Dissolved organic nitrogen fluxes and crop yield after long-term crop straw incorporation

The transportation of dissolved organic nitrogen (DON) from croplands to aquatic ecosystems potentially negatively influences water quality. Sustaining crop yields while decreasing the environmental impacts of the DON from nitrogen fertilizer application is a key challenge in sustainable agriculture. However, few field datasets have measured the lateral transportation of DON via hydrological routes under different nitrogen fertilizer applications, particularly in sloping croplands. Using lysimeter plots (8?×?4 m²), we measured DON loss via overland flow, interflow, and soil erosion under different fertilizer applications under a long-term field experiment. There were four treatments, including no fertilizer (CK), mineral fertilizer (NPK), mineral fertilizer combined with swine manure (MNPK), and mineral fertilizer combined with crop straw (CNPK). In comparison to the NPK treatment, the annual DON loss fluxes via overland flow, interflow, and soil erosion for the MNPK treatment were significantly (P?<?0.05) increased by 68.8, 100.6, and 63.7%, respectively. Conversely, this was significantly decreased by 182.6, ??14.1, and 49.4%, respectively, under the CNPK treatment. Correspondingly, the yield-scaled total DON losses for the MNPK and CNPK treatments were significantly increased by 78.8 and ??18.2% compared to the NPK treatment (0.33?±?0.04 kg N t^?1 grain). Therefore, long-term continuous manure application is associated with an increased risk of DON environmental pollution. Alternatively, the incorporation of crop straw can be recommended as a means of decreasing DON pollution while maintaining crop yield.     

Manure and fertilizer contributions to soil mineral nitrogen and the yield of forage maize

Fifteen field trials were conducted to evaluate soil mineral N measurement as a means for quantifying the total N supply to forage maize and so to form the basis for fertilizer recommendations on a crop-specific basis. In every trial, 4 rates of cattle manure N (nominally 0, 80, 160, 240 kg N per ha) and 4 rates of ammonium nitrate (0, 50, 100, 150 kg N per ha) were factorially combined. Soil mineral N measurements were made before manure application, at the time of maize drilling, 7-10 weeks after drilling and after harvest. Measurements on control treatments which received no manure or ammonium nitrate showed extensive net mineralisation of soil N (mean 140 kg N per ha) in the 7-10 weeks after drilling followed by a decrease due to crop uptake, and probably net immobilisation, of approximately the same amount by harvest. This net mineralisation was probably the reason why only one trial showed a significant dry-matter yield response to ammonium nitrate. Results indicated that , to be useful for N recommendations, soil mineral N measurements should be taken 7-10 weeks after drilling. Only if the amount of mineral N at this time is less than expected crop N offtake should fertilizer N be applied. A mean of around 64% of the N applied in ammonium nitrate could be accounted for in soil mineral N after harvest of the maize, although this was reduced to 24% in the single trial where a dry-matter response to ammonium nitrate was recorded.     

A model to predict crop response to applied fertilizer nutrients in heterogeneous fields

In this paper we develop a model to quantify spatial variability in indigenous soil nutrient supply and assess the impact of this heterogeneity on fertilizer use efficiency with uniform or site-specific nutrient application. Utilizing field data for wheat and rice response to applied N and cotton response to applied K, the model predicts that the magnitude of the difference in the nutrient input requirement of a heterogeneous field for site-specific versus uniform nutrient application depends on (1) a curvilinear crop response to nutrient supply and the mathematical form of the response function, (2) the degree and spatial distribution of the nonuniformity in native soil-nutrient supply as quantified by its variance and skewness, (3) the targeted yield level, and (4) the effectiveness of fertilizer-nutrient addition, quantified by the slope of the relationship between the net increase in actual nutrient supply available to the crop and the quantity of applied nutrient.     

Phosphorus and potassium cycling in a long-term no-till integrated soybean-beef cattle production system under different grazing intensities insubtropics

Long-term integrated crop-livestock system enables constant and more efficient nutrient cycling because animal, pasture and crop residues release nutrients at different rates. Therefore, appropriate management of these systems is needed to maximize benefits from nutrient cycling. The objective of this study was to evaluate how grazing intensity affected the release rates of phosphorus (P) and potassium (K) in pasture, dung and soybean residues in a no-till long-term integrated crop-livestock system. The experiment was established in 2001 on a clayey Oxisol after soybean harvest. Treatments consisted of pasture with sward heights maintained at 1020, 30 and 40 cm by different cattle stocking rates and a non-grazed (NG) treatment. Decomposition and release rates of nutrients in the pasture and dung were determined using litter bags, which were installed at soybean seeding and pasture seeding during two pasture-crop cycles (2009–2011). Lighter grazing intensities resulted in greater P release rate from pasture and dung residues. Pasture and dung residues released K at a very high rate and were not influenced by grazing intensity. The P and K released from soybean residue were not affected by grazing intensity; however, decomposition of soybean leaves was greater than of stems. Greatest rates of total P and K released were from pasture and dung residues under lighter grazing intensities and in the NG areas. Large amounts of P (~25 kg ha^?1) and K (~130–180 kg ha^?1) were cycled in a complete soybean-beef cattle integrated system and must be considered in the fertilization management.     

Effect of nitrogen,phosphorus and soil and crop residues management practices on maize (Zea mays L.) yield in ultisol of eastern Cameroon

The shortening of fallow period in several areas in tropical Africa has reduced soil fertility and exposed soils to erosion and run-off. Fertilizer application and crop conservation practices are needeed to sustain high crop yield and to conserve the natural resource base for upland crop production in the continent. Field trials were carried out to evaluate the effect of fertilizer application and soil and crop residues management practices on yield of maize (Zea mays L.) planted on a Plinthudult soil at Bertoua, Eastern Cameroon. Maize yields increased significantly with nitrogen and phosphorus fertilizer application. Under the rainfall pattern prevailing in the area, the amount of nitrogen required for maximum yield was higher in the second season. On the other hand, the amount of phosphorus required for maximum yield appeared to decrease with time. The burning of crop residues and weeds prior to planting together with no-till practive gave higher yield of maize than other soil and crop residues management practices.     

The effect of nitrogen source and crop rotation on the growth and yield of processing tomatoes

Four crop rotation and management systems were studied in 1994 and 1995 in relation to growth and yield of irrigated processing tomatoes (Lycopersicon esculentum Mill.). The four treatments were three four-year rotation systems [conventional (conv-4), low input and organic] and a two-year rotation system [conventional (conv-2)]. The four-year rotation was tomato-safflower-corn-wheat(or oats+vetch)/beans, and the two-year rotation was tomato-wheat. Purple vetch (Vicia sativa L.) was grown as a green manure cover crop preceeding tomatoes in the low input and organic systems. Nitrogen was supplied as fertilizer in the conventional systems, as vetch green manure plus fertilizer in the low input system and as vetch green manure plus turkey manure in the organic system. Tomato cv. Brigade was direct-seeded in the conventional systems and transplanted to the field in the low input and organic systems. In both years the winter cover crop was composed of a mixture of vetch and volunteer oats with N contents of 2.2% in 1994 and 2.7% (low input) or 1.8% (organic) in 1995. In 1994 yields were higher in conventionally grown tomatoes because a virus in the nursery infected the transplants used in the low input and organic systems. In 1995 tomatoes grown with the low input and conv-4 systems had similar yields, which were higher than those of tomatoes grown with the conv-2 and organic systems. N uptake by the crop was greater than 200 kg N ha^–1 for high yield (> 75 t ha^–1) and uptake rates of 3 to 6 kg N ha^–1 day^–1 during the period of maximum uptake were observed. The lower yield with the organic system in 1995 was caused by a N deficiency. The main effect of the N deficiency was a reduced leaf area index and not a reduction of net assimilation rate (NAR) or radiation use efficiency (RUE). Nitrogen deficiency was related to low concentration of inorganic N in the soil and slow release of N from the cover crop + manure. A high proportion of N from the green manure but only a low proportion of N from the manure was mineralized during the crop season. In the conventional systems, the estimated mineralized N from the soil organic matter during the crop season was around 85 kg ha^–1. A hyperbolic relationship between N content and total dry weight of aboveground biomass was observed in procesing tomatoes with adequate N nutrition. Lower yields with the conv-2 than with the conv-4 system were due to higher incidence of diseases in the two year rotation which reduced the NAR and the RUE. Residual N in the soil in Oct. (two months after the incorporation of crop residues) ranged between 90 and 170 kg N ha^–1 in the 0–90 cm profile.Department of Vegetable Crops.     

Effects of a catch crop and reduced nitrogen fertilization on nitrogen leaching in greenhouse vegetable production systems

Greenhouse vegetable cultivation has greatly increased productivity but has also led to a rapid accumulation of nitrate in soils and probably in plants. Significant losses of nitrate–nitrogen (NO₃-N) could occur after heavy N fertilization under open-field conditions combined with high precipitation in the summer. It is urgently needed to improve N management under the wide spread greenhouse vegetable production system. The objective of this study was to evaluate the effects of a summer catch crop and reduced N application rates on N leaching and vegetable crop yields. During a 2-year period, sweet corn as an N catch crop was planted between vegetable crops in the summer season under 5 N fertilizer treatments (0, 348, 522, 696, and 870 kg ha⁻¹) in greenhouse vegetable production systems in Tai Lake region, southern China. A water collection system was installed at a depth of 0.5 m in the soil to collect leachates during the vegetable growing season. The sweet corn as a catch crop reduced the total N concentration from 94 to 59 mg l⁻¹ in leached water and reduced the average soil nitrate N from 306 to 195 mg kg⁻¹ in the top 0.1-m soil during the fallow period of local farmers’ N application rate (870 kg ha⁻¹). Reducing the amount of N fertilizer and using catch crop during summer fallow season reduced total N leaching loss by 50 and 73%, respectively, without any negative effect on vegetable yields.     

Response to nitrogen application and interval between harvests in five grasses — I Dry-matter yield,nitrogen content and yield,numbers and weights of tillers,and proportion of crop fractions

Effects of five levels of applied nitrogen on field swards of each of five grasses were studied in the year of sowing, in the first full harvest year and part of the second harvest year. The plots were cut at 4-week intervals during the year of sowing; subsequently 4- and 8-week intervals between cuts were compared.Differences between grasses in dry-matter yield response to applied N were sufficiently large to suggest that commercially-important varieties should be tested at more than one level of applied N. In Melle and R v P the percentage increase in weight per tiller due to applying N was much greater, and in Aberystwyth S.24, Sabrina and Aberystwyth S.170 only slightly greater, than the percentage increase in number of tillers. Sabrina had a low number of tillers, with a negative effect of the final increment of applied N on number of tillers. The results for the five grasses in respect of number of tillers, weight per tiller, dry-matter yield, N yield and light penetration all emphasized the case for more frequent defoliation the higher the level of N applied. The application of N greatly increased the proportion of stem in the harvested herbage on 16 September 1977, evidently at least partly by reducing the proportion of stem which escaped defoliation. On that date, with the 8-week interval, the application of moderate amounts of N reduced the N content of the harvested herbage, evidently because of a large reduction in the proportion of green leaf blade and an increase in the proportions of stem and dead leaf blade.     

Soil nitrate-N levels required for high yield maize production in the North China Plain

High profile nitrate-nitrogen (N) accumulation has caused a series of problems, including low N use efficiency and environmental contamination in intensive agricultural systems. The key objective of this study was to evaluate summer maize (Zea mays L.) yield and N uptake response to soil nitrate-N accumulation, and determine soil nitrate-N levels to meet N demand of high yield maize production in the North China Plain (NCP). A total of 1,883 farmers’ fields were investigated and data from 458 no-N plots were analyzed in eight key maize production regions of the NCP from 2000 to 2005. High nitrate-N accumulation (≥172 kg N ha⁻¹) was observed in the top (0–90 cm) and deep (90–180 cm) soil layer with farmers’ N practice during maize growing season. Across all 458 no-N plots, maize grain yield and N uptake response to initial soil nitrate-N content could be simulated by a linear plus plateau model, and calculated minimal pre-planting soil nitrate-N content for maximum grain yield and N uptake was 180 and 186 kg N ha⁻¹, respectively, under no-N application conditions. Economically optimum N rate (EONR) decreased linearly with increasing pre-planting soil nitrate-N content (r ² = 0.894), and 1 kg soil nitrate-N ha⁻¹ was equivalent to 1.23 kg fertilizer-N ha⁻¹ for maize production. Residual soil nitrate-N content after maize harvest increased exponentially with increasing N fertilizer rate (P < 0.001), and average residual soil nitrate-N content at the EONR was 87 kg N ha⁻¹ with a range from 66 to 118 kg N ha⁻¹. We conclude that soil nitrate-N content in the top 90 cm of the soil profile should be maintained within the range of 87–180 kg N ha⁻¹ for high yield maize production. The upper limit of these levels would be reduce if N fertilizer was applied during maize growing season.     

Mineral fertilizers with recycled manure boost crop yield and P balance in a long-term field trial

Nutrient Cycling in Agroecosystems - Crop uptake and neglecting to apply phosphate (P) fertilizer are important reasons for P deficit in the agro-ecosystem. Recycled manure from within the system...     

A mathematical model for predicting the soil nitrogen status under varying fertilizer practices in a continuous cropping sequence

A mathematical model has been proposed for predicting the changes in soil nitrogen status due to continuous fertilization in a continuous cropping sequence. The model also enabled the prediction of the steady state of soil nitrogen for a specified fertilizer practice.The model was applied to six years nitrogen availability data of four fertilizer practices in finger millet-maize-cowpea sequence followed in the Long Term Fertilizer Experiments conducted at Tamil Nadu Agricultural University, Coimbatore, India. The agreement between the predicted soil nitrogen status by the model and the actuals was proved by employing reliability index.     

Residual effects of growing mungbean and uridbean on the yield and nitrogen uptake of a succeeding wheat crop

A two year field experiment was carried out at the Indian Agricutural Research Institute, New Delhi - 110012, India to assess the effect of mungbean (Vigna radiata L.) and uridbean (Vigna mungo L.) residues on the yield and N uptake of a succeeding wheat crop as compared to sorghum fodder. Sorghum produced 3.5–7.5 times more dry matter and removed 2–3 times more nitrogen than mungbean or uridbean during same duration (80 ± 10 days) of their growth. Without N application the grain yield of wheat following mungbean and uridbean (without residue incorporation) was 0.45 and 0.48 t ha^–1 more than the yield of wheat following sorghum fodder. These yields were equivalent to that predicted when 36 and 38 kg urea-N ha^–1, respectively, was directly applied to wheat. The residual effects of these grain legumes were higher when succeeding wheat was fertilized with 60 kg urea-N ha^–1; at this level mungbean and uridbean spared 52 and 43 kg urea-N ha^–1, respectively, in succeeding wheat. The residual effect of mungbean and uridbean further increased when their residue was incorporated in soil; with this practice they spared 94 and 115 kg urea-N ha^–1, respectively, without N application to wheat and 74 and 82 kg urea-N ha^–1, respectively, with an application of 60 kg urea-N ha^–1 to wheat.Mungbean and uridbean, without residue incorporation, increased aboveground plant-N uptake of succeeding wheat by 11.5–34.9 and 10.8–34.0 kg N ha^–1, respectively; whereas with residue incorporation, they increased aboveground plant-N content of succeeding wheat by 26.1–45.8 and 32.7–47.7 kg N ha^–1, respectively.The results of the present study indicate that there is both an indirect sparing effect and a direct residual effect of mungbean and uridbean on the nitrogen needs of succeeding wheat, more so when their residues are incorporated in soil.     

The deficiency of the ‘economic optimum’ application for evaluating models which predict crop yield response to nitrogen fertiliser

Much effort is devoted to testing N-fertiliser models against measurements of yield in N-fertiliser experiments. We show that the economic optimum application of N-fertiliser can often only be determined very imprecisely from such measurements, even when they are accurate. Hence any attempt to evaluate a simulation model by comparing simulated with experimentally determined optima, or to relate these experimental optima to other factors thought to influence yield, will be uninformative. Big differences between simulated and measured optima will occur even with good models, which may explain the apparent poor performance of some simulation models in the literature.We suggest, instead, the systematic inspection of the differences between simulated and observed yields at the levels of N-fertiliser applied in an experiment. A study of the relationship of these differences to the applied level of N-fertiliser and to other factors of interest will be a more informative method of evaluating a model, and of suggesting other factors for inclusion in it. An example of the use of the method is given.     

Using mucuna and P fertilizer to increase maize grain yield and N fertilizer use efficiency in the coastal savanna of Togo

To reduce severe soil degradation associated with agriculture an intensified land-use system is being promoted in West African countries. Most soils of the West African savanna zones are so poor that the efficiency of mineral fertilizers, if applied, is very low. For this reason and because of their high cost and unavailability, many small-scale farmers are reluctant to apply fertilizer. This work investigates a fertilizer management strategy using integrated soil fertility management with a leguminous cover crop (mucuna) so as to improve the soil fertility and increase the use efficiency of fertilizer. The experiment was conducted in the coastal savanna of Togo at Djaka Kopé. The aim was to evaluate the effectiveness of mucuna short fallow (MSF) in increasing maize grain yield through an improved use efficiency of mineral fertilizer. A 2-year maize–mucuna relay intercropping system was compared with continuous sole maize cropping. Fertilizer treatments were factorial combinations of 0, 50 and 100 kg nitrogen (N) ha^–1 and 0, 20 and 40 kg phosphorus (P) ha^–1. While maize grain yield was significantly increased by N fertilization, P did not show any important effect on grain yield. With no N and P applied, grain yield after MSF was on average 40% (572 kg ha^–1) higher than without. The response to N was much greater than the response to MSF, indicating that N was undoubtedly the key element for maize yield building. P fertilization and MSF together positively influenced the apparent N recovery fraction (NRF). N uptake alone did not reflect on its own the yield obtained, and the relationship between grain yield and N uptake is shifted by MSF, with the grain yield increase per unit of N uptake being higher with than without MSF. Combining MSF and P fertilization may therefore lead to improved N use efficiency, making the application of fertilizer N (lower rates) more attractive to small-scale farmers.     

Estimating the crop response to fertilizer nitrogen residues in long-continued field experiments

Knowledge of the cumulated effect of long-continued nitrogen (N) inputs is important for both agronomic and environmental reasons. However, only little attention has been paid to estimate the crop response to mineral fertilizer N residues. Before interpreting estimates for the crop response to previous N input rates, the experimental design for testing needs to be examined. Experimental designs that suspend the customary N inputs, leaving the test crop unfertilized, ignore any interaction between the rate of N applied in the past and the rate applied in the test year. We estimated the interaction using data from five long-continued field experiments on mineral and organic N input rates where the main plots were subdivided for incremental rates of mineral N fertilizer in the test year. The interaction between N applied in the past and in the test year significantly affected grain yield and N offtake when the residual effect originated from organic applications, but the interaction was not significant when mineral N fertilizer had been used in the past, making the residual effect of N applied in the past additive to the effect of N applied in the test year. The dry matter (DM) grain yield of spring barley decreased by an average of 5?kg?DM/ha and the grain N offtake by 46?g?N/ha for a decrease in the annual mineral N rate of 1?kg?N/ha applied for more than three decades. Although statistically significant, the crop response to mineral fertilizer N residues was of minor importance when compared with the residual effect of organic inputs.     

Evaluation of production yield and thermal processing of switchgrass as a bio-energy crop for the Mediterranean region

Switchgrass, a warm-season perennial grass, could play an important role for Europe in supplying sustainably produced lignocellulosic biomass, as its establishment cost is low and its productivity high under low input conditions. The aim of this study was to evaluate the adaptability and biomass productivity of switchgrass under the Greek climatic conditions and furthermore its suitability for heat and electricity applications, by performing fuel analyses, pyrolysis and combustion tests. Three-year field trials with different irrigation and fertilization levels showed that each level of irrigation had a significant effect on dry matter yields, while nitrogen effect was not pronounced. Yields were similar in the second and third year and ranged from 15.4% to 24 tons/ha.Fuel characterization showed a high volatile content and calorific value, whereas low ash, sulphur, nitrogen and chlorine contents. Ashes were rich in Si, K and P and some micronutrients, such as Zn. The ash fusion temperatures of the stems, which were richer in alkali, were low for combustion processes, revealing slagging/fouling problems in boilers without crop pre-treatment. However, their ash content was very low. The thermochemical reactivity of the stems was higher than that of the leaves, especially in air. The greater amount of minerals in the leaves inhibited the reaction rates in either nitrogen or air atmospheres. A first-order parallel reactions model for pyrolysis and a power low model for combustion fitted the experimental results accurately and kinetic parameters were derived. Irrigation/fertilization treatment had a positive effect on the combustion performance of the stems.     

The effect of fertilizer placement on nitrogen uptake and yield of wheat and maize in Chinese loess soils

Field trials were carried out to study the fate of¹⁵N-labelled urea applied to summer maize and winter wheat in loess soils in Shaanxi Province, north-west China. In the maize experiment, nitrogen was applied at rates of 0 or 210 kg N ha^–1, either as a surface application, mixed uniformly with the top 0.15 m of soil, or placed in holes 0.1 m deep adjacent to each plant and then covered with soil. In the wheat experiment, nitrogen was applied at rates of 0, 75 or 150 kg N ha^–1, either to the surface, or incorporated by mixing with the top 0.15 m, or placed in a band at 0.15 m depth. Measurements were made of crop N uptake, residual fertilizer N and soil mineral N. The total above-ground dry matter yield of maize varied between 7.6 and 11.9 t ha^–1. The crop recovery of fertilizer N following point placement was 25% of that applied, which was higher than that from the surface application (18%) or incorporation by mixing (18%). The total grain yield of wheat varied between 4.3 and 4.7 t ha^–1. In the surface applications, the recovery of fertilizer-derived nitrogen (25%) was considerably lower than that from the mixing treatments and banded placements (33 and 36%). The fertilizer N application rate had a significant effect on grain and total dry matter yield, as well as on total N uptake and grain N contents. The main mechanism for loss of N appeared to be by ammonia volatilization, rather than leaching. High mineral N concentrations remained in the soil at harvest, following both crops, demonstrating a potential for significant reductions in N application rates without associated loss in yield.