Yield and N uptake as affected by soil tillage and catch crop

Two field trials with spring barley (Hordeum vulgare L.) were conducted at two locations in Denmark in order to evaluate the effects of tillage and growth of a catch crop on yield parameters under temperate coastal climate conditions. Ploughing in autumn or spring in combination with perennial ryegrass (Lolium perenne L.) as a catch crop was evaluated on a coarse sand (Orthic Haplohumod) from 1987 to 1992 at three rates of N fertiliser application (60, 90 and 120 kg N ha⁻¹ year⁻¹). Rotovating and direct drilling were also included as additional tillage practices. The experiment was conducted on a 19-year-old field trial with continuous production of spring barley. Ploughing in autumn or spring in combination with stubble cultivation and a catch crop, in addition to minimum tillage, was evaluated in a newly established field trial on a sandy loam (Typic Agrudalf) from 1988 to 1992. Yield parameters and N concentrations in grain and straw were determined. On the coarse sand, N uptake in the grain in ploughed plots without a catch crop was significantly greater when spring ploughed as opposed to autumn ploughed, but grain and straw yields did not differ significantly. Grain yield, straw yield and total N uptake did not differ significantly between direct drilled and autumn ploughed plots, but the trend was for grain yield to be lower with direct drilling. After 19 years of catch crop use, yield parameters in ploughed plots were greater than in plots without catch crops. This was most pronounced in the autumn ploughed plots. Rotovating the catch crop in the spring decreased grain yield compared with underploughing the catch crop in autumn or spring. No significant interactions were found between tillage and N rates. On the sandy loam, grain as well as straw yield and total N uptake were not significantly affected by catch crop or time of ploughing. Grain yield was significantly lower with reduced tillage (stubble cultivation in autumn) than in all other treatments.     

Nitrate leaching from organic arable crop rotations: effects of location, manure and catch crop

Abstract. Nitrate leaching from crop rotations supporting organic grain production was investigated from 1997 to 2000 in a field experiment at three locations in Denmark on different soil types. Three experimental factors were included in the experiment in a factorial design: (1) proportion of N₂-fixing crops in the rotation (crop rotation), (2) catch crop (with and without), and (3) manure (with and without). Three, four-course rotations were compared, two at each location. The nitrate leaching was measured using ceramic suction cells. Leaching losses from the crop rotation with grass–clover green manure and without catch crops were 104, 54 and 35 kg N ha⁻¹ yr⁻¹ on the coarse sand, the loamy sand, and the sandy loam, respectively. There was no effect of manure application or time of ploughing-in the grass–clover green manure crop on the accumulated nitrate leaching from the entire rotation. Catch crops reduced nitrate leaching significantly, by 30–38%, on the sandy soils. At all locations catch crops reduced the annual averaged nitrate concentration to meet drinking water quality standards in the crop rotation with green manure. On the coarse sand there was a time lag between the onset of drainage and the start of N-uptake by the catch crop.     

Interactions between soil organic matter level and soil tillage in a growing crop: N mineralization and yield response

Four levels of soil organic matter (SOM) had been established on a coarse sandy loam after application of four combinations of mineral fertilizer, animal manure, straw incorporation and catch crops for 12 years. Soil tillage was carried out in a growing spring barley crop (Hordeum vulgare) to examine the potential for improving the synchrony between soil N mineralization and crop N demand. Tillage raised soil nitrate concentrations temporarily but did not influence barley dry matter (DM) yield. At maturity, both grain DM yield and N uptake were largest on soil with the highest OM level. The previous OM applications had a pronounced influence on crop development and N availability, but soil tillage did not significantly improve the synchrony between soil N mineralization and crop N demand.     

Characterization of soil physical properties and organic matter under long-term primary tillage in a humid climate

Chisel ploughing is considered to be a potential conservation tillage method to replace mouldboard ploughing for annual crops in the cool-humid climate of eastern Canada. To assess possible changes in some soil physical and biological properties due to differences in annual primary tillage, a study was conducted for 9 years in Prince Edward Island on a Tignish loam, a well-drained Podzoluvisol, to characterize several mouldboard and chisel ploughing systems (at 25 cm), under conditions of similar crop productivity. The influence of primary tillage on the degree of soil loosening, soil permeability, and both organic matter distribution throughout the soil profile and organic matter content in soil particle size fractions was determined. At the time of tillage, chisel ploughing provided a coarser soil macrostructure than mouldboard ploughing. Mouldboard ploughing increased soil loosening at the lower depth of the tillage zone compared to chisel ploughing. These transient differences between primary tillage treatments had little effect on overall soil profile permeability and hydraulic properties of the tilled/non-tilled interface at the 15–30 cm soil depth. Although soil microbial biomass, on a volume basis, was increased by 30% at the 0–10 cm soil depth under chisel ploughing, no differences were evident between tillage systems over the total tillage depth. Mouldboard ploughing increased total orgainc carbon by 43% at the 20–30 cm soil depth, and the carbon and nitrogen in the organic matter fraction ≤ 53 μm by 18–44% at the 10–30 cm soil depth, compared to chisel ploughing.     

Nitrate leaching from a shallow limestone soil growing a five course combinable crop rotation: the effects of crop husbandry and nitrogen fertilizer rate on losses from the second complete rotation

Abstract. The field experiment tested the effects of three management systems on nitrate leaching losses from a five crop rotation on the Lincolnshire Limestone in Eastern England. The Standard system was similar to farming practice in the area. The Protective system integrated individual practices which were expected to decrease nitrate losses (e.g. cover crops, cultivation delay in autumn and reduced intensity, manipulation of drilling dates and, during the first few years of the first rotation, straw incorporation). The Intermediate system was a compromise between the two extremes. All crops were grown at full and half recommended nitrogen rates. This paper reports data from the second full rotation (years 6–10), thus enabling the medium-term effects of continued management practices to be investigated. Average annual nitrogen leaching losses at 49, 35 and 25 kg N ha^–1 for Standard, Intermediate and Protective systems, respectively, were significantly different. The respective flow-weighted average NO₃ concentrations were 167, 131 and 96 mg l^–1. Thus, adopting nitrate retentive practices through the rotation was able to substantially decrease losses. The Protective system was as effective as in the first full rotation, demonstrating that 10 years of such practices had not failed in the medium-term. However, continued minimal cultivation caused serious problems of weed build-up. The cost of weed control and yield loss caused by grass weeds made cereal production uneconomic in some years. Thus, rules for nitrate leaching control need to be tempered with practical and agronomic considerations. Also, few (if any) management techniques tested guaranteed that nitrate losses would be small in all years, as the interaction with winter weather, particularly rainfall, was of vital importance.     

Growth,radiation use efficiency and grain yield of wheat as influenced by nitrogen,tillage, and crop residue management

Abstract

Soil organic carbon (SOC) sequestration is one of the major agronomic measures to mitigate green house gas emission, enhance food security, and improve agriculture sustainability. The study, therefore, aimed to evaluate crop growth (CG) and radiation use efficiency in spring wheat (Triticum aestivum L.) treated soil with residue type (RT), that is, cowpea (Vigna unguiculata) as legume (LR), maize (Zea mays L.) as cereal (CR) and no residue (NR) treatment applied (5 t ha^?1) on dry matter basis. The CR was subsequently incorporated with tillage depths (TD), that is, deep (DT?=?35?cm) and shallow (ST?=?15?cm) as main plot treatments. The N was applied in two splits starting from 0 to 160?kg ha^?1 as sub plot treatments. Experiment was conducted in two CG seasons 2009–11 at Agronomy Research Farm, the University of Agriculture Peshawar, Pakistan. Results showed the highest CG and RUE with LR incorporated than CR and/or NR with DT. Increasing N-rate resulted an increase in CG, RUE and biomass of wheat. Residue of LR or CR deeply incorporate into the soil has resulted healthy traits (i.e., tillers- and spikes number), which resulted higher biomass. Nitrogen applied 120?kg ha^?1 resulted in higher CG, RUE and grain yield for treatment LR, followed by CR and the lowest for the NR. Crop of second year showed higher grain yield, which was due to healthy traits including better CG and RUE. The study suggests that CR of LR or CR nature incorporated deep into the soil can optimize crop N-fertilizer demand for optimum production, which protects environment from the excessive use of N application.     

Rotation and tillage effects on available soil water for winter wheat in a semi-arid environment

The recent adoption of conservation farming systems in the semi-arid Canadian prairies opens up the possibility of replacing the traditional fallow period with non-cereal crops (oilseeds, legumes). However, information on changes to soil water regimes by inclusion of these crops, especially in combination with zero tillage, is sparse. A study was initiated in 1984 on a sandy clay loam soil at Lethbridge, Alberta, to investigate the performance of winter wheat (Triticum aestivum L.) under conventional, minimum and zero tillage in monoculture and in 2-year rotations with fallow, canola (Brassica campestris L.) or lentils (Lens culinaris Medic.)/flax (Linum usitatissimum L.). Conventional tillage in the Lethbridge region is shallow cultivation (10 cm) with a wide-blade (sweep) cultivator. Continuous cropping greatly depleted soil water reserves, resulting in some crop failures. Averaged over 10 years, available water for establishment of winter wheat in fall was least after canola (45 mm), followed by continuous winter wheat (59 mm), lentils/flax (74 mm) and fallow (137 mm). In this semi-arid region, the effect of rotation on soil water was much greater than that of tillage. Zero tillage had relatively little impact on available water to 1.5 m depth. However, once the experiment had been established for 6–7 years, available water in the 0–15 cm depth under winter wheat in spring was greatest under zero tillage. Precipitation storage efficiency during the fallow year was generally unaffected by tillage system.     

Tillage and straw management for modifying physical properties of a subarctic soil

Conservation tillage practices are intended to minimize soil erosion. Yet little is known concerning changes in physical properties of subarctic soils subject to tillage practices. This study ascertained whether physical properties of a newly cleared subarctic soil are altered after 7 years of continuous barley (Hordeum vulgare L.) using different tillage and straw management strategies. Tillage and straw treatments were established in 1983 near Delta Junction, Alaska, and consisted of conventional fall and spring disk, fall chisel plow, spring disk, and no-tillage. Tillage plots were split by straw management practices, which included straw and stubble, stubble only, and no straw or stubble. Soil samples were collected from the upper 0.15 m of the profile in the spring of 1990 to assess water content, bulk density, saturated hydraulic conductivity, dry aggregate and mechanical stability, penetration resistance, water retention, and particle size distribution. Percent non-erodible aggregates, mechanical stability, and penetration resistance were greater for no-tillage compared to conventional tillage, chisel plow, and spring disk. No-tillage soils were also typically wetter, denser, and had a greater hydraulic conductivity. The spring disk treatment was least susceptible to erosion and also conserved soil water compared with chisel plow. Straw maintained on the surface conserved water and promoted soil stability.     

Total and labile soil organic nitrogen as influenced by crop rotations and tillage in Canadian prairie soils

Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha^–1year^–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha^–1year^–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha^–1 year^–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha^–1year^–1 to 28 kg N ha^–1year^–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha^–1year^–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha^–1year^–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.     

Soil organic matter quality as influenced by tillage,lime, and phosphorus

In Eastern Canada, cereal yields are often restricted by soil acidity and low fertility. Continuous cereal production can also lead to soil structural degradation. The addition of lime and fertilizers and the adoption of conversation tillage practices are proposed solutions which may have a positive impact on soil quality. The objective of the present work was to assess the impact of 3 years of different tillage practices and P additions, and of a single lime addition on organic C and total N, microbial biomass C, and on N mineralization at the surface layer (0–7.5 cm) of a Courval sandy clay loam (Humic Gleysol). The easily mineralizable N, total amount of N mineralized in 22.1 weeks, the rate of N mineralization, and microbial biomass C were significantly greater in the minimum tillage than in the moldboard plow treatment. Chisel plow treatment showed intermediate values. The ratios of potentially mineralizable N and of easily mineralizable to total soil N were also significantly larger under minimum tillage and chisel plowing than under moldboard plowing. The lime and P treatments had no significant effect on the measured soil quality parameters. The total amount of N mineralized per unit of biomass C decreased as the tillage intensity increased, suggesting a decrease in the efficiency of the biomass in transforming organic N into potentially plant-available forms and thus a loss in soil organic matter quality. The results of this study indicate that conservation tillage practices such as rototilling and chisel plowing are efficient ways of maintaining soil organic matter quality when old pastures are brought back into cultivation.     

Changes in N leaching and crop production as a result of measures to reduce N losses to water in a 6‐yr crop rotation

The effects of various measures introduced to increase nitrogen (N)‐use efficiency and reduce N losses to water in a 6‐yr crop rotation (winter wheat, spring barley, green manure, winter wheat, spring barley, spring oilseed rape) were examined with respect to N leaching, soil mineral N (SMN) accumulation and grain yield. An N‐use efficient system (NUE) with delayed tillage until late autumn and spring, direct drilling of winter wheat, earlier sowing of winter and spring crops and use of a catch crop in winter wheat was compared with a conventional system (CON) in a field experiment with six separately tile‐drained plots in south‐western Sweden during the period 1999–2011 (two crop rotation cycles). Total leaching of NO₃‐N from the NUE system was significantly 46 and 33% lower than in the CON system during the first and second crop rotation cycle, respectively, with the most pronounced differences apparently related to management strategies for winter wheat. Differences in NO₃‐N leaching largely reflected differences in SMN during autumn and winter. There was a tendency for lower yields in the NUE system, probably due to problems with couch grass. Overall, the measures for conserving N, when frequently used within a crop rotation, effectively reduced NO₃ concentrations in drainage water and NO₃‐N leaching losses, without severely affecting yield.     

Soil macropore dynamics affected by tillage and irrigation for a silty loam alluvial soil in southern Portugal

Soil tillage can have a significant effect on soil porosity and water infiltration. This study reports field measurements of near saturated hydraulic conductivity in an undisturbed soil under two tillage treatments, conventional tillage (CT) and minimum tillage (MT). The objective was to determine effective macro and mesoporosities, porosity dynamics during the irrigation season, and their contribution to water flow. Field observations were performed during the 1998 maize (Zea mays L.) cropping season in an Eutric Fluvisol with a silty loam texture, located in the Sorraia River Watershed in the south of Portugal. Infiltration measurements were done with a tension infiltrometer. At each location an infiltration sequence was performed corresponding to water tensions (φ) of 0, 3, 6 and 15 cm. Five sets of infiltration measurements were taken in both treatments in the top soil layer between May and September. One set of measurements was done at the depth of 30 cm at the bottom of the plowed layer in the CT plot. After 5 years of continuous tillage treatments the results show that regardless of the tillage treatment, saturated conductivity values K(φ₀) were several times larger than near saturation conductivity K(φ₃). This indicates that subsurface networks of water conducting soil pores can exist in both CT and MT maize production systems. In CT, the moldboard plow created macro and mesoporosity in the top soil layer while breaking pore continuity at 30 cm depth. This porosity was partially disrupted by the first irrigation, resulting in a significant decrease of 45% in the macropore contribution to flow. Later in the season, the irrigation effect was overlaid by the root development effect creating new channels or continuity between existing pores. In MT macroporosity contribution to flow did not show significant differences in time, representing 85% of the total flow. In both the treatments, macropores were the main contributing pores to the total flow, in spite of the very low macroporosity volumes.     

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.     

Assessment of tillage translocation and tillage erosion by hoeing on the steep land in hilly areas of Sichuan, China

Most of the tillage erosion studies have focused on the effect of tractor-plough tillage on soil translocation and soil loss. Only recently, have a few studies contributed to the understanding of tillage erosion by manual tillage. Furthermore, little is known about the impact of tillage erosion in hilly areas of the humid sub-tropics. This study on tillage erosion by hoeing was conducted on a purple soil (Regosols) of the steep land, in Jianyang County, Sichuan Province, southwestern China (30°24′N and 104°35′E) using the physical tracer method.

The effects of hoeing tillage on soil translocation on hillslopes are quite evident. The tillage transport coefficients were 26–38 kg m⁻¹ per tillage pass and 121–175 kg m⁻¹ per tillage pass respectively for k₃- and k₄-values. Given that there was a typical downslope parcel length of 15 m and two times of tillage per year in this area, the tillage erosion rates on the 4–43% hillslopes reached 48–151 Mg ha⁻¹ per year. The downslope soil translocation is closely related to slope gradient. Lateral soil translocation by such tillage is also obvious though it is lower than downslope soil translocation. Strong downslope translocation accounts for thin soil layers and the exposure of parent materials/rocks at the ridge tops and on convexities in the hilly areas. Deterioration in soil quality and therefore reduction in plant productivity due to tillage-induced erosion would be evident at the ridge tops and convex shoulders.     

Changes in total, mineralizable and light fraction soil organic matter with cropping and tillage intensities in semiarid southern Alberta, Canada

There has been a trend toward increased cropping intensity and decreased tillage intensity in the semiarid region of the Canadian prairies. The impact of these changes on sequestration of atmospheric CO₂ in soil organic carbon (C) is uncertain. Our objective was to quantify the changes in total, mineralizable and light fraction organic C and nitrogen (N) due to the adoption of continuous cropping and conservation tillage practices. We sampled three individual long-term experiments at Lethbridge, Alberta, in September 1992: a spring wheat (Triticum aestivum L.)-fallow tillage study, a continuous spring wheat tillage study and a winter wheat rotation-tillage study. Treatments had been in place for 3–16 years. In the spring wheat-fallow study, different intensities (one-way disc > heavy-duty cultivator > blade cultivator) of conventional tillage (CT) were compared with minimum tillage (MT) and zero tillage (ZT). After 16 years, total organic C was 2.2 Mg ha⁻¹ lower in more intensively worked CT treatments (one-way disc, heavy-duty cultivator) than in the least-intensive CT treatment (blade cultivator). The CT with the blade cultivator and ZT treatments had similar levels of organic C. The CT treatments with the one-way disc and heavy-duty cultivator had light fraction C and N and mineralizable N amounts that were about 13–18% lower than the CT with the blade cultivator, MT or ZT treatments. In the continuous spring wheat study, 8 years of ZT increased total organic C by 2 Mg ha⁻¹, and increased mineralizable and light fraction C and N by 15–27%, compared with CT with a heavy-duty cultivator prior to planting. In the winter wheat rotation-tillage study, total organic C was 2 Mg ha⁻¹ higher in a continuous winter wheat (WW) rotation compared with that in a winter wheat-fallow rotation. The lack of an organic C response to ZT on the WW rotation may have been due to moldboard plowing of the ZT treatment in 1989 (6 years after establishment and 3 years before soil sampling), in an effort to control a severe infestation of downy brome (Bromus tectorum L.). Our results suggest that although relative increases in soil organic matter were small, increases due to adoption of ZT were greater and occurred much faster in continuously cropped than in fallow-based rotations. Hence intensification of cropping practices, by elimination of fallow and moving toward continuous cropping, is the first step toward increased C sequestration. Reducing tillage intensity, by the adoption of ZT, enhances the cropping intensity effect.     

Interrill soil erosion as affected by tillage and residue cover

No-till cropping systems are effective in reducing soil erosion. The objective of this study was to determine whether high infiltration rates and low runoff and soil loss under long-term, no-till conditions in loessial regions of the Midwest US result from both the well-structured, porous condition of the soil and the protective cover of crop residue or primarily from residue cover. Soil loss, runoff, and infiltration were measured using a rainfall simulator on interrill erosion plots with and without residue cover on a conventional and two no-till systems in central Illinois. For both conventional till and no-till conditions, removing surface residue significantly decreased infiltration rates and increased soil loss. Tilling the no-till surface while maintaining an equal surface cover as with the no-till system slightly increased interrill erosion. Removing residue on a no-till system, however, increased soil loss significantly. A no-till soil condition without adequate residue cover will seal, crust, and erode with extremely high soil losses following surface drying.     

The structure of two alluvial soils in Italy after 10 years of conventional and minimum tillage

Micro and macroporosity, pore shape and size distribution, aggregate stability, saturated hydraulic conductivity and crop yield were analysed in alluvial silty loam (Fluventic Eutrochrept) and clay soils (Vertic Eutrochrept) following long-term minimum and conventional tillage. The soil structure attributes were evaluated by characterizing porosity by means of image analysis of soil thin sections prepared from undisturbed soil samples.

The interaggregate microporosity, measured by mercury intrusion porosimetry, increased in the minimally tilled soils, with a particular increase in the storage pores (0.5–50 μm). The amount of elongated transmission pores (50–500 μm) also increased in the minimally tilled soils. The resulting soil structure was more open and more homogeneous, thus allowing better water movement, as confirmed by the greater hydraulic conductivity of the minimally tilled soils. The aggregate stability was less in the conventionally tilled soils and this resulted in a greater tendency to form surface crusts and compacted structure, compared with the minimally tilled soils. The latter tillage practice seemed to maintain, in the long-term, better soil structure conditions and, therefore, maintain favourable conditions for plant growth. In the silt loam, the crop yield did not differ significantly between the two tillage systems, while in the clay soil it decreased in the minimum tilled soil because of problems of seed bed preparation at the higher surface layer water content.     

Nitrous oxide emissions and controls as influenced by tillage and crop residue management strategy

Mixed responses of soil nitrous oxide (N₂O) fluxes to reduced tillage/no-till are widely reported across soil types and regions. In a field experiment on a Danish sandy loam soil we compared N₂O emissions during winter barley growth following five years of direct drilling (DD), reduced tillage (RT) or conventional tillage (CT). Each of these tillage treatments further varied in respect to whether the resulting plot crop residues were retained (+Res) or removed (−Res). Sampling took place from autumn 2007 to the end of spring 2008. Overall N₂O emissions were 27 and 26% lower in DD and RT, respectively, relative to N₂O emissions from CT plots (P < 0.05). We observed that in residue removal scenarios N₂O emissions were similar for all tillage treatments, but in residue retention scenarios N₂O emissions were significantly higher in CT than in either DD or RT (P < 0.05). Irrespective of residue management, N₂O emissions from DD and RT plots never exceeded emissions from CT plots. Retention of residue was estimated to reduce emissions from DD plots by 39% and in RT plots by 9%, but to increase N₂O emissions from the CT plots by 35%. Relative soil gas diffusivity (Rdiff), soil NO₃-N, soil temperature, tillage and residue were important driving factors for N₂O emission (P < 0.05). A multiple linear regression model using Rdiff to represent the water factor explained N₂O emissions better than a water-filled pore space (WFPS) based model, suggesting a need for review of the current use of WFPS in N₂O prediction models. We conclude that on light textured soils, no-till has the potential for reducing N₂O emissions when crop residues are returned to the soil.     

The influence of organic matter in reducing the destabilization of soil by simulated tillage

Different agricultural practices can result in a decline in soil organic carbon (SOC) and a consequent reduction in soil structural stability. Experiments were conducted on soils with a range of SOC values, to quantify the destabilizing effects of increased tillage intensity. Different tillage intensity was simulated with the use of a falling weight, where specific energy levels, similar to those experienced during tillage, were reproduced. The level of destabilization was assessed by the quantity of mechanically dispersed clay (using a turbidimetric technique) and the quantity of water-stable aggregates (WSA) > 0.25 mm remaining after being shaken in water.

The quantity of clay dispersed increased with increasing water content, in the absence of any mechanical pretreatment, the rate of increase rising sharply with declining SOC. Following simulated tillage, and at water contents above the plastic limit, clay dispersion increased in proportion to the energy of disruption, and also increased with decreasing SOC levels. Below the plastic limit all the soils were relatively insensitive to mechanical disruption. A simple empirical model was derived to link clay dispersion to SOC, water content and energy of disruption.

The proportion of WSA declined sharply with decreasing SOC, and to a lesser extent following tillage. The quantity of WSA following simulated intensive tillage (300 J kg⁻¹) of grassland (SOC, 2.8–3.2 g (100 g)⁻¹) was greater than that present, prior to tillage from fallow, arable and arable/ley rotation treatments (SOC 1.1–2.5 g (100 g)⁻¹). Aggregate tensile strength was found to be relatively insensitive to differences in SOC. However, variations of strength within treatments, an indicator of soil friability, increased in proportion with SOC. A turbidity index was derived in which the turbidity of natural and remoulded aggregates was compared. Variation of this index with increasing mechanical energy is used as an indicator of the sensitivity of soils to damage during tillage. A visual representation is constructed to link the sensitivity of soils to damage during tillage with both SOC and water potential. These experiments illustrate that management practices, which lead to a long term reduction in SOC, are responsible for an increase in aggregate strength and reduction in stability plus an increase in sensitivity of soils to structural decline following subsequent tillage.     

Development and evaluation of a soil water evaporation model to assess the effects of soil texture, tillage and crop residue management under field conditions

Abstract. A number of mathematical models to predict soil water evaporation are available in the literature which generally require complex input data. In the present study, a simple parametric model has been developed by coupling existing and newly developed equations to assess soil water evaporation and drainage under field conditions in relation to potential evaporation rate, soil texture, time and depth of tillage and crop residue management. The model has moderate input data requirements and predicts well the effects of tillage and crop residue management practices on soil water loss (evaporation+drainage) with multi-drying and -wetting cycles prevailing under natural conditions. The root mean squares of deviations between observed and predicted cumulative water loss at different periods of study were 0.82, 2.04, 2.31 and 1.74  cm for untreated, residue-mulch, tillage and residue-incorporated treatments, respectively. Simulation analysis on cumulative evaporation and evaporation rate has shown that the evaporation reduction with different combinations of tillage and crop residue followed the order of residue-undercut>residue-mulch>residue-incorporated>tillage. Thus, the magnitude of beneficial effects of crop residues and tillage on soil water evaporation reduction are associated with amount of residues, mode of residue management (mulched or incorporated in the soil) and time and depth of tillage.