Separating nitrogen fertilizer and irrigation water application in an alternating furrow irrigation system for maize production

The efficient use of water and nitrogen represents a primary concern to agricultural production in Northwest China. A 2-year field experiment was conducted to assess the separation of nitrogen (N) fertilizer and irrigation water with alternating furrow irrigation (SNWAFI) in a maize (Zea mays L.) production system. Irrigation water use efficiency and nitrogen use efficiency with SNWAFI were generally greater than with conventional irrigation and fertilization (CIF). Response surfaces indicated that maximum maize yields were obtained with 238 kg urea-N ha^?1 and 106 mm irrigation water in 2008 and 244 kg urea-N ha^?1 and 95 mm of irrigation water in 2009. When the predicted yields were highest (6,384 and 6,549 kg ha^?1), water use efficiency, N uptake, and N use efficiency were greater with SNWAFI than CIF. Conversely, soil NO₃–N change during maize growing season decreased with SNWAFI compared CIF. With SNWAFI, optimizing irrigation water and N fertilizer rates can maximize yield, save irrigation water, and reduce N leaching.     

Influence of cultivars and nitrogen rates on the residual effects of potassium applications to preceding cotton on maize

The long-term residual effects of K application rates and cultivars for preceding cotton (Gossypium hirsutum L.) on subsequent maize (Zea mays L.) and the influence of N rates applied to preceding cotton and to maize on the residual K effects were examined on maize under no-tillage in the United States. Two field experiments were conducted on a no-till Loring silt loam at Jackson, TN during 1995–2008 with N rates (90 and 179 kg ha^?1) × K rates (28, 56, and 84 kg ha^?1) and cotton cultivars (determinate and indeterminate) × K rates (56 and 112 kg ha^?1) as the treatments, respectively, in the preceding cotton seasons. Maize was planted under no-tillage on the preceding cotton experiments without any K application during 2009 through 2011. The residual effects of K rates applied to preceding cotton on soil K levels were significantly influenced by the N rates applied to preceding cotton and to maize when the data were combined from 2008 to 2011. Relative to the standard N management practices of 168 kg N ha^?1 for maize and 90 kg N ha^?1 for preceding cotton, the higher N application rate 269 kg N ha^?1 to maize and 179 kg N ha^?1 to preceding cotton reduced the residual effects of K rates on soil K. However, cultivar for preceding cotton did not affect the residual effects of K fertilizer on soil K fertility, leaf K nutrition, plant growth, or grain yield of subsequent maize on a high K field.     

Evaluation of Agriglass as an Environment Friendly Slow Release Fertilizer

Six different agriglass compositions of the (P₂O₅-SiO₂-K₂O) system were prepared with the addition of some oxides; Fe₂O₃, MnO₂, ZnO, CuO. Glasses were synthesized by a melting quenching technique at 1150 ^°C. The chemical activity of glass grains of different diameters (0.5 and 1 mm) was estimated by measuring available K₂O % by a flame photometer, and P₂O₅ % by a spectrophotometer, in conditions simulating the plant root zone by shaking in DTPA solution (NH₄HCO₃-DTPA: ammonium bicarbonate diethylenetriaminepentaacetic acid) for 30 min. The results showed that PS1 glass with main composition (55 P₂O₅, 5 SiO₂, 30 K₂O, 5 Fe₂O₃, 5CuO) wt.%, produced high release nutrient values. The other chemical activity tests were established to evaluate the PS1 glass by shaking in distilled water for 0.5, 1, 2 and 3 hours, and immersion in DTPA solution and 2 wt% citric acid solutions for 1, 2, 3 and 4 months. A greenhouse experiment was performed to evaluate two rates of PS1 agriglass (PS1R1 and PS1R2) compared with the recommended rate of ordinary mineral fertilizers (MF). Although, the effect of MF is higher than both vitreous fertilizer rates in the measurement of 100 grains weight, grains and Stover weight, the application of agriglass with high rate (PS1R2) gave higher results than that of MF in the measurements of ears weight, plant height, and crop weight. It has been found that PS1 glass can be used in practice for maize as an environmentally safe fertilizer.     

Simulating impact of seasonal climatic variation on the response of maize (Zea mays L.) to inorganic fertilizer in sub-humid Ghana

Under low input subsistence farming systems, increased pressure on land use and decreased fallow periods have led to a decline in soil productivity. The soils in sub-humid region of Ghana are generally poor and require mineral fertilizer to increase crop productivity. This paper presents the use of Agricultural Production Systems sIMulator (APSIM) to simulate the long term influence of nitrogen (N) and phosphorus (P) on maize (Zea mays L.) yield in Sub-humid Ghana. The APSIM model was evaluated at two sites in Ejura, on a rainfed experiment carried out on maize in 2008 major and minor seasons, under various nitrogen and phosphorus rates. The model was able to reproduce the response of maize to water, N and P, and hence simulated maize grain yields with a coefficient of correlation (R²) of 0.90 and 0.88 for Obatanpa and Dorke cultivars, respectively. A 21-year long term simulation, with different rates of N and P mineral fertilizer application, revealed that moderate application of N (60?kg?N?ha^?1) and 30?kg P ha^?1 improves both the long term average and the minimum yearly guaranteed yield. Variability in grain yield increased with increasing application of N fertilizer in both seasons. Treatments with P fertilizer application shows a similar trend for the major season and reverse trend for the minor season, thereby suggesting an interactive effect with rainfall amounts and distribution. Application of 30?kg P ha^?1 significantly increased the response to N. The response to mineral fertilizer (N and P) applications varied between seasons, suggesting the need to have a range of fertilizer recommendations to be applied based on seasonal weather forecast.     

Nitrous oxide emissions and herbage accumulation in smooth bromegrass pastures with nitrogen fertilizer and ruminant urine application

Agricultural soils contribute significantly to nitrous oxide (N₂O) emissions, but little data is available on N₂O emissions from smooth bromegrass (Bromus inermis Leyss.) pastures. This study evaluated soil N₂O emissions and herbage accumulation from smooth bromegrass pasture in eastern Nebraska, USA. Nitrous oxide emissions were measured biweekly from March to October in 2011 and 2012 using vented static chambers on smooth bromegrass plots treated with a factorial combination of five urea nitrogen (N) fertilizer rates (0, 45, 90, 135, and 180 kg ha^?1) and two ruminant urine treatments (distilled water and urine). Urine input strongly affected daily and cumulative N₂O emissions, but responses to N fertilizer rate depended on growing season rainfall. In 2011, when rainfall was normal, cumulative N₂O emissions increased exponentially with N fertilizer rate. In 2012, drought reduced daily and cumulative N₂O emission responses to N fertilizer rate. Herbage accumulation ranged from 4.46 Mg ha^?1 in unfertilized pasture with distilled water to 16.01 Mg ha^?1 in pasture with 180 kg N ha^?1 and urine in 2011. In 2012, plots treated with urine had 2.2 times more herbage accumulation than plots treated with distilled water but showed no response to N fertilizer rate. Total applied N lost as N₂O ranged from 0–0.6 to 0.5–1.7 % across N fertilizer rates in distilled water and urine treatments, respectively, and thus, support the Intergovernmental Panel on Climate Change default direct emission factors of 1.0 % for N fertilizer additions and 2.0 % for urine excreted by cattle on pasture.     

Combining hill-placed manure and mineral fertilizer enhances maize productivity and profitability in northern Benin

Throughout much of Sub-Saharan Africa (SSA), maize production is characterized by low productivity due to the scarce availability and use of external inputs and recurrent droughts exacerbated by climate variability. Within the integrated soil fertility management (ISFM) framework, there is thus a need for optimizing the application of fertilizers and manure to better use the limited nutrient resources and increase crop yield and farmer income. An on-station experiment was conducted in Northern Benin over a 4-year period to evaluate the effect of hill placement of mineral fertilizer and manure on maize yields and soil chemical properties. The treatments consisted in the combination of three rates of manure (0 (NM), 3 (3M) and 6 (6M) Mg ha^?1) and three levels of fertilizer (0% (NF), 50% (50F) and 100% (100F) of the rate recommended by extension (76 kg N + 13.1 kg P + 24.9 K ha^?1)). On average across the fertilizer rates, hill-placement of manure significantly improved soil organic carbon content, available P and exchangeable K after 4 years by up to 124, 166 and 77%, respectively, compared to the initial values. As a result of the nutrient inputs and improved soil properties, yields increased steadily over time for all manure and fertilizer combinations. Value-cost ratios and benefit–cost ratios were >2 and generally as good or even better for treatments involving 50F compared to NF or 100F. Although applying half the recommended rate of fertilizer without manure as currently done by many farmers appears to make economic sense, this practice is unlikely to be sustainable in the long term. Substituting 50F for 3M or complementing 50F with 3M are two possible strategies that are compatible with the precepts of ISFM and provide returns on investment at least as good as the current practice. However, this will require greater manure production, made possible in part by the increased stover yields, and access to means of transportation to deliver the manure to the fields.     

Leaching losses from Kenyan maize cropland receiving different rates of nitrogen fertilizer

Meeting food security requirements in sub-Saharan Africa (SSA) will require increasing fertilizer use to improve crop yields, however excess fertilization can cause environmental and public health problems in surface and groundwater. Determining the threshold of reasonable fertilizer application in SSA requires an understanding of flow dynamics and nutrient transport in under-studied, tropical soils experiencing seasonal rainfall. We estimated leaching flux in Yala, Kenya on a maize field that received from 0 to 200 kg ha^?1 of nitrogen (N) fertilizer. Soil pore water concentration measurements during two growing seasons were coupled with results from a numerical fluid flow model to calculate the daily flux of nitrate-nitrogen (NO₃ ^?-N). Modeled NO₃ ^?-N losses to below 200 cm for 1 year ranged from 40 kg N ha^?1 year^?1 in the 75 kg N ha^?1 year^?1 treatment to 81 kg N ha^?1 year^?1 in the 200 kg N ha^?1 treatment. The highest soil pore water NO₃ ^?-N concentrations and NO₃ ^?-N leaching fluxes occurred on the highest N application plots, however there was a poor correlation between N application rate and NO₃ ^?-N leaching for the remaining N application rates. The drought in the second study year resulted in higher pore water NO₃ ^?-N concentrations, while NO₃ ^?-N leaching was disproportionately smaller than the decrease in precipitation. The lack of a strong correlation between NO₃ ^?-N leaching and N application rate, and a large decrease in flux between 120 and 200 cm suggest processes that influence NO₃ ^?-N retention in soils below 200 cm will ultimately control NO₃ ^?-N leaching at the watershed scale.     

Preparation of superabsorbent slow release nitrogen fertilizer by inverse suspension polymerization

A superabsorbent, slow release nitrogen fertilizer (SSRNF) was prepared by inverse suspension polymerization of partially neutralized acrylic acid using N,N′‐methylene bisacrylamide as a crosslinker and ammonium persulfate as an initiator in the presence of urea. The polymer was characterized using infrared spectral analysis, and network structural parameters such as molecular weight between crosslinks (M_c) and crosslink density (q) were calculated. The effects of reaction conditions, such as reaction time, reaction temperature, initiator, crosslinker and the degree of neutralization of acrylic acid, on water absorbency were investigated. The nitrogen content of SSRNF synthesized under optimal conditions was 22.7%, and the water absorbencies were about 965 g g^?1 in distilled water and 185 g g^?1 in tap water. The nitrogen slow release behaviors of the SSRNF in water and water retention capacity of soil with the SSRNF were also investigated. A possible slow release mechanism was proposed and the release rate constant K and the diffusion coefficient D of urea in the hydrogel was calculated. The results showed that the product not only had good slow release properties but also excellent soil moisture preservation capacity, which could effectively improve the utilization of fertilizer and water resources simultaneously. Therefore, the SSRNF is a multifunctional water managing material, which would find application in agriculture and horticulture, especially in drought‐prone areas where the availability of water is limited. Copyright © 2006 Society of Chemical Industry     

Response of maize (Zea mays) to phosphorus application on basaltic soils in Northwestern Cameroon

A field trial was conducted on two P sorptive, basaltic soils commonly used for maize production in Northwestern Cameroon. The objective was to determine the maintenance P rates required for adequate P supply in the soils for maize after initial capital dressing applications of P (0, 22, 44, 88 and 132 kg ha^-1) in 1991. These were followed by three supplementary P rates – 0, 44 and 88 kg ha^-1 in 1992. Three crops of maize (cv COCA) were grown to monitor the availability of the residual P. Experimental design was randomized complete block with four replications in 1991 and a split-plot in 1992 and 1993. The soils at the experimental sites were rich in organic P which formed 67% and 57% of total P at Mfonta and Babungo respectively. Laboratory P sorption studies indicated high P requirements by the basaltic soils used in the study. The amounts of P sorbed to attain 0.2 ug g^-1 in soil solution were 1200 ug g^-1 at Mfonta and 600 ug g^-1 at Babungo. In spite of these high P sorption capacities, significant responses to small rates of P application were observed. It was concluded that a sizable proportion of P released from organic P mineralization was used to satisfy P sorption capacity of the soils, resulting in maize response to small rates of fertilizer P application. Residual P effects on maize yield were related to applied P. Bray 1 extractable soil P was weakly related to grain yields (r = 0.136 at Mfonta and r = 0.186 at Babungo). A critical value of 5.5 mg kg^-1 Bray 2 extractable P in the soil was established for maize at Mfonta site. About 44 kg P ha^-1 was recommended for maize at this site when Bray 2 soil P test was below this critical value.     

Comparative short-term effects of different quality organic resources on maize productivity under two different environments in Zimbabwe

Major challenges for combined use of organic and mineral nutrient sources in smallholder agriculture include variable type and quality of the resources, their limited availability, timing of their relative application and the proportions at which the two should be combined. Short-term nutrient supply capacity of five different quality organic resources ranging from high to low quality, namely Crotalaria juncea, Calliandra calothyrsus, cattle manure, maize stover and Pinus patula sawdust were tested in the field using maize as a test crop. The study was conducted on two contrasting soil types at Makoholi and Domboshawa, which fall under different agro-ecological regions of Zimbabwe. Makoholi is a semi-arid area (<650 mm yr⁻¹) with predominantly coarse sandy soils containing approximately 90 g kg⁻¹ clay while Domboshawa (>750 mm yr⁻¹) soils are sandy-clay loams with 220 g kg⁻¹ clay. Each organic resource treatment was applied at low (2.5 t C ha⁻¹) and high (7.5 t C ha⁻¹) biomass rates at each site. Each plot was sub-divided into two with one half receiving 120 kg N ha⁻¹ against zero in the other. At Makoholi, there was a nine-fold increase in maize grain yield under high application rates of C. juncea over the unfertilized control, which yielded only 0.4 t ha⁻¹. Combinations of mineral N fertilizer with the leguminous resources and manure resulted in between 24% and 104% increase in grain yield against sole fertilizer, implying an increased nutrient recovery by maize under organic–mineral combinations. Maize biomass measured at 2 weeks after crop emergence already showed treatment differences, with biomass yields increasing linearly with soil mineral N availability (R ² = 0.75). This 2-week maize biomass in turn gave a positive linear relationship (R ² = 0.82) with grain yield suggesting that early season soil mineral N availability largely determined final yield. For low quality resources of maize stover and sawdust, application of mineral N fertilizer resulted in at least a seven-fold grain yield increase compared with sole application of the organic resources. Such nutrient combinations resulted in grain harvest indices of between 44% and 48%, up from a mean of 35% for sole application, suggesting the potential of increasing maize productivity from combinations of low quality resources with mineral fertilizer under depleted sandy soils. At Domboshawa, grain yields averaged 7 t ha⁻¹ and did not show any significant treatment differences. This was attributed to relatively high levels of fertility under the sandy-clay loams during this first year of the trial implementation. Differences in N supply by different resources were only revealed in grain and stover uptake. Grain N concentration from the high quality leguminous resources averaged 2% against 1.5% from sawdust treatments. We conclude that early season soil mineral N availability is the primary regulatory factor for maize productivity obtainable under poor sandy soils. Maize biomass at 2 weeks is a potential tool for early season assessment of potential yields under constrained environments. However, the likely impact on system productivity following repeated application of high N-containing organic materials on different soil types remains poorly understood.     

Fate of fertilizer 15N in intensive ridge cultivation with plastic mulching under a monsoon climate

Reducing nitrogen (N) leaching to groundwater requires an improved understanding of the effect of microtopography on N fate. Because of the heterogeneity between positions, ridge tilled fields, frequently used in intensive agriculture, should be treated as two distinct management units. In this study, we measured N dynamics in plastic-mulched ridges and bare furrows with the goal of developing more sustainable agricultural practices with optimal gains, namely crop production versus limited impacts on water quality. We investigated: (1) biomass production; (2) crop N uptake; (3) N retention in soil; and (4) N leaching using ¹⁵N fertilizer in a radish crop. Broadcast mineral N fertilizer application prior to planting resulted in high total leaching losses (of up to 390 N kg ha^?1). The application of plastic mulch in combination with local fertilizer management did not help to reduce N leaching. At all fertilizer N rates, the mean NO₃ ^? concentrations in seepage water were found to be above the WHO drinking water standard of 50 mg NO₃ ^? l^?1. To reduce NO₃ ^? leaching, we recommend: (1) decreasing the fertilizer N rates to a maximum of 150 kg N ha^?1; (2) applying fertilizer N in 3–4 split applications according to the plant’s N needs; (3) applying fertilizer N to the ridges (after their formation) to avoid losses from the furrows; and (4) increasing the soil organic matter content to enhance the water and nutrient retention by covering the furrows with plant residues.     

Uptake of fertilizer and soil nitrogen by ryegrass swards during spring and mid-season

Double-labelled¹⁵N ammonium nitrate was used to determine the uptake of fertilizer and soil N by ryegrass swards during spring and mid-season. The effects of water stress (40% of mean rainfall v 25 mm irrigation per 25 mm soil water deficit) and the rate of application of N in the spring (40 v 130 kg ha^–1) on the recovery of 130 kg N ha^–1 applied in mid-season were also evaluated. Apparent recovery of fertilizer N (uptake of N in the fertilized plot minus that in the control expressed as a percentage of the N applied) was 95 and 79% for fertilizer N applied in the spring at rates of 40 and 130 kg ha^–1, respectively. Actual recovery of the fertilizer N assessed from the uptake of¹⁵N was only 31 and 48%, respectively. The uptake of soil N by the fertilized swards was substantially greater than that by the control. However, the increased uptake of soil N was always less than the amount of fertilizer N retained in or lost from the soil. Broadly similar patterns for the uptake of fertilizer and soil N were observed during mid-season. Uptake of N in mid-season was highest for swards which received 40 kg N ha^–1 in the spring and suffered minimal water stress during this period. Application of 130 kg N ha^–1 in spring reduced the uptake of N in mid-season to an extent similar to that arising from water stress. Only 1.8 to 4.2 kg ha^–1 (3 to 10%) of the N residual from fertilizer applied in the spring was recovered during mid-season. Laboratory incubation studies suggested that only a small part of the increased uptake of soil N by fertilized swards could be attributed to increased mineralisation of soil N induced by addition of fertilizer. It is considered that the increased uptake of soil N is partly real but mostly apparent, the latter arising from microbially mediated exchange of inorganic¹⁵N in the soil.     

Nitrogen uptake efficiency in maize production using irrigation water high in nitrate

In order to achieve efficient use of nitrogen (N) and minimize pollution potentials, producers of irrigated maize (Zea mays L.) must make the best use of N from all sources. This study was conducted to evaluate crop utilization of nitrate in irrigation water and the effect N fertilizer has on N use efficiencies of this nitrate under irrigated maize production. The study site is representative of a large portion of the Central Platte Valley of Nebraska where ground water nitrate-N (NO₃-N) concentrations over 10 mg L^–1 are common. Microplots were established to accommodate four fertilizer N rates (0, 50, 100, and 150 kg ha^–1) receiving irrigation water containing three levels of NO₃-N (0, 10, 20 mg L^–1). Stable isotope¹⁵N was applied as a tracer in the irrigation water for treatments containing 10 and 20 mg L^–1 NO₃-N. Plots that did not receive nitrate in the irrigation water where tagged with¹⁵N fertilizer as a sidedress treatment. Sidedressed N fertilizer significantly reduced irrigation-N uptake efficiencies. When residual N uptake is added to first year plant usage, total irrigation NO₃-N uptake efficiencies are similar to total sidedress N fertilizer uptake efficiencies for our cropping system over the two year period. Efficiency of irrigation-N use depends on crop needs and availability of N from other sources during the irrigation season.     

Supramolecular recognition of functional magnesium tetraphenylporphyrin with pyrrolidine for SO2 capture

Supramolecular recognition of functional magnesium tetraphenylporphyrin (MgTPP) with pyrrolidine for SO₂ capture was investigated in CH₂Cl₂ by steady-state fluorescence and UV-vis absorption spectroscopic techniques. The UV-vis spectra showed that the interaction of MgTPP with pyrrolidine resulted in red shift of 2 nm for MgTPP Soret absorption band. Once introduced, SO₂ competes with MgTPP for pyrrolidine, which eventually leads to the release of MgTPP. The fluorescence spectra suggested that MgTPP interacted with pyrrolidine to form 1: 1 molecular adducts, and showed that the binding of MgTPP with pyrrolidine with the association constants (Kassoc) of (0.86 to 1.19) is not only exothermic but enthalpy-driven with ΔH=?15.805 kJ mol^?1, ΔS=?52.727 J mol^?1 K¹, and ΔG=?214.444 J mol^?1 at T=296.15 K.     

Integrated management practices significantly affect N2O emissions and wheat–maize production at field scale in the North China Plain

In the North China Plain, a field experiment was conducted to measure nitrous oxide (N₂O) and methane (CH₄) fluxes from a typical winter wheat–summer maize rotation system under five integrated agricultural management practices: conventional regime [excessive nitrogen (N) fertilization, flood irrigation, and rotary tillage before wheat sowing; CON], recommended regime 1 (balanced N fertilization, decreased irrigation, and deep plowing before wheat sowing; REC-1), recommended regime 2 (balanced N fertilization, decreased irrigation, and no tillage; REC-2), recommended regime 3 (controlled release N fertilizer, decreased irrigation, and no tillage; REC-3), and no N fertilizer (CK). Field measurements indicated that pulse emissions after N fertilization and irrigation contributed 19–49 % of annual N₂O emissions. In contrast to CON (2.21 kg N₂O-N ha^?1 year^?1), the other treatments resulted in significant declines in cumulative N₂O emissions, which ranged from 0.96 to 1.76 kg N₂O-N ha^?1 year^?1, indicating that the recommended practices (e.g., balanced N fertilization, controlled release N fertilizer, and decreased irrigation) offered substantial benefits for both sustaining grain yield and reducing N₂O emissions. Emission factors of N fertilizer were 0.21, 0.22, 0.23, and 0.37 % under CON, REC-1, REC-3, and REC-2, respectively. Emissions of N₂O during the freeze–thaw cycle period and the winter freezing period accounted for 9.7 and 5.1 % of the annual N₂O budget, respectively. Thus, we recommend that the monitoring frequency should be increased during the freeze–thaw cycle period to obtain a proper estimate of total emissions. Annual CH₄ fluxes from the soil were low (?1.54 to ?1.12 kg CH₄-C ha^?1 year^?1), and N fertilizer application had no obvious effects on CH₄ uptake. Values of global warming potential were predominantly determined by N₂O emissions, which were 411 kg CO₂-eq ha^?1 year^?1 in the CK and 694–982 kg CO₂-eq ha^?1 year^?1 in the N fertilization regimes. When comprehensively considering grain yield, global warming potential intensity values in REC-1, REC-2, and REC-3 were significantly lower than in CON. Meanwhile, grain yield increased slightly under REC-1 and REC-3 compared to CON. Generally, REC-1 and REC-3 are recommended as promising management regimes to attain the dual objectives of sustaining grain yield and reducing greenhouse gas emissions in the North China Plain.     

Residual phosphorus effects and nitrogen × phosphorus interactions in soybean–maize rotations on a P-deficient Ferralsol

Legume-cereal rotations are an essential component of integrated soil fertility management in low-input cropping systems, but strategies are needed to increase phosphorus (P) fertilizer use efficiency in such systems. These may include preferential targeting of P to one of the crops in the rotation cycle, the use of P-efficient genotypes, and the optimization of the rates of P fertilizer used. A field trial was conducted to evaluate the effects of increasing P fertilizer rates (0, 11, 22 and 44 kg P ha^?1, added as triple super phosphate) applied to three soybean genotypes grown on a P-deficient Ferralsol, on the nitrogen (N) and P nutrition of a subsequent maize crop. In addition, a greenhouse trial was set up to assess N, P and other rotation effects of three soybean genotypes on a subsequent maize crop relative to a maize–maize rotation at high and low P supply. In the field trial, soybean did not respond to increasing P rates, but residual P effects improved maize grain yields by up to 90 %. Ear leaf (field trial) and shoot (pot trial) P concentrations increased by applying N to maize, demonstrating important N × P interactions. The pot trial did not reveal a positive rotation effect of soybean on maize beyond the mere N-benefit, showing that soybean was not able to improve P availability to maize after correcting for the N-effect. No variation in rotation effects on maize among soybean genotypes was observed. Because of the absence of effects of the soybean crop on P availability to maize, opportunities to increase P fertilizer use efficiency in soybean–maize rotations mainly reside in maximizing P uptake by each crop separately and in matching P fertilizer rates with crop demand.     

Carbon sequestration in soil aggregates under different crop rotations and nitrogen fertilization in an inceptisol in southeastern Norway

Effects of crop rotation and fertilization (nitrogen and manure) on concentrations of soil organic carbon (SOC) and total soil nitrogen (TSN) in bulk soil and in soil aggregates were investigated in a long-term field experiment established in 1953 at Ås, Norway. The effect of these management practices on SOC sequestration was estimated. The experiment had three six-course rotations: (I) continuous spring grain, (II) spring grain for 3 years followed by root crops for 3 years, and (III) spring grain for 2 years followed by meadow for 4 years. Three fertilizer treatments compared were: (A) 30–40 kg N ha^–1; (B) 80–120 kg N ha^–1; and (C) a combination of B and 60 Mg farmyard manure (FYM) ha^–1. All plots received a basal rate of PK fertilizer. Soil samples from these treatments were collected in autumn 2001 and analyzed for aggregate size, SOC and TSN concentrations. There were significant increases in 0.6–2 mm and < 0.6 mm aggregate size fractions, and reduction in the 6–20 mm and the > 20 mm sizes for rotation III only. There were also significant differences among rotations with regard to water stable aggregation. The order of increase in stability was II < I < III. Fertilizer treatment had no effect on aggregation or aggregate size distribution, but there was a slight tendency of increased stability with the application of FYM. Aggregate stability increased with increasing concentration of SOC (r2 = 0.53). The SOC and TSN concentrations in bulk soil were significantly higher in rotation III than in rotations II and I. Application of FYM increased SOC and TSN concentrations significantly in the 0–10 cm soil depth, but there were few significant differences between fertility treatments A and B. There was a trend of increase in concentration of SOC and TSN with decreasing aggregate size, but significant differences in these parameters in different aggregate size fractions were found only in few cases. The SOC and TSN concentrations were higher in >0.25 mm than in < 0.25 mm aggregates. The SOC sequestration rate was 77–167 kg SOC ha^–1 yr^–1 by increasing the N rate and 40–162 kg SOC ha^–1 yr^–1 by applying FYM. The SOC sequestration rate by judicious use of inorganic fertilizer was the greatest in the grain–meadow rotation, while that by application of FYM was the greatest in the all grain rotation.     

The carbon footprint of maize production as affected by nitrogen fertilizer and maize-legume rotations

Studies on the sustainability of crop production systems should consider both the carbon (C) footprint and the crop yield. Knowledge is urgently needed to estimate the C cost of maize (Zea mays L.) production in a continuous monoculture or in rotation with a leguminous crop, the popular rotation system in North America. In this study, we used a 19-year field experiment with maize under different levels of synthetic N treatments in a continuous culture or rotation with forage legume (Alfalfa or red clover; Medicago sativa L./Trifolium pratense L.) or soybean (Glycine max L. Merr) to assess the sustainability of maize production systems by estimating total greenhouse gas (GHG) emissions (kg?CO₂ eq?ha^?1) and the equivalent C cost of yield or C footprint (kg?CO₂ ?eq?kg^?1?grain). High N application increased both total GHG emissions and the C footprint across all the rotation systems. Compared to continuous maize monoculture (MM), maize following forage (alfalfa or red clover; FM) or grain (soybean; SM) legumes was estimated to generate greater total GHG emissions, however both FM and SM had a lower C footprint across all N levels due to increased productivity. When compared to MM treated with 100?kg?N?ha^?1, maize treated with 100?kg?N?ha^?1, following a forage legume resulted in a 5?% increase in total GHG emissions while reducing the C footprint by 17?%. Similarly, in 18 out of the 19-year period, maize treated with 100?kg?N?ha^?1, following soybean (SM) had a minimal effect on total GHG emissions (1?%), but reduced the C footprint by 8?%. Compared to the conventional MM with the 200?kg?N?ha^?1 treatment, FM with the 100?kg?N?ha^?1 treatment had 40?% lower total GHG emissions and 46?% lower C footprint. Maize with 100?kg?N?ha^?1 following soybean had a 42?% lower total GHG emissions and 41?% lower C footprint than MM treated with 200?kg?N?ha^?1. Clearly, there was a trade-off among total GHG emissions, C footprint and yield, and yield and GHG emissions or C footprint not linearly related. Our data indicate that maize production with 100?kg?N?ha^?1 in rotation with forage or grain legumes can maintain high productivity while reducing GHG emissions and the C footprint when compared to a continuous maize cropping system with 200?kg?N?ha^?1.     

Nitrogen balances in farmers fields under alternative uses of a cover crop legume: a case study from Nicaragua

Canavalia brasiliensis (canavalia), a drought tolerant legume, was introduced into the smallholder traditional crop-livestock production system of the Nicaraguan hillsides as green manure to improve soil fertility or as forage during the dry season for improving milk production. Since nitrogen (N) is considered the most limiting nutrient for agricultural production in the target area, the objective of this study was to quantify the soil surface N budgets at plot level in farmers fields over two cropping years for the traditional maize/bean rotation and the alternative maize/canavalia rotation. Mineral fertilizer N, seed N and symbiotically fixed N were summed up as N input to the system. Symbiotic N₂ fixation was assessed using the ¹⁵N natural abundance method. Nitrogen output was quantified as N export via harvested products. Canavalia derived in average 69% of its N from the atmosphere. The amount of N fixed per hectare varied highly according to the biomass production, which ranged from 0 to 5,700 kg ha^?1. When used as green manure, canavalia increased the N balance of the maize/canavalia rotation but had no effect on the N uptake of the following maize crop. When used as forage, it bears the risk of a soil N depletion up to 41 kg N ha^?1 unless N would be recycled to the plot by animal manure. Without N mineral fertilizer application, the N budget remains negative even if canavalia was used as green manure. Therefore, the replenishment of soil N stocks by using canavalia may need a few years, during which the application of mineral N fertilizer needs to be maintained to sustain agricultural production.     

Effects of rainfall and fertilizer types on nitrogen and phosphorus concentrations in surface runoff from subtropical tea fields in Zhejiang, China

The increasing input of fertilizers in tea (Camellia sinensis L.) fields may contribute to the deterioration of surface water quality. A plot study was conducted over a 2-year period (2010?C2011) to evaluate the effects of rainfall and fertilizer types on nitrogen (N) and phosphorus (P) concentrations in surface runoff from tea fields. Studies were arranged on slope of 18?% of red clay at a subtropical tea fields in Tiaoxi watershed of Zhejiang province, southeast China. Organic (OF), slow-release (SRF), and conventional chemical fertilizers were applied to different plots at rates of 248?kg?N?ha^?1 and 125.2?kg?P?ha^?1 in 2010 and 300?kg?N?ha^?1 and 100?kg?P?ha^?1 in 2011. Rainfall amounts showed statistically significant correlations with concentrations of TN and TP in runoff water from all fertilized treatments. Although equivalent N and P were applied in each fertilized treatment, the OF treatment had the lowest annual arithmetic mean concentration of total N in runoff in 2010 (6.1?mg?L^?1) and was amongst the lowest in 2011 (9.2?mg?L^?1) with concentration statistically similar to SRF (9.0?mg?L^?1). The SRF treatment had the lowest annual arithmetic mean concentration of total P in runoff in 2010 (1.50?mg?L^?1), while few differences were observed in concentration of total P between fertilized treatments in 2011. The research results suggested that replacement of conventional chemical fertilizers with organic or slow-release fertilizers in tea fields could reduce N and P losses while maintaining tea yields.