and phosphorus fertilizer application rates on maize yields. A factorial arrangement of four levels of nitrogen (0, 60, 120 and 180 kg N ha-1) and phosphorus (0, 40, 80 and 120 kg P2O5 ha-1) in a randomized complete block design with 3 replications, was used. Results showed that combinations of 120 - 180 kg N ha-1 and 80 - 120 kg P2O5 ha-1 resulted in significantly (P less than 0.05) higher increases in plant height (45 – 60 % and 56 – 70 % over the control), stem collar diameter (63 – 74 % and 43 % over the control) and grain yields (3 times over the control; i.e. 6.40 – 6.46 t ha-1 and 6.02 - 6.12 t ha-1) in medium and high altitude sites. The optimum fertilizer rates are 176.6 kg N ha-1 and 96.2 kg P2O5 ha-1 in terraced Lixisols of medium altitude area. Land use needs to adjust fertilizer application to these optimum rates for enhanced maize yields in this area and other regions with similar agro-ecological characteristics. Further studies on integrated effects of N and P fertilizers are recommended.

Impacts of nitrogen fertilizer type and application rate on soil acidification rate under a wheat-maize double cropping system

Nitrogen (N) fertilizer-induced soil acidification in Chinese croplands is well-known, but insight in the impacts of different N fertilizer management approaches (fertilizer type and rate) on soil acidification rates is very limited. Here, we conducted a field experiment on a moderate acid soil to quantify soil acidification rates in response to N fertilization by different fertilizer types and N rates through monitoring the fate of elements (mainly nutrients) related to H+ production and consumption. Two N fertilizer types (urea and NH4Cl) and three N rates (control, optimized and conventional, 0/120/240 kg N ha−1 for wheat, 0/160/320 kg N ha−1 for maize) were included. Nitrogen addition led to an average H+ production of 4.0, 8.7, 11.4, 29.7 and 52.6 keq ha−1 yr−1, respectively, for the control, optimized urea, conventional urea, optimized NH4Cl and conventional NH4Cl plots. This was accompanied with a decline in soil base saturation of 1–10% and in soil pH of 0.1–0.7 units in the topsoil (0–20 cm). Removal of base cations by crop harvesting and N transformations contributed ~70% and ~20% to the H+ production in the urea treated plots, being ~20% and ~75% in the NH4Cl treated plots, respectively. The large NH4+ input via fertilization in the NH4Cl treated plots strongly enhanced the H+ production induced by N transformations. The low contribution of N transformations to the H+ production in the urea treated plots was due to the limited NO3− leaching, induced by the high N losses to air caused by denitrification. Increased N addition by urea, however, strongly increased H+ production by enhanced plant uptake of base cations, mainly due to a large potassium uptake in straw. Our results highlight the important role of optimizing fertilizer form and N rate as well as straw return to the field in alleviating soil acidification.

Response of the arbuscular mycorrhizal fungi diversity and community in maize and soybean rhizosphere soil and roots to intercropping systems with different nitrogen application rates

Maize (Zea mays L.)/soybean (Glycine max L.) intercropping has been widely practiced in China, because of its effectiveness in improving crop yield and nitrogen utilization efficiency. However, the responses of indigenous arbuscular mycorrhizal fungal (AMF) diversity and communities in rhizosphere soil and roots to intercropping systems with different nitrogen application rates remain unclear. In this study, a field experiment was conducted with split-plot design, and AMF communities in crop rhizosphere soil and roots in monoculture and intercropping systems treated with different levels of nitrogen fertilization were investigated using Illumina MiSeq sequencing. Nitrogen fertilization significantly decreased the AMF alpha-diversity in maize rhizosphere soil, and no significant differences were observed between monocultured and intercropped maize. The Shannon index of soybean rhizosphere soil was significantly higher in intercropping treatments than in monoculture treatments for the corresponding nitrogen levels. The AMF diversity in the roots of maize showed different trends to those in the soil. The dominant genera in the present study were Glomus_f_Glomeraceae, Paraglomus, and Gigaspora, which occupied 55.52%, 9.18%, and 8.20% of the rhizosphere soil and 65.35%, 5.32%, and 17.16% of the roots, respectively. Our study showed that the abundance of the dominant genus, Glomus_f_Glomeraceae in maize soil and roots significantly increased in intercropping treatments compared with monoculture treatments, and it also increased with the increase in nitrogen application levels. In soybean soil and roots, the abundance of Glomus_f_Glomeraceae decreased with the increase in nitrogen application levels. The results of the redundancy and correlations analyses indicated that the changes in the AMF diversity and community in intercropping areas were significantly associated with alterations of the soil total nitrogen and alkali-hydrolysable nitrogen due to the interactions between maize and soybeans in intercropping systems with different nitrogen fertilizer application rates.

Timing and rate of nitrogen fertilization influence maize yield and nitrogen use efficiency.

Timing and rate of nitrogen (N) fertilizer application can influence maize (Zea mays L.) grain yield, N uptake, and nitrogen use efficiency (NUE) parameters, but results have been inconsistent across the upper Midwest. This study compared single (fall and preplant) and split applications of differing N rates for maize under irrigated conditions on loamy sand at Becker, MN and under rainfed conditions on loam and clay loam soils at Lamberton, MN and Waseca, MN, respectively, in 2014 to 2016. Fall and preplant applications of N were applied at recommended and 125% of recommended rates (RN) according to University of Minnesota guidelines. Split-application treatments included a two-way (Sp, applied at 75% and 100% of RN) and a three-way split (TSp applied at 50%, 75%, and 100% of RN), with the total N rate equally split among application times. At Becker, maize grain yield with TSp was 12.6 to 15.7 Mg ha-1 among years and significantly greater than that with fall or preplant treatments. The TSp treatment also improved agronomic efficiency (AE) and recovery efficiency (RE) by an average of 30% over fall or preplant treatments. At Lamberton, maize grain yield, AE and RE did not differ among treatments. However, TSp75 improved AE by 8.3 kg kg-1 while producing comparable yields to fall and preplant treatments. At Waseca, Sp or TSp improved grain yield and AE compared with fall treatments. These results suggest that split applications of N can increase maize grain yield, AE, and RE on irrigated coarse-textured soils and applying N fertilizer near planting or as a split application can improve N management on non-irrigated clay loam soils.

Response of Cowpea (Vigna unguiculata L. Walp) to Time of Application and Nitrogen Fertilizer on the Degraded Soil of Southern Guinea Savanna Zone of Nigeria

Field trials were conducted during 2017 and 2018 rainy season, to investigate the effect of nitrogen fertilizer rates and time of application on the growth and yield of cowpea. The treatment consisted of three levels of urea: 0, 40, 80 kg N ha-1 and the times of fertilizer application: during planting of cowpea, 2 weeks after planting, 4 weeks after planting and 6 weeks after planting; which were factorially combined to form twelve treatments and laid in Randomized Complete Block Design (RCBD). The results showed that, Nitrogen fertilizer rates and time of application had a significant increased on all the growth and yield parameters of cowpea in both years of trials. Application of 80 kg N ha-1 produced the highest number of cowpea leaves (134.45 and 139.23), number of branches (9.45 and 10.54), vine length (78.23cm and 80.12cm) and highest seed weight of 0.52 t ha-1 in both 2017 and 2018 trials. However, the control plots produced plants with the highest number of root nodules (14.78 and 12.49) in both years of cropping. Also, application of nitrogen fertilizer at two weeks after planting of cowpea produced the highest growth and seed weight of 0.68 t ha-1 in 2017 cropping; while in 2018 trial, application of nitrogen fertilizer at two weeks after cowpea planting produced seed yield of 0.69tha-1 which is statistically similar with application of nitrogen fertilizer on the fourth week after planting which produced 0.55 t ha-1 of cowpea seeds. The interaction between nitrogen fertilizer application rates and time of application did not showed any significant difference in cowpea yield and yield components in both years of cropping.

Comparison of different approaches for optimizing nitrogen management in sprinkler-irrigated maize

• Optimized fertilization strategies can reduce up to 236 kg N ha −1 compared to actual practices. • Using field-specific information decreased recommended N rates compared to a fixed reduced N rate. • The use of a portable chlorophyll meter device (SPAD) increase NUE in most field situations. The gap between scientifically sound nitrogen (N) fertilizer application rates and the actual rates used by farmers in maize is still significant. The improvement of nitrogen use efficiency in such a highly N-demanding crop is necessary to decrease the negative effects of N fertilization. The objective was to compare the performance of different N management treatments in maize grown under semiarid Mediterranean sprinkler-irrigated conditions to the standard farmer practice. We compared an agronomically sound fixed rate of N fertilizer (FR) with a variable N rate obtained based on a soil mineral balance at pre-planting (SB) or based on a portable chlorophyll meter readings (CM) made just before tasseling. Additional treatments were a N control, without fertilizer (T0), and a non-limiting N (NL) treatment wich was typical of the current farmer practice. The study was replicated at 5 sites in one-year experiments and under 3 pre-planting soil mineral nitrogen environments (SMN, Low, Medium, and High). The results demonstrate the potential to reduce N rates from zero to 236 kg N ha −1 compared to the NL in irrigated maize fields without compromising yields in most of the situations with a subsequent increase of NUE. Averaging over sites, the use of fine-tuning N fertilizer strategies that considered field-specific conditions (SB and CM) reduced N rates (38 %) compared to the reductions under the FR strategy (26 %) relative to the NL conditions, which is the treatment closest to a typical farmer`s application rate.

Farm-scale carbon and nitrogen fluxes in pastoral dairy production systems using different nitrogen fertilizer regimes

The nitrogen (N) fertilizer application rate (kg ha−1 year−1) in pastoral dairy systems affects the flow of N through the soil, plant and animal pools of the system. With better understanding of the magnitude of these pools and their fluxes, dairy systems could be managed to improve N use efficiency, therefore reducing losses to the environment. A study with three levels of N fertilizer, 0 (N0), 150 (N150) and 300 (N300) kg N ha−1 year−1, was conducted in the Canterbury region of New Zealand from 1 June 2017 till 31 May 2018. Farm measurements, e.g. pasture and milk production, were used to calibrate three different farm-scale models, DairyNZ’s Whole Farm Model, DairyMod, and Overseer®. The models were used to extrapolate periodic farm measurements to predictions of carbon (C) and N pools and fluxes on an annual basis. Pasture and milk production per hectare increased from N0 to N300 by 70 and 58%, respectively. There was a concomitant increase in farm-gate N surplus (input–output) of 43%, resulting in predicted increases in N leaching and greenhouse gas emissions of 72 and 67%, respectively. By increasing N fertilizer from 0 to 300 kg N ha−1 year−1, 53% more feed N flowed through the dairy herd with surplus N deposited as urinary N increasing by 49%. Plant uptake and soil immobilization increased by 58 and 343%, respectively, but not enough to avoid substantial increases in leaching and emission losses. Carbon flux through the soil system increased through increased litter and faecal deposition, but with very little C sequestration because of accelerated microbial respiration rates.

Effect of Organic Fertilizer and Inorganic Fertilizer Application on N2O Emissions from Fluvo-aquic Soil in the North China Plain

The North China Plain is an important grain production area in China. Due to the low content of soil organic carbon, increasing the application rate of nitrogen fertilizer would not lead to a continuous increase of maize yield at present. The combined application of organic fertilizer and inorganic fertilizer is widely regarded as a measure to simultaneously increase grain yield and soil organic carbon; however, the effect of organic fertilizer and inorganic fertilizer application on N2O emissions from farmland in the North China Plain is unclear. Here, N2O emissions and crop yields in cropland under the combined application of different types and rates of organic fertilizers plus inorganic N fertilizer were measured in the North China Plain. The field experiment included eight treatments:no N fertilizer (CK), inorganic fertilizer (NPK), 40% cow manure N plus 60% inorganic fertilizer N (CM), 40% chicken manure N plus 60% inorganic fertilizer N (FC), 40% pig manure N plus 60% inorganic fertilizer N (FP), 20% cow manure N plus 80% inorganic fertilizer N (1/2CM), 20% chicken manure N plus 80% inorganic fertilizer N (1/2FC), and 20% pig manure N plus 80% inorganic fertilizer N (1/2FP). The N2O fluxes were significantly correlated with soil water-filled pore space during the maize season (P<0.05). There was a significant linear relationship between N2O fluxes and soil dissolved organic carbon content during the maize season in all treatments except the NPK treatment. In the maize season, N2O emission was 0.50 kg·hm-2 under CK treatment, and increased to 2.28 kg·hm-2 under NPK treatment. However, when the proportion of manure N to total N applied was reduced from 40% to 20%, N2O emissions were significantly reduced by 33.6%, 43.7%, and 12.1% under 1/2CM, 1/2FC, and 1/2FP treatments, respectively. The difference in application rate of organic manure N did not significantly affect maize yield. The reduction of N2O emission at the low manure application rate compared with the high manure application rate was likely due to the decrease in dissolved organic carbon in soils.

Carbon limits non-linear response of nitrous oxide (N2O) to increasing N inputs in a highly-weathered tropical soil in Sri Lanka

There is growing evidence for a positive non-linear response in N2O emissions where increasing N fertilizer rates critically exceed crop requirements from a range of cropping systems. However, the majority of these studies have been conducted in temperate regions, and it remains unclear if the non-linear response hypothesis can be transferred to tropical regions due to their inherently lower carbon (C) content and fertility. This study assessed the impact of different nitrogen (N) fertilizer application rates in combination with a carbon source (green-waste compost) on soil nitrous oxide (N2O) and carbon dioxide (CO2) emissions and crop productivity from a maize-soybean rotation in tropical Sri Lanka. Low cation exchange capacity and extremely high rainfall promoted higher annual cumulative N2O emissions than reported from other cropping systems, ranging from 2.4–9.16 kg N2O-N ha−1 yr−1 for the different fertilizer rates (0 N, 100 N, 220 N, 300 N). The ΔN2O emitted for every additional kilogram of fertilizer N applied (i.e. the marginal N2O emission), declined from ∼24 g kg−1 for the first 0−100 kg N applied to 7 g kg−1 at 300 kg N. This resulted in declining Emission Factors with increasing N rate, as factors other than N limited denitrification. The addition of compost removed this limitation, resulting in constant ΔN2O production rates and Emission Factors with increasing N inputs, suggesting low C availability limited N2O production at high N rates. The study shows that the non-linear response hypothesis might not hold for highly weathered tropical soils, where C availability limits N2O emissions at high N inputs. While the use of compost can be a viable option to increase soil fertility in these highly weathered tropical soils, it needs to be balanced with reduced N fertilizer application rates to avoid elevated losses of N2O.

Morphological Response of Maize (Zea mays) to Nitrogen Fertilizer Application Rate at SNNP, Ethiopia

Morphological Response of Maize (Zea mays) to Nitrogen Fertilizer Application Rate at SNNP, Ethiopia

Using a Crop Modeling Framework for Precision Cost-Benefit Analysis of Variable Seeding and Nitrogen Application Rates

A key goal of precision agriculture is to achieve the maximum crop yield while minimizing inputs and loses from cropping systems. The challenge of precision agriculture is these factors interact with one another on a subfield scale. The seeding density and the nitrogen (N) fertilizer application rate are two of the most important inputs influencing agronomic, economic and environmental outcomes including yield, return on investment (ROI) and nitrate (NO3-) leaching. A cropping system simulation framework is used to predict site-specific subfield optimum seeding density and (N) fertilizer application rates for the economic optimum (maximum ROI) versus agronomic optimum (maximum yield). The framework couples the process-based APSIM cropping system model with the SSURGO soils database, Daymet weather data service, land grant university estimates of crop production costs and commodity price estimates, and the R statistics software. The framework performance was evaluated using multiple years of precision yield monitor data obtained from a continuous maize (Zea mays L.) cropping system field experiment with varying N-fertilizer rates. Subfield model estimates of crop yield were sensitive to initial conditions related to historical management of the field and had an r2 = 0.65 and a root mean square error of 2356.0 kg ha-1. A site-specific application of the framework comparing economic optimum seeding density and N-fertilizer rates with agronomic optimum values estimated the average ROI benefit to be up to 12.1% with a NO3- leaching reduction of up to 15.2 kg ha-1 at the economic optimum. However, in a minority of cases NO3- leaching was greater at the economic optimum, indicating that managing to maximize ROI rather than yield may not always reduce environmental impacts. Our results suggest that managing cropping systems for the economic optimum is plausible using publicly available data with our framework and may likely lead to improved environmental outcomes.