The influence of tillage on NO and N2O fluxes under spring and winter barley

Abstract. There is a lack of information about the influence of tillage and time of sowing on N₂O and NO emission in cereal production. Both factors influence crop growth and soil conditions and thereby can affect trace gas emissions from soils. We measured fluxes of NO and N₂O in a tillage experiment where grassland on clay loam soil was converted to arable by either direct drilling or ploughing to 30 cm depth. We made measurements in spring for 20 days after fertilizer application to spring-sown and to winter-sown barley. Both were the second barley crop after grass. Direct drilling enhanced N₂O emission primarily as a result of restricted gas diffusivity causing poor aeration after rainfall. Deep ploughing enhanced NO emission, because of the large air-filled porosity in the topsoil. NO and N₂O emissions were smaller from winter sown crops than from spring sown crops.   The three rates of N fertilizer application (40, 80 or 120 kg N ha^–1) did not produce the expected linear response in either soil available N concentrations or in NO and N₂O fluxes. We attributed this to the lack of rainfall in the ten-day period after fertilizer application and therefore very slow incorporation and movement of fertilizer into and through the soil.     

Nitrate leaching from organic farms and conventional farms following best practice

Abstract. This paper compares nitrate leaching losses from organic farms, which depended on legumes for their nitrogen inputs (66 site years) with those from conventional farms using fertilizers under similar cropping and climatic conditions (188 site years). The conventional farms were within Nitrate Sensitive Areas in England, but sites following special practices associated with that scheme were excluded. Nitrate losses during the organic ley phase (including the winter of ploughing out) were similar (45 kg N ha^–1) to those from conventional long-term grass receiving fertilizer N inputs of less than 200 kg N ha^–1 (44 kg N ha^–1) and from the grass phase of conventional ley-arable rotations (50 kg N ha^–1). Losses from conventional grass receiving higher N inputs were greater than from organic or less intensive grass. Nitrate losses following arable crops averaged 47 and 58 kg N ha^–1 for the organic and conventional systems respectively, with part of the difference being due to the greater proportion of non-cereal break crops in the latter. Thus under similar cropping, losses from organic systems are similar to or slightly smaller than those from conventional farms following best practice.     

The estimation of mineralization, immobilization and nitrification in nitrogen-15 field experiments using computer simulation

A combination of mathematical analysis and computer simulation, using parameters readily measured in a nitrogen-15 field experiment, is employed to determine rates of mineralization, immobilization and nitrification under a growing crop. The procedure also yields the proportion of crop nitrogen uptake occurring as ammonium and nitrate.
When applied to -results from grass lysimeters receiving 250 or 900 kg N ha^–1 a^–1 as ammonium nitrate, the analysis suggested that at 250 kgN ha^–1 a^–1 64–66% of crop nitrogen uptake was as ammonium; at 900 kg N ha^–1 a^–1 the figure was 43–49%. Nitrification at 250kgNha^–1 was only 13–19kgN ha^–1 over 160d while at 900 kg N ha^–1 between 191 and 232 kg N ha^–1 were nitrified.
The results suggested that the apparent inhibition of nitrification in grassland soils may simply reflect poor substrate competition by nitrifying bacteria. Finally, there was a suggestion that mineralization/immobilization was lower at the high fertilizer rate.     

Experimental assessment of runoff and soil erosion in an olive grove on a Vertic soil in southern Spain as affected by soil management

Abstract. Three different management systems were compared in an olive grove on a Vertic soil, near the city of Cordoba, Spain. Rainfall, runoff and soil loss were recorded from experimental plots of 6×12 m for three years. Results indicated that the no-tillage system, which was kept weed-free with herbicides, gave the largest soil loss (8.5 t ha⁻¹ yr⁻¹) and average annual runoff coefficient (21.5%), due to increased soil compaction, particularly outside the canopy projection area. A system that used a grass cover gave the lowest soil losses (1.2 t ha⁻¹ yr⁻¹) and average annual runoff coefficient (2.5%) due to the protective effects of the cover and increased soil aggregate stability. The third system, conventional tillage, gave intermediate results, with a soil loss of 4.0 t ha⁻¹ yr⁻¹ and an average runoff coefficient of 7.4%. The search for alternative soil management to conventional tillage should consider occasional light tillage to establish a grass cover that would keep both soil erosion and runoff losses to a minimum.     

Soil management for Alfisols in the semiarid tropics: erosion, enrichment ratios and runoff

Abstract. Continuous cultivation of soils of the semiarid tropics has led to significant land degradation. Soil erosion and nutrient loss caused by high runoff volumes have reduced crop yields and contributed to offsite damage. We compared a number of soil management practices (tillage, mulch and perennial/annual rotational based systems) for their potential to improve crop production and land resource protection in an Alfisol of the semiarid tropics of India. Runoff and soil erosion were monitored and surface soil and sediment were analysed for nitrogen and carbon to determine enrichment ratios. Amelioration of soils with organic additions (farmyard manure, rice straw) or rotating perennial pasture with annual crops increased soil carbon and nitrogen contents and reduced runoff, soil erosion and nutrient loss. Soil erosion totalled less than 7 t ha^–1, but enrichment ratios were often greater than 2 resulting in up to 27 kg N ha^–1 and 178 kg C ha^–1 being lost in sediment. Up to an extra 250 mm of water per year infiltrated the soil with organic additions and was available for crop water use or percolation to groundwater. The results show that there are good opportunities for reducing degradation and increasing productivity on farms.     

Laboratory studies of effects of lime on soluble Al, Ca, Mg and Mn in a pelostagnogley soil

The cation composition of solutions and leachates from small-diameter laboratory soil columns was examined over a 23-week period after the addition of lime (0, 3 and 6 t ha^–1) and/or nitrogen fertilizer (0 or 200 kg N ha^–1) to an acid soil (pH 4.2). Water was applied at regular intervals to the surface of the columns and 17 leachate samples collected. Initially, the pH of the leachate was high (6.6) in all treatments (including those without lime) but fell rapidly to approach a steady value of 3.8. Large losses of calcium occurred from all columns; the total equivalent amounts of lime lost ranged from 0.88 (no addition) to 2.38 (with added lime) t CaCO₃ ha^–1 High concentrations of aluminium (181–325 μM) were present in leachates from all treatments; the addition of 200 kg N ha^–1 increased the leaching of Al by 94%; addition of lime also increased the amounts of Al leached (by 52%).
The pH of the soil solution (separated by centrifugation) was influenced by treatment, especially in the top 0–40 mm of the column. Aluminium concentration was related to pH, but the form of the relationship differed amongst the treatments.     

Long-term changes in soil organic matter under conventional tillage and no-tillage systems in semiarid Morocco

Abstract. A no-tillage (NT) system was developed in semiarid Morocco to improve the soil fertility and stabilize yield through conservation of water. Results in two long-term trials (4 and 11 years) were able to show the effects of a no-tillage system in increasing total soil organic matter and total nitrogen. Over time, the quality of the NT soil surface was improved compared with that under conventional tillage (CT) with disc harrows. This effect was the result of an increase in soil organic carbon (SOC) and a slight decline in pH. However, over time, nitrogen decreased in both tillage practices, especially in the 0–25 mm layer (from 0.59 to 0.57 t ha⁻¹ and from 0.44 to 0.42 t ha⁻¹ under NT and CT, respectively). After 4 years of NT an extra 5.62 t ha⁻¹ of SOC was sequestered in the 0–25 mm layer, and after 11 years the SOC increased further to 7.21 t ha⁻¹.     

Nitrate leaching and adsorption in a Kenyan Nitisol

Abstract. ¹⁵N labelled NH₄NO₃ (fertilizer N) was applied at a rate of 50 kg N ha^–1 to an Ando-Humic Nitisol and two maize crops grown on it. About 20 months later, soil cores were taken to a depth of 2.5 m. Leached fertilizer N was found between 1.4 m and 1.8 m deep and was delayed relative to net drainage by between 4.2 and 4.9 pore volumes. Anion exchange capacity (AEC) increased ten-fold down the profile, up to 2.9 cmol_ckg^–1. The delay to fertilizer N leaching was predicted to be between 4.1 and 5.3 pore volumes when calculated from the AEC and from an equation relating delay due to AEC in laboratory columns of repacked soil obtained by Wong et al. (1990b). It was concluded that the nitrate leaching delay equation was also valid in undisturbed field profiles. Two concentration maxima for mineral N were found, which did not usually coincide with the fertilizer N and were thought to result from mineralization of soil organic matter and plant residues at the end of each season. The delay equation overestimated their leaching delay but the results were considered close enough to support the hypothesis for their formation.     

Effect of plot scale and an upslope phosphorus source on phosphorus loss in overland flow

Abstract. Phosphorus (P) in overland flow is mediated by soil P, added P, erosion, and hydrological processes and their interaction as affected by landscape position and length of flow. We investigated the effect of flow path length (1 to 10 m long plots) on P transport in overland flow with and without a localized dairy manure application (75 kg P ha^–1 added to the upslope end [0.5 m] of each plot) and simulated rainfall (7 cm h^–1), at two sites within an agricultural watershed in Pennsylvania, USA. Particulate loss in overland flow was c . 20% greater from manured than unmanured plots due to the less dense nature of manure than soil. Increased soil moisture at Site 2 contributed to a greater loss of P compared to Site 1, both with and without manure; with most occurring as particulate P (60 to 90% of total P). Further, the selective erosion of fine particulates (24 to 34% clay) and P loss increased with plot length. From a management perspective our results demonstrate that the forms and amounts of P loss are greatly influenced by flow path length and interactions among antecedent moisture, soil P, and texture.     

A review of farm-scale nutrient budgets for organic farms as a tool for management of soil fertility

Abstract. On organic farms, where the importation of materials to build/maintain soil fertility is restricted, it is important that a balance between inputs and outputs of nutrients is achieved to ensure both short-term productivity and long-term sustainability. This paper considers different approaches to nutrient budgeting on organic farms and evaluates the sources of bias in the measurements and/or estimates of the nutrient inputs and outputs. The paper collates 88 nutrient budgets compiled at the farm scale in nine temperate countries. All the nitrogen (N) budgets showed an N surplus (average 83.2 kg N ha^–1 yr^–1). The efficiency of N use, defined as outputs/inputs, was highest (0.9) and lowest (0.2) in arable and beef systems respectively. The phosphorus (P) and potassium (K) budgets showed both surpluses and deficits (average 3.6 kg P ha^–1 yr^–1, 14.2 kg K ha^–1 yr^–1) with horticultural systems showing large surpluses resulting from purchased manure. The estimation of N fixation and quantities of nutrients in purchased manures may introduce significant errors in nutrient budgets. Overall, the data illustrate the diversity of management systems in place on organic farms, and suggest that used together with soil analysis, nutrient budgets are a useful tool for improving the long-term sustainability of organic systems.     

Denitrification in drained and undrained arable clay soil

Emissions of nitrous oxide (N₂O) and nitrogen gas (N₂) from denitrification were measured using the acetylene inhibition method on drained and undrained clay soil during November 1980-June 1981. Drainage limited denitrification to about 65% of losses from undrained soil. Emissions from the undrained soil were in the range 1 to 12 g N ha^–1 h^–1 while those from the drained soil ranged from 0.5 to 6 g N ha^–1 h^–1 giving estimated total losses (N₂O + N₂) of 14 and 9 kgN ha^–1.
Drainage also changed the fraction of nitrous oxide in the total denitrification product. During December, emissions from the drained soil (1.8±0.6 gN ha^–1 h^–1) were composed entirely of nitrous oxide, but losses from the undrained soil (2.7 ± 1.1 g N ha^–1 h^–1) were almost entirely in the form of nitrogen gas (the fraction of N₂O in the total loss was 0.02). In February denitrification declined in colder conditions and the emission of nitrous oxide from drained soil declined relative to nitrogen gas so that the fraction of N₂O was 0.03 on both drainage treatments. The delayed onset of N₂O reduction in the drained soil was related to oxygen and nitrate concentrations. Fertilizer applications in the spring gave rise to maximum rates of emission (5–12g N ha^–1 h^–1) with the balance shifting towards nitrous oxide production, so that the fraction of N₂O was 0.2–0.8 in April and May.     

Agricultural nitrogen balance and water quality in the UK

Abstract. Nutrient balance calculations have been advocated as indicators of the risk of nitrate loss from agricultural land. To explore this concept, a spatially distributed UK agricultural nitrogen balance was derived using annually updated statistics. The mean UK N surplus for 1995 was 115 kg N ha^–1, made up of 51 kg ha^–1for arable land, 140 kg ha^–1 for agricultural grassland (excluding rough grazing) and an additional 14 kg N ha^–1for agricultural land from pig and poultry units. Nitrogen surpluses were greater in lowland grassland (mainly in western, wetter areas) than in arable areas. However nitrate concentrations in rivers were generally greater in arable areas. The relationship between N balance and nitrate leaching was very different for grassland and arable systems, and was also sensitive to climate, level of inputs and management practices. Nitrogen surplus was therefore weakly or even negatively correlated with river nitrate concentrations or loads. A positive correlation was found only where the comparison was restricted to grassland-dominated catchments. Nitrogen surplus calculations identified areas of very high livestock densities, which would be associated with increased risk of pollution. However their use in isolation as indicators of N leaching, or of progress towards mitigation, could be misleading especially if comparing areas differing in land use, climate or soil type.     

Phosphorus cycling in UK agriculture and implications for phosphorus loss from soil

Abstract. Phosphorus (P) use in UK agriculture is reviewed and a P balance sheet presented. The productive grassland and arable area has accumulated an average P surplus of c. 1000 kg ha^–1 over the last 65 years. Over the period 1935–1970, the annual P surplus more than doubled due to an increase in animal numbers and associated requirements for inorganic fertilizers and livestock feeds. Since 1970, surplus P has declined by c . 40% as crop yields and P offtake have continued to increase while fertilizer and manure P inputs have remained relatively constant. In 1993, P use efficiency (P imports/P exports) in UK agriculture was estimated at 25% leading to an average annual surplus of 15 kg P ha^–1 yr^–1, although the latter has since decreased slightly due to reduced fertilizer use. Intensification and specialization of agriculture has also increased the range in P surpluses that are likely between livestock and arable dominated systems. The largest P surpluses occur in the relatively limited areas of arable soils which receive manure from intensive pig and poultry units, whilst farms without manure inputs generate only small surpluses, or are in balance. The cumulative P surplus has led to a build-up of soil total and easily-exchangeable P, especially in areas receiving both fertilizers and manures. Fundamental differences in P use efficiency, surplus P accumulation and the potential for P loss to water, exist between arable and grassland farms and it is important to separate these, due to the marked regionalization of UK agriculture. More judicial use of feeds and fertilizers is required to further reduce the P surplus and minimize the long-term risk of water eutrophication.     

Optimizing farmyard manure utilization by varying the application time and tillage strategy

Abstract. Two field experiments were carried from 1999 to 2001 to assess the effectiveness of autumn, winter and spring application of straw-based farmyard manure (FYM). The soil was a sandy loam containing 106 g clay kg⁻¹ situated in the temperate coastal climate of Denmark. The FYM was applied manually to experimental plots at a target rate of 300 kg N ha⁻¹. The manure was incorporated by three initial tillage strategies (harrowing, rotavating or no-tillage) prior to ploughing. All combinations of tillage strategies were also carried out without manure application. Spring barley ( Hordeum vulgare L.) was grown, followed by ryegrass ( Lolium perenne L.). The results suggest that, as far as circumstances permit, FYM should be applied in spring to achieve the optimum use of nitrogen in the manure. Further, yield and nitrogen uptake did not benefit from harrowing or rotavating the manure before ploughing. When manure was not applied, soil tillage prior to ploughing did not significantly affect grain yield or nitrogen uptake.     

Soil physical quality of a Brazilian Oxisol under two tillage systems using the least limiting water range approach

Plant growth is directly affected by soil water, soil aeration, and soil resistance to root penetration. The least limiting water range (LLWR) is defined as the range in soil water content within which limitations to plant growth associated with water potential, aeration and soil resistance to root penetration are minimal. The LLWR has not been evaluated in tropical soils. Thus, the objective of the present study was to evaluate the LLWR in a Brazilian clay Oxisol (Typic Hapludox) cropped with maize (Zea mays L. cv. Cargil 701) under no-tillage and conventional tillage. Ninety-six undisturbed soil samples were obtained from maize rows and between rows and used to determine the water retention curve, the soil resistance curve and bulk density. The results demonstrated that LLWR was higher in conventional tillage than in no-tillage and was negatively correlated with bulk density for values above 1.02 g cm⁻³. The range of LLWR variation was 0–0.1184 cm³ cm⁻³ in both systems, with mean values of 0.0785 cm³ cm⁻³ for no-tillage and 0.0964 cm³ cm⁻³ for conventional tillage. Soil resistance to root penetration determined the lower limit of LLWR in 89% of the samples in no-tillage and in 46% of the samples in conventional tillage. Additional evaluations of LLWR are needed under different texture and management conditions in tropical soils.     

Nitrous oxide emissions after application of inorganic fertilizer and incorporation of green manure residues

Abstract. Emissions of N₂O were measured after application of NH₄NO₃ fertilizer and incorporation of winter wheat and rye green manures in two field experiments in southeast England. Incorporation of green manure alone resulted in temporary immobilization of soil N, small N₂O emissions and also low availability of N for the following crop. Emissions were increased after application of inorganic fertilizer, and were further increased from integrated management treatments whereby green manure residues were incorporated after fertilizer application. The highest emission was from the incorporated winter wheat green manure plus fertilizer treatment, with 1.5 kg N₂O-N ha⁻¹ (0.6% of N applied) being emitted over the first 55 days after incorporation. This high emission was attributed to the supply of C in the residues providing the energy for denitrification in the presence of large amounts of mineral N and the creation of anaerobic microsites during microbial respiration.     

Influence of long-term tillage, straw and N fertilizer on barley yield, plant-N uptake and soil-N balance

Long-term influence of N fertilizer, tillage and straw on crop production and soil properties are not well known in central Alberta. Field experiments were established in autumn 1979, on a Black Chernozemic soil and on a Gray Luvisolic soil in north-central Alberta to determine the long-term effect of tillage, straw and N fertilizer on yield and N uptake of barley (Hordeum vulgare L.). Fertilizer N was applied annually at 56 kg ha⁻¹. The 11 year averages of barley yields and N uptake under zero tillage were lower than under conventional tillage. Retention rather than removal of straw tended to reduce barley yield for the initial 6 years and 2 year at Site 1 and Site 2, respectively. A simple mathematical model of average annual plant N uptake and grain yield could account for most of the variation in the data observed at both sites (R² = 0.907; P < 0.01). Final values of soil N, calculated using a mass balance approach, agree closely with values measured at the end of the eleventh year. Conventional tillage and zero tillage, with addition of fertilizer N and retention of straw, were the only treatments with apparent but small net addition of N to soil at Site 1 (40 kg ha⁻¹ and 117 kg ha⁻¹, respectively). At Site 2, only the zero tillage treatment with addition of fertilizer and retention of straw gained soil N (29 kg ha⁻¹). In conclusion, soil ecosystems functioning in subhumid environments with slight to moderate heat limitations such as those in central Alberta can adapt, within a few years, to zero tillage practices with full retention of straw.     

Influence of the addition of organic residues on carbohydrate content and structural stability of some highland soils in Ethiopia

Abstract. When over exploited and coupled with climatic conditions, tropical soils are subject to increased erosion and a loss of soil organic matter. Countermeasures include the incorporation of organic materials such as crop and animal residues. We studied the effect of adding crop residues and manure to soil, at five sites in Ethiopia, on carbohydrate properties, aggregate stability and the C and N distribution within water-stable aggregates. The effects of organic amendments varied between sites. The largest content of carbohydrates was obtained in the control treatment at Holeta, Ginchi (90 kg ha^–1 mustard meal), Jimma (5 t ha^–1 cow dung + 9 t ha^–1 coffee husk), Awassa (forested soil), and Sirinka (soil alley-cropped with Leuceanae ). The aggregate stability of these soils was highly correlated with the OM content but not with carbohydrates. The smaller aggregates (<1.00 mm) accumulated more carbohydrates than the larger (>1.00 mm), thereby suggesting a protecting effect within the finer soil fractions. A protecting role played by humified OM components was also indicated by the C and N distribution as well as the C:N ratios which showed preferential accumulation in small rather than in large aggregates. The isotopic ¹³C-OC values of carbohydrate extracts were generally low, suggesting that OM was from plants with C3 photosynthetic pathways. Soil treatments with maize alone or combined with coffee husks at Jimma decreased the δ¹³C‰ values slightly, revealing that maize contributed a share of the labile OM. Despite the improvement in the soil OM content, neither the carbohydrate content nor the aggregate stability were increased to the level of the forested sites, suggesting that the additions of crop residues and manure were not alone sufficient to restore the soil physical quality.     

The effects of minimal tillage and contour cultivation on surface runoff, soil loss and crop yield in the long-term Woburn Erosion Reference Experiment on sandy soil at Woburn, England

Abstract. Over a 10-year period, runoff and soil erosion on the plots of the Woburn Erosion Reference Experiment were concentrated in periods with sparse vegetation cover: in winter after the late planting of cereals; in spring after the planting of beets; or when soils were bare after harvest. The mean event runoff of 1.32 mm from plots cultivated up-and-downslope was significantly greater ( P <0.05) than that from plots cultivated across-slope (0.82 mm). However, mean event soil loss was not significantly different between the two cultivation directions. No significant differences were found between minimal and standard cultivations. Mean event runoff from the across-slope/minimal tillage treatment combination (0.58 mm) was significantly less ( P <0.01) than from the up-and-downslope/minimal tillage (1.41 mm), up-and-downslope/standard tillage (1.24 mm), and across-slope/standard tillage (1.07 mm) treatment combinations. Runoff from the across-slope/standard treatment combination was significantly ( P <0.05) less than from the up-and-downslope/minimal tillage treatment. The across-slope/minimal tillage treatment combination had a significantly smaller ( P <0.05) event soil loss (67 kg ha⁻¹) than the up-and-downslope/standard tillage (278 kg ha⁻¹) and up-and-downslope/minimal tillage (245 kg ha⁻¹) combinations. Crop yields were significantly ( P <0.05) higher on across-slope plots in 1988, 1996 and 1997 than on up-and-downslope plots, and were also higher (but not significantly) on the across-slope plots in 7 of the 8 remaining years. Minimal cultivation decreased yield compared with standard cultivation in one year only. We recommend that across-slope cultivation combined with minimal tillage be investigated at field scale to assess its suitability for incorporation into UK farming systems.     

The effect of N placement on grass weeds and winter wheat responses in three tillage systems

Field studies were conducted for three seasons (1978–1979, 1979–1980 and 1981–1982) on a Palouse silt loam near Pullman, Washington, to compare the effects of broadcast and deep banding of nitrogen (N) fertilizer beneath winter wheat (Triticum aestivum L.) seed on N uptake and dry matter production of downy brome (Bromus tectorum L.) and jointed goatgrass (Aegilops cylindrica Host.), and on N uptake, dry matter production and grain yields of winter wheat. Three tillage systems were used: conventional tillage; shallow roto-tilling, or no-tillage prior to planting. Rates of N were 0, 65, 130 and 190 kg N ha⁻¹ as ammonium nitrate. Additional plots were maintained free of weeds at the 130 kg N ha⁻¹ rate. In 1983–1984, deep banding of the fertilizer between rows in a paired-row configuration was compared to surface-broadcast N fertilizer using N rates of 0, 45, 90 and 135 kg N ha⁻¹. There were no significant differences between broadcast and deep-band application of N on grass weed N uptake or dry matter production with mold-board plowed or no-tillage, but there was greater weed growth with surface-broadcast N with shallow roto-tilling. Wheat N uptake, growth and grain yields were consistently higher with band-applied N compared to broadcast N. The yield response to banding N was the same with or without the presence of grass weeds.