Nitrogen balance in dryland agroecosystem in response to tillage,crop rotation,and cultural practice

Accounting of N inputs and outputs and N retention in the soil provides N balance that measures agroecosystem performance and environmental sustainability. Because of the complexity of measurements of some N inputs and outputs, studies on N balance in long-term experiments are scanty. We examined the effect of 8 years of tillage, crop rotation, and cultural practice on N balance based on N inputs and outputs and soil N sequestration rate under dryland cropping systems in the northern Great Plains, USA. Tillage systems were no-tillage (NT) and conventional tillage (CT) and crop rotations were continuous spring wheat (Triticum aestivum L.) (CW), spring wheat–pea (Pisum sativum L.) (W–P), spring wheat–barley (Hordeum vulgaris L.) hay–pea (W–B–P), and spring wheat–barley hay–corn (Zea mays L.)–pea (W–B–C–P). Cultural practices were traditional (conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height) and improved (variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height). Total N input due to N fertilization, pea N fixation, atmospheric N deposition, crop seed N, and nonsymbiotic N fixation was greater with W–B–C–P than CW, regardless of tillage and cultural practices. Total N output due to aboveground biomass N removal and N losses due to denitrification, volatilization, plant senescence, N leaching, gaseous N (NO_x) emissions, and surface runoff were not different among treatments. Nitrogen sequestration rate at 0–20 cm from 2004 to 2011 varied from 29 kg N ha^?1 year^?1 in CT with W–P to 89 kg N ha^?1 year^?1 in NT with W–P. Nitrogen balance varied from ? 39 kg N ha^?1 year^?1 in NT with CW and the improved practice to 41 kg N ha^?1 year^?1 in CT with W–P and the traditional practice. Because of legume N fixation and increased soil N sequestration rate, diversified crop rotations reduced external N inputs and increased aboveground biomass N removal, N flow, and N balance compared with monocropping, especially in the CT system. As a result, diversified legume–nonlegume crop rotation not only reduced the cost of N fertilization by reducing N fertilization rate, but also can be productive by increasing N uptake and N surplus and environmentally sustainable by reducing N losses compared with nonlegume monocropping, regardless of cultural practices in dryland agroecosystems.     

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.     

Nitrogen balance in a stockless organic cropping system with different strategies for internal N cycling via residual biomass

A major future challenge in agriculture is to reduce the use of new reactive nitrogen (N) while maintaining or increasing productivity without causing a negative N balance in cropping systems. We investigated if strategic management of internal biomass N resources (green manure ley, crop residues and cover crops) within an organic crop rotation of six main crops, could maintain the N balance. Two years of measurements in the field experiment in southern Sweden were used to compare three biomass management strategies: anaerobic digestion of ensiled biomass and application of the digestate to the non-legume crops (AD), biomass redistribution as silage to non-legume crops (BR), and leaving the biomass in situ (IS). Neither aboveground crop N content from soil, nor the proportion of N derived from N₂ fixation in legumes were influenced by biomass management treatment. On the other hand, the allocation of N-rich silage and digestate to non-legume crops resulted in higher N₂ fixation in AD and BR (57 and 58 kg ha^?1 year^?1), compared to IS (33 kg ha^?1 year^?1) in the second study year. The N balance ranged between ??9.9 and 24 kg N ha^?1, with more positive budgets in AD and BR than in IS. The storage of biomass for reallocation in spring led to an increasing accumulation of N in the BR and AD systems from one year to another. These strategies also provide an opportunity to supply the crop with the N when most needed, thereby potentially decreasing the risk of N losses during winter.     

Nitrate leaching from organic and conventional arable crop farms in the Seine Basin (France)

In the Seine Basin, characterised by intensive arable crops, most of the surface and groundwater is contaminated by nitrate (NO₃ ^?). The goal of this study is to investigate nitrogen leaching on commercial arable crop farms in five organic and three conventional systems. In 2012–2013, a total of 37 fields are studied on eight arable crop rotations, for three different soil and climate conditions. Our results show a gradient of soil solution concentrations in function of crops, lower for alfalfa (mean 2.8 mg NO₃-N l^?1) and higher for crops fertilised after legumes (15 mg NO₃-N l^?1). Catch crops decrease nitrate soil solution concentrations, below 10 mg NO₃-N l^?1. For a full rotation, the estimated mean concentrations is lower for organic farming, 12 ± 5 mg NO₃-N l^?1 than for conventional farming 24 ± 11 mg NO₃-N l^?1, with however a large range of variability. Overall, organic farming shows lower leaching rates (14–50 kg NO₃-N ha^?1) than conventional farms (32–77 kg NO₃-N ha^?1). Taking into account the slightly lower productivity of organic systems, we show that yield-scaled leaching values are also lower for organic (0.2 ± 0.1 kg N kg^?1 N year^?1) than for conventional systems (0.3 ± 0.1 kg N kg^?1 N year^?1). Overall, we show that organic farming systems have lower impact than conventional farming on N leaching, although there is still room for progress in both systems in commercial farms.     

Corn and soybean’s season-long in-situ nitrogen mineralization in drained and undrained soils

Many factors influence nitrogen (N) mineralization in agricultural soils. Our objective was to quantify cumulative (season-long) net N mineralization in corn (Zea mays L.) and soybean [Glycine max (L.) Merr] in a corn-soybean rotation under different N and soil drainage management (drained and undrained) in poorly-drained soils. In-situ incubations were conducted over two growing seasons using a sequential core-sampling technique to measure net N mineralization. Differential drainage was imposed three-years before this study, in which time, the soil lost 2.2 Mg C ha^?1 year^?1 and 0.14 Mg N ha^?1 year^?1 due to tile-drainage. Overall greater total soil organic carbon (TOC) and total soil nitrogen (TN) in the undrained soil resulted in 2.7 times greater net N mineralization compared to the drained soil in the unfertilized control (0N), but the effect of drainage was inconsistent across years with N fertilization. Across all variables, soils mineralized 2.89% of TN in soybean residue and 0.94% of TN in corn residue. Nitrogen fertilization increased mineralization rate, as high as 9.6 kg N ha^?1 day^?1, compared to <2.2 kg N ha^?1 day^?1 for 0N. Overall, net N mineralization was 3.4 times greater with N fertilizer than the 0N, but fertilization made mineralization more variable. The impact of fertilization on boosting mineralization under differential soil drainage needs further refinement if we are to improve decision-making tools for N application based on soil mineralization predictions.     

Effect of green manure and supplemental fertility amendments on selected soil quality parameters in an organic potato rotation in Eastern Canada

The effects of green manure, crop sequence and off-farm composts on selected soil quality parameters were assessed in a three-year organic potato (Solanum tuberosum L.) rotation in Eastern Canada. Three crop sequences varying in preceding green manure [red clover (RCl) + RCl, and beans/buckwheat or carrots + oats/peas/vetch mixture (OPV)] as main plots and four fertility treatments applied in the potato phase only [control; inorganic fertilizer; municipal solid waste compost (MSW); composted paper mill biosolid (PMB)] as subplots were compared. In 2008 and 2010, changes in selected soil quality parameters (0–15 cm) were assessed prior to planting of potatoes and at potato tuber initiation stage. Potentially mineralizable nitrogen (N) and the acid phosphatase enzyme activity average values across years were greater following RCl (1.51 abs and 622 kg ha^?1) compared with OPV (1.32 abs and 414 kg ha^?1) at potato planting. Soil NO₃–N average value was greater following RCl compared with OPV (63 vs. 52 kg ha^?1) at tuber initiation. For the other measured parameters, OPV and RCl were similar. The soil organic carbon (C) and particulate organic matter-C were greater under PMB and MSW (31.1 and 7.57 kg ha^?1) compared with fertilizer treatment (27.9 and 6.05 kg ha^?1). The microbial biomass C and microbial biomass quotient were greater under MSW (216 kg ha^?1 and 0.73 %) than PMB and fertilizer (147 kg ha^?1 and 0.50 %) across crop rotations. Annual legume green manures and off-farm composts can be used to satisfy potato N requirement and maintains soil quality in organic potato rotations.     

Nitrogen management in organic farming: comparison of crop rotation residual effects on yields,N leaching and soil conditions

After 3 years of different crop rotations in an organic farming experiment on a sandy soil in northwest Germany, spring triticale was cultivated on all plots in the fourth year to investigate residual effects on yield, nitrogen (N) leaching and nutrient status in the soil. Previous crop rotations differed in the way N was supplied, either by farmyard manure (FYM, 100 and 200 kg N ha⁻¹ year⁻¹) or by arable legumes like grass-red clover and field beans, or as a control with no N. Other crops in the rotations were maize, winter triticale and spring barley. Additional plots had a 3-year grass-clover ley, that was ploughed-in for spring triticale in the fourth year. Yields of spring triticale were moderate and largest for ploughed-in grassland leys and grass-red clover and plots that had previously received farmyard manure. The former crop rotation, including grassland break-up, had a significant effect on most yield and environmental parameters like residual soil mineral nitrogen (SMN) and N leaching and on the level of available K in the soil. The single crop harvested in the year before spring triticale had a significant effect on yield parameters of spring triticale, less so on SMN and N leaching in the fourth year and no effect on available nutrients (P, K, Mg) and pH in the soil. We conclude that the effects of arable legumes were rather short lived while ploughing of 3-year grassland leys had a profound influence on mineralization processes and subsequently on yield and N losses.     

Quantification of nitrogen inputs from biological nitrogen fixation to whole farm nitrogen budgets of two dairy farms in Atlantic Canada

Legume biological N fixation (BNF) is a large source of uncertainty in farm N budgets. This study sought to quantify the BNF-N input to two whole farm nitrogen budgets and establish a simple and accurate method for incorporating BNF values as inputs in whole farm N budgets. Nitrogen inputs and outputs as well as flows of N between animal and crop production components were determined for a dairy farm in New Brunswick (NB) and Prince Edward Island (PE) over a two year period. The ¹⁵N natural abundance method was used to determine the %N derived from the atmosphere (%Ndfa) through BNF at both sites. Red clover (Trifolium pratense) at the PE site derived 77 % of its N from BNF and alfalfa (Medicago sativa) collected at both the PE and NB farms derived 72 % of its N from BNF. Total BNF-N present in legume biomass from mixed forage fields measured with the ¹⁵N natural abundance method ranged from 39 to 116 kg N ha^?1 year^?1. A legume dry matter conversion model adjusted with %Ndfa and %N of red clover and alfalfa samples from both farm sites was selected to estimate BNF-N inputs from mixed forage fields on the farms. Averaged across the entire cropland area at each farm site, the BNF-N inputs ranged from 27 to 52 kg N ha^?1 year^?1. The farmgate BNF-N inputs are low in comparison to other studies, possibly due to low legume contents in forage fields. BNF accounted for 18–29 % of farmgate N inputs at the farms. Surpluses of N found at both farm sites ranged from 98 to 135 kg N ha^?1 year^?1, typical to the whole farm N budgets of similar dairy farms.     

Soil N mineralization in a dairy production system with grass and forage crops

This paper describes the dynamics of soil N mineralization in the experimental intensive dairy farming system ‘De Marke’ on a dry sandy soil in the Netherlands. We hypothesized that knowledge of the effects of crop rotation on soil N mineralization and of the spatial and temporal variability of soil N mineralization in a farming system can be used to better synchronize N application with crop N requirements, and hence to increase the recovery of applied N and to reduce N losses. Soil N mineralization was recorded continuously in the soil layer 0–0.30 m, from 1992 to 2005, using a sequential in situ coring technique on six observation plots, of which two were located in permanent grassland and four in crop rotations with a 3 year grassland phase and an arable phase of 3 or 5 years, dominated by maize. Average annual soil N mineralization was highest under permanent grassland: 381 kg ha^?1 and lowest under ≥3rd years arable crops: 184 kg ha^?1. In temporary grassland, soil N mineralization increased in the order: 1st year, 2nd year, 3rd year grassland and in arable crops after grassland mineralization decreased in the order: 1st year, 2nd year, ≥3rd years. Total mineral N input, i.e. the sum of N mineralization and mineral N supply to soil, exceeded crop N requirements in 1st year maize and was lower than the requirements in 1st year temporary grassland. N mineralization in winter, outside the growing season, was 77 kg ha^?1 in maize and 60 kg ha^?1 in grassland. This points at the importance of a suitable catch crop to reduce the susceptibility to N leaching. Temporal and spatial variability of soil N mineralization was high and could not be related to known field conditions. This limits the extent to which N fertilization can be adjusted to soil N mineralization. Variability increased with the magnitude of soil N mineralization. Hence, situations with high soil N mineralization may be associated with high risks for N losses and to reduce these risks a strong build-up of soil organic N should be avoided. This might be achieved, for instance, by fermenting slurry before application on farmland to enhance the fraction mineral N in slurry at the expense of organic N.     

Soil mineral nitrogen availability predicted by herbage yield and disease resistance in red clover (<Emphasis Type="Italic">Trifolium pratense</Emphasis>) cropping

Nitrogen (N) is the most limiting nutrient in crop production. Legumes such as red clover can provide N through biofixation, but securing nitrogen in soil for subsequent crop production must also be considered. Variety selection and management in red clover cropping can influence soil mineral nitrogen (SMN) availability. A field trial to investigate this was conducted with six varieties, under one and two cut management, over 2 years. Dry matter (DM) and N yield, Sclerotinia resistance and SMN availability were assessed. Low DM and N yields (1.6–2.4 t DM ha^?1 and 54–83 kg N ha^?1) in the first year of cultivation allowed ~?40 kg N ha^?1 to become available, but high DM and N yields (10.2–14.6 t DM ha^?1 and 405–544 kg N ha^?1) allowed ~?20 kg N ha^?1 to become available. Wetter weather in 2015 caused significantly more SMN losses than 2016 (20 kg N ha^?1 in 2015 and 5 kg N ha^?1 in 2016). The varieties Amos, Maro and Milvus lost significantly more SMN in the winter period, which may have been caused by more severe infection of Sclerotinia (these varieties were 50–80% more severely infected other varieties). Varietal effect was non-significant for winter losses in 2016, where no significant varietal differences in Sclerotinia infection were observed. 1 cut made ~?41 kg N ha^?1 available in the growing season of 2015, whilst 2 cut made significantly less (37 kg N ha^?1). Cutting was non-significant in 2016 but 1 cut was less susceptible to losses in the winter period. Cutting in 2015 did not significantly affect herbage DM and N yields in the first or second cut of 2016.     

Crop yields and soil organic carbon fractions as influenced by straw incorporation in a rice–wheat cropping system in southeastern China

In agro-ecosystems, the relationship between soil fertility and crop yield is mediated by manure application. In this study, an 8-year field experiment was performed with four fertilizer treatments (NPK, NPKM₁, NPKM₂, and NPKM₃), where NPK refers to chemical fertilizer and M₁, M₂, and M₃ refer to manure application rates of 15, 30, and 45 Mg ha^?1 year^?1, respectively. The results showed that the NPKM (NPKM₁, NPKM₂, and NPKM₃) treatments produced greater and more stable yields (4.95–5.45 Mg ha^?1 and 0.59–0.75) than the NPK treatment (4.01 Mg ha^?1 and 0.50). Crop yields under the NPKM treatments showed two trends, with a rate of decrease of 0.48–0.83 Mg ha^?1 year^?1 during the first 4 years and a rate of increase of 0.10–0.25 Mg ha^?1 year^?1 during the last 4 years. The soil organic carbon (SOC) significantly increased under all treatments. The estimated annual SOC decomposition rate was 0.35 Mg ha^?1 year^?1 and the equilibrium SOC level was 6.22 Mg ha^?1. Soil total nitrogen (N), available N, total phosphorus (P) and available P under the NPKM treatments increased by 0.15–0.26, 15–33, 0.17–0.66 and 45–159 g kg^?1, respectively, compared with the NPK treatment. Manure application mainly influenced crop yield by affecting the soil TN, available N, and available P, which accounted for up to 64% of the crop yield variation. Taken together, applying manure can determine or at least improve the effects of soil fertility on crop yield in acidic soils in South China.     

Soil surface N balances and soil N content in a clay-loam soil under Irish dairy production systems

This study evaluated the effect of a dairy system involving grazing over the winter on a soil surface N balance (SSB) and soluble N content in a clay loam soil in comparison with early spring calving systems. The SSBs were calculated for each paddock within three dairy systems for 2 years. Inputs included N entering the soil in fertilizer, slurry, excreta, atmospheric deposition and biological N fixation. Outputs consisted of N leaving the soil in harvested and grazed herbage. Nitrogen surplus was calculated as a difference between N inputs and outputs. Soluble N was assessed in soil extracts at three depths to 0.9 m. The management of the systems resulted in N surplus from 113 to 161 kg N ha^?1 year^?1 and N use efficiency of the soil component from 63 to 72 % without significant variation between the systems. The dairy system had no effect on soil N content as its variation was likely buffered by inherent soil properties (heavy texture, high C, pH) and the presence of shallow groundwater. The biochemical anaerobic reduction processes (i.e. denitrification) likely ensured soil oxidised N consistently low (<20 kg ha^?1). Consequently, the system involving grazing over the winter on these soils did not create an additional environmental pressure via N losses to groundwater and N₂O emissions compared with early spring calving systems. The size of soil inorganic N pools was mainly controlled by the hydrological factors and soil temperature, which are the most important factors controlling microbial activity, biochemical processes and leaching.     

Nutrient flows and balances in urban and peri-urban agroecosystems of Kano, Nigeria

Nutrient balances are useful indicators to assess the sustainability of farming systems. This study study investigates inflow and outflow of major nutrients in urban and periurban production systems in Kano, Nigeria. To this end, 16 households representing three different urban and peri-urban (UPA) farming systems were studied using the MONQI toolbox (formerly known as NUTMON) to calculate nutrient flows and economic performances. The farm nitrogen (N) balance was positive at 56.6, 67.4 and 56.4 kg farm^?1 year^?1 for commercial garden and crop-livestock (cGCL), commercial gardening and semi-commercial livestock (cGscL) and commercial livestock subsistence field cropping (cLsC) farm types, respectively. The same trend was observed for phosphorus (P) and potassium (K) in all farm types except an annual negative K balance of 16 kg farm^?1 in cGCL. Across the different activities within the farms, land uses had positive N (359, 387 and 563 kg N ha^?1 year^?1) and P (74, 219 and 411 kg P ha^?1 year^?1) balances for all farm types, but again a negative K balance in cGCL with an average loss of 533 kg K ha^?1 year^?1. Partial nutrient balances in livestock production indicated a positive balance for all nutrients across the farms types but were slightly negative for P in cLsC. Commercial livestock keeping (cLsC) was economically more profitable than the other farm types with an average annual gross margin (GM) and net cash flow (NCF) of $9,033 and $935. Cropping activities within cGCL and cGscL had GMs of $1,059 and $194 and NCFs of $757 and $206, respectively, but livestock activities in both farm types incurred financial losses. Potassium inputs were limited under vegetable and crop production of cGCL, threatening long-term K nutrient availability in this system. Overall, the results indicated large annual surpluses of N and P in urban and peri-urban vegetable and crop production systems which pose a potential threat when lost to the environment. Appropriate policies should aim at promoting sustainable production through efficient nutrient management in the Kano UPA sector.     

Fertigation combined with catch crop maximize vegetable yield and minimize N and P surplus

Excessive fertilization is a common agricultural practice that often results in high risk of nitrogen (N) and phosphorus (P) losses in vegetable production in China. To reduce these losses, it is crucial to control residual nutrient levels in the rootzone and maintain crop growth. A 3-year field experiment was therefore conducted to investigate the effects of optimal fertigation (OF), OF combined with summer catch crop (OF-SCC; sweet corn with residue incorporation after harvest) or wheat straw application (OF-WSA; soil amended with wheat straw before cucumber seedling transplanting) on soil nutrients, soil residual N and P levels in the rootzone. The conventional management (flood irrigation with excessive fertilization and bare fallow during the summer period) served as control. The results showed that, although OF reduced irrigation amount, N input and P input by 49, 50 and 53%, respectively, it did not affect N and P uptake and fruit yields, and significantly reduced N and P surplus in the rootzone by 60 and 59%, respectively, when compared to the control. The SCC extracted 72–74 kg N ha^?1 year^?1 and 10–13 kg P ha^?1 year^?1 from soils. In addition, SCC and WSA increased soil soluble organic N in the rootzone but had little influence on N and P surplus. Generally, OF was efficient in reducing soil residual N and P, while SCC could temporarily retarded N leaching and improved nutrient recycling in the rootzone. Our results infer that OF combined with SCC is an efficient method for reducing soil N and P losses.     

Carbon and nutrient fluxes and balances in Nuba Mountains homegardens,Sudan

Management intensification has raised concerns about the sustainability of homegardens in the Nuba Mountains, Sudan. This study aimed at assessing the sustainability of these agroecosystems following the approach of carbon (C) and nutrient balances. Three traditional (low input) and three intensified (high input) homegardens were selected for monitoring of relevant input and output fluxes of C, nitrogen (N), phosphorus (P) and potassium (K). The fluxes comprised those related to management activities (soil amendments, irrigation, and biomass removal) as well as estimates of biological N₂ fixation, C fixation by photosynthesis, wet and dry deposition, gaseous emission, and leaching. Annual balances for C and nutrients amounted to ?21 kg C ha^?1, ?70 kg N ha^?1, 9 kg P ha^?1 and ?117 kg K ha^?1 in high input homegardens and to ?1,722 kg C ha^?1, ?167 kg N ha^?1, ?9 kg P ha^?1 and ?74 kg K ha^?1 in low input homegardens. Photosynthesis C was the main C input flux with averaged of 7,047 and 5,610 kg C ha^?1 a^?1 in high and low input systems, respectively. Biological N₂ fixation (17 kg N ha^?1 a^?1) was relevant only in low input systems. In both systems, the annual input of 77 kg K ha^?1 through dust was highly significant and annual gaseous C losses of about 5,900 kg C ha^?1 were the main C loss. In both garden types, the removal of biomass accounted for more than half of total nutrient exports of which one-third resulted from weeding and removal of plant residues and two-third from harvest. The observed negative nutrient balances may lead to a long-term decline of crop yields. Among other measures the reuse of C and nutrients in biomass removals during the cleaning of homegardens may allow to partially close C and nutrient cycles.     

Nutrient transfers by leaching in a no-tillage system through soil treated with repeated pig slurry applications

Repeated pig slurry applications cause accumulation and leaching of soil nutrients and, subsequently, groundwater contamination. The purpose of this study was to evaluate ammonium (NH₄ ⁺–N), nitrate (NO₃ ^?–N), phosphorus (P) and potassium (K) leaching in a sandy soil with a 5-year history of repeated pig slurry applications. The study was carried out in the experimental field of the Universidade Federal de Santa Maria (UFSM) (Federal University of Santa Maria), Santa Maria, Rio Grande do Sul, in the South of Brazil, from 2002 to 2007, in no-tillage system in a Typic Hapludalf soil. Slurry was applied at doses of 0, 20, 40 and 80 m³ ha^?1, which over the 5 years amounted to the addition of 594, 1,188 and 2,376 kg N ha^?1; 508, 1,016 and 2,032 kg P ha^?1 and 216, 432 and 864 kg K ha^?1, respectively. Leachate solutions were collected throughout the period, prepared and then subjected to analysis of NH₄ ⁺–N, NO₃ ^?–N, P and K available in the solution. Repeated applications of pig slurry in a no-tillage system in sandy soil led to the transfer of elements through the leachate solution according to the sequence: nitrate > potassium > ammonium > phosphorus. The transfers of these elements were positively related to the increased volume of leachate solution over the years in addition to the nutrient amounts added by the pig slurry applied over the 60-month period.     

Assessing agronomic and environmental implications of different N fertilisation strategies in subtropical grain cropping systems on Oxisols

A multi-season ¹⁵N tracer recovery experiment was conducted on an Oxisol cropped with wheat, maize and sorghum to compare crop N recoveries of different fertilisation strategies and determine the main pathways of N losses that limit N recovery in these agroecosystems. In the wheat and maize seasons, ¹⁵N-labelled fertiliser was applied as conventional urea (CONV) and urea coated with a nitrification inhibitor (DMPP). In sorghum, the fate of ¹⁵N-labelled urea was monitored in this crop following a legume ley pasture (L70) or a grass ley pasture (G100). The fertiliser N applied to sorghum in the legume-cereal rotation was reduced (70 kg N ha^?1) compared to the grass-cereal (100 kg N ha^?1) to assess the availability of the N residual from the legume ley pasture. Average crop N recoveries were 73 % (CONV) and 77 % (DMPP) in wheat and 50 % (CONV) and 51 % (DMPP) in maize, while in sorghum were 71 % (L70) and 53 % (G100). Data gathered in this study indicate that the intrinsic physical and chemical conditions of Oxisols can be extremely effective in limiting N losses via deep leaching or denitrification. Elevated crop ¹⁵N recoveries can be therefore obtained in subtropical Oxisols using conventional urea while in these agroecosystems DMPP urea has no significant scope to increase fertiliser N recovery in the crop. Overall, introducing a legume phase to limit the fertiliser N requirements of the following cereal crop proved to be the most effective strategy to reduce N losses and increase fertiliser N recovery.     

Growth,grain yield and nitrogen use efficiency of Mediterranean wheat in soils amended with municipal sewage sludge

The application of sewage sludge (SS) to agricultural land can improve soil fertility and physical properties, and enhance crop production. This field study was conducted for two consecutive growing seasons to investigate the influence of SS application on winter wheat growth, grain yield, N accumulation, translocation and use, and on trace elements concentrations in soil and wheat plants under Mediterranean conditions. Treatments consisted of three rates of SS, i.e. 20, 40, and 60 Mg dry weight ha^?1 year^?1, one rate of inorganic fertilizer (IF, 120 kg N ha^?1 year^?1 plus 80 kg P₂O₅ ha^?1 year^?1), and an unamended control. The application of SS resulted in tall plants with high early dry matter and N accumulation similar to or significantly higher than those obtained with IF. The lowest SS application rate resulted in grain yield similar to that obtained with IF. Nitrogen use efficiency (NUE) in SS treatments was mainly determined by uptake efficiency, which decreased with increasing SS application rate. Values of NUE and biomass production efficiency with the lowest SS rate were similar to those obtained with IF. SS application resulted in increased concentrations of total and DTPA-extractable trace elements in the soil after the first year, but concentrations were much lower than the regulation limits. Concentrations of Cu, Mn and Zn in wheat plants did not exceed those obtained with IF. Overall, SS could be considered for use as a fertilizer in wheat production systems in the area, serving also as an alternative method of SS disposal.     

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.     

Differential retention of carbon, nitrogen and phosphorus in grassland soil profiles with long-term manure application

Liquid hog manure (LHM) is a valuable source of nutrients for farm production. Long-term experimental plots that had received LHM applications of 0, 50, and 100 m³ ha^?1 annually for 20 years were analyzed for total soil C, N and P storage. Applications increased total soil N and P by 1,200 kg N ha^?1 and 850 kg P ha^?1 at 100 m^?3 LHM year^?1, compared to the control treatment. However, C storage did not increase with LHM rates and was lower in the 50 m³ ha^?1 LHM treatment (86 Mg C ha^?1) than in the 0 or 100 m³ ha^?1 treatments (100 Mg C ha^?1). In addition to the limited quantities and high decomposability of the C supplied by LHM, it is hypothesized that LHM stimulated the mineralization of both native soil C and fresh root-derived material. This priming effect was particularly apparent in deeper soil horizons where the decomposability of native C may be limited by the supply of fresh C. This study indicates that while LHM can be a significant source of crop nutrients, it has limited capacity for maintaining or increasing soil C.