Ley Phase Research Articles

Effects of experimental drought and plant diversity on multifunctionality of a model system for crop rotation

In low-diversity productive grasslands, modest changes to plant diversity (richness, composition and relative abundance) may affect multiple ecosystem functions (multifunctionality), including yield. Despite the economic importance of productive grasslands, effects of plant diversity and environmental disturbance on multifunctionality are very rarely quantified. We systematically varied species richness, composition, and relative abundance of grassland ley communities and manipulated water supply (rainfed and drought) to quantify effects of diversity and environmental disturbance on multifunctionality. We then replaced the grassland leys with a monoculture crop to investigate ‘follow-on’ effects. We measured six agronomy-related ecosystem functions across one or both phases: yield, yield consistency, digestibility and weed suppression (grassland ley phase), legacy effect (effect on follow-on crop yield), and nitrogen fertiliser efficiency (full rotation). Drought reduced most ecosystem functions, although effects were species- and function-specific. Increased plant diversity affected mean performance, and reduced variation, across the six functions (contributing to multifunctional stability). Multifunctionality index values across a wide range of mixture diversity were higher than the best monoculture under both rainfed and drought conditions (transgressive over-performance). Higher-diversity, lower-nitrogen (150N) mixtures had higher multifunctionality than a low-diversity, higher-nitrogen (300N) grass monoculture. Plant diversity in productive grasslands is a practical farm-scale management action to mitigate drought impacts and enhance multifunctionality of grassland-crop rotation systems.

Increasing cattle slurry application to grass-clover leys of different ages did not affect nitrate leaching but increased legacy effect in mixed organic crop rotations

ContextOrganic dairy farms with grass-clover often have a large N surplus, due to biological N fixation and in addition, manure application, which challenges the efforts to reduce N losses. Potential loss pathways include leaching from grass-clover ley and subsequent crops, but if managed appropriately this N legacy effect may result in higher yields in the subsequent crops. ObjectiveTo investigate the fate of the ley phase N surplus including losses of nitrate in grass-clover leys, contribution to the N supply of the subsequent crop, and the contribution from the long-term slurry N application to grass-clover leys to nitrate leaching and yields in subsequent crops. MethodsWe quantified nitrate leaching across three years in two six-year crop rotations with two or four years of grass-clover ley and examined legacy effect of the grass-clover ley in relation to short- or long-term N fertilization levels. This was done by measuring water nitrate contents below the root zone combined with water balance modelling. ResultsNitrate leaching in 1- to 4-yr-old grass-clover leys were not influenced by cattle slurry application of up to 300 kg total-N ha-1 (equivalent to approximately 170 kg available N). Leaching losses were 2 - 19 kg N ha-1 yr-1 across grassland ages and application rates. Arable crops showed correspondingly low nitrate leaching (4–24 kg N ha-1 yr-1) except for barley/peas (74 kg N ha-1 yr-1), where a catch crop was established after autumn mechanical weed control. The legacy effect of fertilization on N yield was found in the first year following cultivation of 2-yr-old grass-clover swards and in both year one and two following cultivation of 4-yr-old grass-clover swards. The legacy effect was generally better predicted by the long-term cumulated fertilizer N application during the last rotation (six years) as compared to the most recent grass-clover N application rate. Nitrate leaching in the arable phase of the mixed crop rotations was not affected by fertilizer application in the ley phase. However, this might depend on catch crop strategy in the arable crops. ConclusionsNitrate leaching in dairy crop rotations was not influenced by cattle slurry application. It was found that both the short- and long-term slurry application history were able to explain the legacy effect and of those, the long-term was the best predictor. ImplicationsThe study shows that N leaching reduction targets can be met in an organic dairy crop rotation when attention is paid to the full crop rotation and utilization of short- and long-term legacy effects of slurry application.

Grassland legacy effects on yield of a follow-on crop in rotation strongly influenced by legume proportion and moderately by drought

We investigated the degree to which plant species diversity, drought and fertiliser level in a grassland ley can affect performance of a follow-on crop in a rotation. Grassland species and functional group diversity (grasses, legumes and herbs) were manipulated from monocultures to six-species mixtures in the grassland ley phase. A simulated two-month summer drought treatment was compared to a ‘rainfed’ control. Plots received 150 kg ha−1 yr−1 of nitrogen (N) fertiliser; additional replicates of L. perenne monoculture received 300 kg ha−1 yr−1 of N fertiliser. After two years, grassland communities were terminated, and each plot reseeded with an Italian ryegrass (Lolium multiflorum) model crop; its yield indicated the relative legacy effect of the preceding treatments (plant diversity, drought, N input). There was a modest but constant negative effect of drought on dry matter (−0.36 ± 0.091 t ha−1) and nitrogen yield (DMY and NY respectively) of the subsequent crop of L. multiflorum, across all plant communities. There were strong differences among the identity effects of the six former grassland species on DMY and NY of L. multiflorum. Legume species had the strongest effects on DMY of L. multiflorum (6.09 t ha−1 for the former T. pratense monoculture and 6.54 t ha−1 for T. repens). The lowest crop yield was from the former low-diversity high-input replicates (4.16 t ha−1 for former L. perenne monoculture with 300 kg ha−1 yr−1). There was no evidence that interspecific interactions in the grassland phase affected yield of the follow-on crop. Thus, the legacy effect of grassland mixtures was estimated by the identities and proportions of the species sown in the mixture. Similar patterns were obtained for NY. High-diversity, low-input grassland yielded more DMY and NY than low-diversity, high-input grassland (across both ley and follow-on crop phases). However, a legume proportion in the grassland ley of at least 33% is required to achieve high forage and crop performance in a grassland-crop rotation.

Yields and Nitrogen Dynamics in Ley-Arable Systems—Comparing Different Approaches in the APSIM Model

Nitrogen (N) dynamics in ley-arable cropping systems require better understanding in order to assess the potential of such systems to contribute to improved productivity and reduced nutrient losses in crop production. Large inputs of organic matter after termination of the ley phase result in increased mineralization and N availability to subsequent crops. The description and quantification of this residual N effect in ley-arable systems remains a major scientific challenge due to its variability and many influencing factors. Simulation modeling could contribute to improved understanding of N dynamics in ley-arable systems. The aim of this study was to evaluate the robustness of the Agricultural Production Systems Simulator (APSIM) to predict biomass yield, N yield, and N leaching of different forage maize systems in northwest Europe, while using two different approaches to predict the residual N effect. The evaluation was based on three field experiments covering plant phenology, biomass, N yield, and N leaching over several years. Model adjustments were necessary to describe mineralization of organic matter and release of N after ploughing of the grass leys. For this purpose, three scenarios were investigated by accounting for either (1) aboveground grass residues; (2) above- and belowground grass residues, both with the generic turnover approach in the model; or (3) N release depending on the carbon-to-N ratio of the residue compiled in a simple mineralization model (SMM). The results showed that APSIM-simulated biomass and N yield of maize were reasonable to poor across the different systems and sites, regardless of using the residue-related approach. The SMM performed more accurately compared to the generic turnover approach in predicting N leaching in a maize following a grass-clover ley. However, for all scenarios, APSIM had difficulties to predict a delay of N leaching observed in the experimental data after a pure ryegrass ley. In conclusion, the process description in APSIM related to organic matter mineralization in ley-arable systems under northwest European pedo-climatic conditions needs improved accounting of belowground grass residues, while the SMM is of added value to improve N mineralization patterns and leaching after a ley phase.

Can Regenerative Agriculture increase national soil carbon stocks? Simulated country-scale adoption of reduced tillage, cover cropping, and ley-arable integration using RothC

Adopting Regenerative Agriculture (RA) practices on temperate arable land can increase soil organic carbon (SOC) concentration without reducing crop yields. RA is therefore receiving much attention as a climate change mitigation strategy. However, estimating the potential change in national soil carbon stocks following adoption of RA practices is required to determine its suitability for this. Here, we use a well-validated model of soil carbon turnover (RothC) to simulate adoption of three regenerative practices (cover cropping, reduced tillage intensity and incorporation of a grass-based ley phase into arable rotations) across arable land in Great Britain (GB). We develop a modelling framework which calibrates RothC using studies of these measures from a recent systematic review, estimating the proportional increase in carbon inputs to the soil compared to conventional practice, before simulating adoption across GB. We find that cover cropping would on average increase SOC stocks by 10 t·ha−1 within 30 years of adoption across GB, potentially sequestering 6.5 megatonnes of carbon dioxide per year (MtCO2·y−1). Ley-arable systems could increase SOC stocks by 3 or 16 t·ha−1, potentially providing 2.2 or 10.6 MtCO2·y−1 of sequestration over 30 years, depending on the length of the ley-phase (one and four years, respectively, in these scenarios). In contrast, our modelling approach finds little change in soil carbon stocks when practising reduced tillage intensity. Our results indicate that adopting RA practices could make a meaningful contribution to GB agriculture reaching net zero greenhouse gas emissions despite practical constraints to their uptake.

Nitrous Oxide Emissions and Methane Uptake from Organic and Conventionally Managed Arable Crop Rotations on Farms in Northwest Germany

Land-use extensification by shifting from conventional to organic arable farming is often discussed as a measure for reducing greenhouse gas (GHG) emissions from agricultural land. Doubts about the benefits arise when emissions are calculated per product unit, particularly where high yields are possible under conventional management. Among the non-CO2 GHG emissions, nitrous oxide (N2O) is the main contributor from arable land and is controlled by soil type, environmental conditions and management. In order to investigate how land-use change from conventional to organic farming would perform under highly productive site conditions in northwest Germany, and how this would affect the important greenhouse gases N2O and methane (CH4), an on-farm field research was conducted over two experimental years. Two site-specific organic crop rotations, (i) with 25% legumes (grass + clover - winter wheat – winter rye – oats) and (ii) with 40% legumes (grass + clover – winter wheat – winter rye – spring field peas – winter rye), were compared with (iii) a conventional arable rotation (winter oilseed rape – winter wheat – winter wheat – sugar beet – winter wheat) and two reference systems, (iv) extensive grassland and (v) a beech forest), which were chosen as the baseline. The results showed that organic farming had lower N2O emissions of 0.7 N2O–N ha−1 year−1 than the conventional rotation, with 2.1 kg N2O–N ha−1 year−1 (p < 0.05), but higher emissions than the extensive grassland (0.3 kg N2O ha−1 year−1) and beech forest (0.4 kg N2O ha−1 year−1). CH4 emissions were a negligible part of total GHG emissions (as CO2 equivalents) in the two arable systems, and considerable uptake of CH4 from the forest soils showed this was a GHG sink in the first experimental year. Organic systems produced up to 40% lower crop yields, but the emissions per product unit in rotation (iii) was not superior to (ii) during the two experimental years. Thus, arable organic farming showed the ability to produce agricultural commodities with low N2O emissions per unit area, and no differences in product-related emissions compared with conventional farming. Conventional and organic systems both showed potential for further mitigation of N2O emissions by controlling the field level nitrogen surplus to a minimum, and by the optimized timing of the removal of the grass–clover ley phase.

Nitrate leaching in maize after cultivation of differently managed grass-clover leys on coarse sand in Denmark

When grass-clover leys have been ploughed nitrate leaching may increase. However, management of leys before or after ploughing may affect the leaching risk. We examined the effect of cultivating a six year ley, which the last two years had been treated differently (grazing only; spring cut followed by grazing, and spring and autumn cuts with grazing during the summer season only) on nitrate leaching in maize with/without a catch crop (per. ryegrass) and with/without slurry application (135kg total-Nha−1). An unfertilized barley harvested for silage with a catch crop of Italian ryegrass was used as reference. Shortening the grazing season in the grass-clover ley phase did not affect leaching after ploughing. In the following maize, the use of a perennial ryegrass catch crop in a high-yielding maize crop was not able to reduce nitrate leaching significantly, although leaching and maize yield tended to be lower with the catch crop. In unfertilized treatments both maize yields and nitrate leaching were significantly lower compared with treatments with slurry application. The unfertilized barley undersown with Italian ryegrass reduced leaching much more than unfertilized maize with perennial ryegrass as an undersown catch crop, despite yields of barley and ryegrass being less than half of the dry matter yields of unfertilized maize. The experiment illustrates that growing maize after ploughing of grass-clover leys without environmental consequences is difficult.

Influences of two-year red clover-grass ley management on nitrogen economy and following wheat performance

A two-year ley field experiment was established in May 2009 with six combinations of red clover, perennial ryegrass and cocksfoot, and two fallow control plots, to determine the impact of ‘cut and remove’ of the crops three times or ‘cut and mulch’ once annually on biomass yield, nitrogen (N) accumulation, soil mineralization and subsequent cereal performance. Farmyard manure was added to one of the fallow treatments at the beginning of the arable phase. The experiment was conducted on a clay loam soil at Moreton-in-Marsh, Gloucestershire, UK (NGR SP 217 323). During the ley fertility-building phase, there was no evidence that red clover (RC) had a synergistic effect on grass productivity when in mixtures, irrespective of cutting system. Accumulated above ground N over the 2 years was greater in cut/removed red clover-based leys (330–365 kg ha− 1) grass and fallow plots. In cut/mulched leys, RC was higher (113 kg ha− 1) than the rest. Soil potential mineralizable N (PMN) was not related to ley N yields but was consistently high in the red clover/ryegrass/cocksfoot (RCRGCF) treatments during winter and spring wheat. There was no indication that wheat yields and quality were improved following any red clover combinations or cutting regimes. These results suggest mixing RC with two grasses, RG and CF are likely to improve soil mineralization potential. Nevertheless, growing red clover leys over 2 years and mulching once annually under variable weather could limit soil N accumulation. In such conditions, growing red clover leys for a shorter period and removing herbage may be a better option.

Microbial biomass, microbial diversity, soil carbon storage, and stability after incubation of soil from grass–clover pastures of different age

A laboratory incubation study with clover grass pasture soils of seven different ages (0, 1, 2, 3, 4, 5, and 16 production years) was carried out to determine initial soil carbon (C) and nitrogen (N) stocks and potentials for greenhouse gas emissions (N2O and CO2). Compared with the soil from the recently established pasture, an increase of total soil C and N was observed along with pasture age. Greenhouse gas emissions were low and not significantly different among the soils from younger pastures (0–5 years), but especially N2O emissions increased markedly in the soil from 16-year-old grass–clover. Low emissions might mainly be due to an early C limitation occurring in the soils from younger pastures, which was also corroborated by decreasing levels of cold water-extractable C and early shifts within the microbial community. However, higher emissions from the old pasture soil were offset by its increase in total soil C. A longer ley phase without soil disturbance may therefore be beneficial in terms of overall C sequestration in systems with temporary grass–clover swards.

Integrating soil quality changes to arable agricultural systems following organic matter addition, or adoption of a ley-arable rotation

To study the sustainability of arable agricultural systems we examined a wide range of biological, physical and chemical properties associated with changes in soil quality. We integrated these using a qualitative multi-attribute model supported by the software tool DEXi to achieve a holistic estimation of soil quality. We tested the relative changes in soil quality attributes resulting from the incorporation of cattle slurry or green-waste compost, or from including a ley phase in the production of arable crops. We measured: abundances and biodiversity of the soil biota, physical properties and nutrient concentrations; twice in 2006 and thrice in 2007. These data were used to generate a model of soil quality, which showed that the addition of organic matter or a ley phase did increase soil quality. However, to fully understand the soil system results should be derived from a number of functionally related observations as there were opposing trends in individual observations. Increases in some beneficial attributes (such as decomposition, soil nutrient status and physical condition) were associated with an increased risk of nutrient losses from leaching and gaseous emissions. Assessing soil quality with only a few indicators may not identify these trade-offs. The multi-attribute modelling approach could identify the pathways responsible for changes in soil quality and identify possible environmentally detrimental effects.

Soil carbon storage and yields of spring barley following grass leys of different age

The inclusion of leys in arable cropping is generally found to improve soil fertility. The effect of leys depends on their botanical composition and management, but the significance of individual management factors remains confounded in most studies. We quantified the effects of one- to six-year-old grass-only leys on soil C (0–20 cm) and yields of three subsequent test crops of spring barley ( Hordeum vulgare) under-sown with Italian ryegrass ( Lolium perenne). Each ley was a mixture of four grass species ( Lolium perenne, Festuca pratensis, Phleum pratense, Poa pratensis), exposed to three to four cuts annually. Only mineral fertilizers were applied (225 kg N ha −1 yr −1). The yield of barley was tested at six rates of N fertilizer (0–150 kg N ha −1). The effect of leys on nitrate leaching losses was determined in a separate experiment. Grass yields were consistently high during the ley phase (11.2–12.5 t DM ha −1 yr −1), and the amount of N in grass cuts equalled that applied in fertilizers. The annual accumulation of soil C during the ley phase averaged 1.1 t C ha −1. Nitrate leaching losses were halved after ley establishment, remained low until the ley was ploughed, and returned then to pre-ley levels. In the first test crop, the grain yields of barley increased with ley age. However, addition of fertilizer N eliminated the benefits of older leys. In the second and third test crop, grain yields were unaffected by ley age. Although grain N contents in the first test crop were higher following older leys, fertilizer N rate was the dominant factor. More N was removed in barley grain plus straw than was added in N fertilizers (except at 150 kg N ha −1). The amount of soil C remained nearly constant during the test phase, probably due to the use of grass catch crops. We conclude that the main impact on soil fertility of non-leguminous leys, subject to cutting and well-balanced mineral N fertilizer management, is in the accumulation of soil C and reduction of leaching losses of soil nitrate, whereas effects on subsequent cereal crops are small and transient.

Assessment and maintenance of soil fertility in temperate organic agriculture.

Abstract The maintenance of soil fertility is a key tenet of organic farming and can be broadly defined as the ability of the soil to support the productivity of the system. The central concept of soil fertility in these systems is the use of legume-based multi-annual rotations together with the judicious use of on-farm manures. Rotations provide the opportunity for nutrient elements to be replenished, usually within a grass-clover ley phase with inputs of carbon and nitrogen (by the biological processes of photosynthesis and nitrogen fixation). We review evidence that shows that this 'building phase' of the rotations is also associated with increased biological activity and changes to the soil's physical characteristics. The sequence of crops within a rotation is designed to utilize changing levels of fertility and optimize the utilization of nutrient resources over the period of the rotation. Crops with high nutrient demand would therefore normally be placed at a point following the incorporation of a nutrient-rich ley phase. In some circumstances cover crops or undersown vegetation are appropriate to conserve nutrients and reduce losses at particular times within the cropping sequence. Where necessary, a small range of carefully controlled external inputs are allowed. The best methods of assessing soil fertility in organic farming depend upon longer-term and integrative assessments of the system such as crop yields or long-term changes in soil quality and organic matter rather than snapshot measurements of individual nutrient pools.

Nitrous oxide emissions, cereal growth, N recovery and soil nitrogen status after ploughing organically managed grass/clover swards

AbstractThe period after ploughing of grass–clover leys within a ley‐arable rotation is when nitrogen accumulated during the ley phase is most vulnerable to loss. We investigated how ploughing date and timing of cessation of grazing before ploughing affected nitrous oxide (N2O) losses of the first cereal crop. Ploughing dates were July and October for a winter wheat pilot study and January and March for spring barley in the main experiment. Timings of cessation of grazing (main experiment only) were October, January and March. Spring barley yield, nitrogen uptake and soil mineral nitrogen were also assessed. A separate large‐scale laboratory incubation was made to assess the effect of temperature and rainfall on nitrous oxide emissions and nitrate leaching under controlled conditions. Nitrous oxide emissions in the 1‐ to 2‐month period after autumn or spring ploughing, or sowing were typically between 20 and 150 g N ha−1 day−1 and increased with temperature and rainfall. Tillage for crop establishment stimulated N2O emissions with up to 2.1 kg N ha−1 released in the month after spring tillage. Cumulative nitrous oxide emissions were greatest (∼8 kg ha−1 over 17 months) after cessation of grazing in March before March ploughing, and lowest (∼5.5 kg ha−1) after cessation of grazing in January before January ploughing. These losses were 1.2–3.9% of the N inputs. In the laboratory study, winter ploughing stimulated nitrate leaching more than nitrous oxide emissions. The optimum time of ploughing appears to be early spring when the cold restricts nitrogen mineralization initially, but sufficient nitrogen becomes available for early crop growth and satisfactory N offtake as temperature increases. Early cessation of grazing is advantageous in leaving an adequate supply of residues of good quality (narrow C:N ratio) for ploughing‐in. Restricting tillage operations to cool, dry conditions, being aware of possible compaction and increasing the use of undersown grass–clover should improve the sustainability of organic farming.

Output and sustainability of organic ley/arable crop rotations at two sites in northern Scotland

Trials at Tulloch, Aberdeen (sandy loam soil, 820 mm rainfall) and Woodside, Elgin (light sandy loam, 730 mm) compared organically managed crop rotations containing different proportions of spring oats, swedes, potatoes and grass/clover leys (0·50 and 0·67 of the rotation at Tulloch; 0·38 and 0·50 at Woodside). The trials simulated farm conditions through the use of grazing animals and the recycling of farmyard manure. The rotations at each site gave similar financial outputs. Yields of oats were higher where these were grown after the main ley phase of the rotation than where they were grown later in the rotation (more ears/m2 and grains/ear), but were not significantly higher after a 4-year ley than after a 3-year ley at Tulloch. It was concluded that all of the rotations were agronomically and financially sustainable. Cereal yields showed large year-to-year variations but little indication of a progressive decline. There were only small changes in soil organic matter, soil P and soil K. Increased early summer weed cover in the arable crops was not matched by increases in weed invasion in the grass/clover leys and did not appear to be affecting yields.

Cultivation and Soil Organic Matter Management in Low Input Cereal Production following the Ploughing out of Grass Leys

Nitrogen fertility of low input cereal systems following ploughing out of grass leys is investigated using the soil nitrogen dynamics model SOILN with its linked cereal growth model, supported by a set of experimental data for spring and winter barley cropping. Soil organic matter (OM) plays an important part in transfer of fertility from the fertility-building ley phase to the fertility exploitation arable phase of ley-arable rotations. One aspect investigated is a possible role of ‘protected organic matter’, a component of soil OM which generally mineralises at a slow rate, but which becomes ‘unprotected’ so it mineralises at a somewhat faster rate for a limited period following disturbance of the soil by ploughing. Measurements of CO2 emissions in the laboratory and field support the concept of protected OM. In simulations with the SOILN model, this is represented by a temporary increase in the value of the humus decomposition rate constant for a few weeks following ploughing. The assumption of raised humus decomposition rates after ploughing makes some improvements to fits of simulations with the linked models to measured grain and straw yields and N offtakes, as well as giving a more realistic decline in soil OM over successive years of cereal cropping. Predictive simulations demonstrate how, in the absence of mineral N fertiliser, cereal crop yields decline over the years following ploughing out of leys, but yields can be maintained by making applications of organic manure or slurry.

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.

Is the productivity of organic farms restricted by the supply of available nitrogen?

Abstract. This paper reviews information from the literature and case studies to investigate whether productivity in organic systems is restricted by the supply of available N during the major phases of crop growth. Organic systems have the potential to supply adequate amounts of available N to meet crop demand through the incorporation of leys, N rich cash crop residues and uncomposted manures. However, this is seldom achieved because leys are only incorporated once every few years and organically produced crop residues and manures tend to have low N contents and slow mineralization rates. N availability could be improved by delaying ley incorporation until spring, applying uncomposted manures at the start of spring growth, transferring some manure applications from the ley phase to arable crops, preventing cover crops from reaching a wide C:N ratio and better matching crop type with the dynamics of N availability.

A comparison of triple superphosphate and Gafsa ground rock phosphate fertilisers as P-sources for grass-clover swards on a poorly-drained acid clay soil

Organic farming practice prohibits the use of triple superphosphate (TSP) as a source of phosphorus. As basic slag is not now generally available, interest is focused on the relative value of ground rock phosphate (GRP). A comparison of TSP and Gafsa GRP was made during 1988–92 as to their ability to increase DM production under cutting from newly sown grass/white clover swards established in 1987 on an acid clay soil in SW England. Averaged over the different P fertiliser inputs and years, the DM yield was 8.0 t ha-1 y-1 (range 6.93–9.81) compared to 6.3t ha-1y-1 (range 6.00–7.71) without added P. Lime was added at either 3 or 6t ha-1 in 1987, and at half these rates in 1990. Whereas the yield improved by 45% with P at the lower rate of lime, it improved only by 12% at the higher rate. When P fertiliser was applied annually at 30 kg ha-1, TSP was superior to GRP, but when applied in one initial dose of 120 kg ha-1, GRP was superior over the subsequent 4 year period. There was no consistent effect of the addition of either P or lime on the clover content of the sward. The alkaline bicarbonate soil test (Olsen P) was a good predictor of available P within a given year; there was a general reduction of P availability over the course of the experiment. Mechanisms to explain the longer term effectiveness of GRP are postulated and discussed. It is concluded that farmers who are limited to using GRP rather than TSP would suffer a yield penalty over the longer term of 11.5%, and that P fertilizer for the ley phase in a rotation should be incorporated in one dose at the outset.

Physical rehabilitation of degraded krasnozems using ley pastures

The physical fertility of krasnozems and euchrozems (Red Ferrosols) in Australia has declined substantially as a result of continuous cropping. Much of this decline is associated with reduced levels of soil organic carbon and soil compaction due to vehicle trac when soils are too wet. We examined the impact of kikuyu (Pennisetum clandestinum) and Rhodes grass (Chloris gayana) pasture leys with various management inputs on the regeneration of physical fertility of continuously cropped krasnozems from 2 locations in the South Burnett region of southern Queensland. Pasture leys significantly improved the physical fertility of continuously cropped soils within 2–4 years. The most significant effects were on the creation of improved surface and subsurface macroporosity, and in a reduction in surface crust formation under high energy rain due to improved aggregate stability. Final steady state infiltration rates under well-managed leys increased 4-fold compared with those in continuously cropped soil. Pastures were unable to ameliorate compacted layers below approx. 15 cm, although significant improvements in hydraulic conductivity through these layers (and to depths of at least 70 cm) were made, presumably by creating of continuous biopores. Introduced earthworms improved pasture effectiveness in ameliorating this layer, but only to depths of 20 cm, while deep ripping during the ley phase was the most effective treatment. Kikuyu was the more effective pasture species in overcoming soil physical infertility, particularly in terms of improving aggregate stability under rain. In addition, the ability of kikuyu to resist the compacting influence of cattle trampling during wet weather meant that rainfall infiltration eciency was maintained during the ley phase and management options on returning to cropping were more flexible (e.g. direct drill strategies can be used). However, if pastures were ungrazed, the advantages of kikuyu in soil physical restoration were evident in only 2 years.

Nitrogen supply to no-tillage crops, as influenced by mulch type, soil type and season, following pasture leys in the semi-arid tropics

Past cropping research in the semi-arid tropics of northern Australia has shown that in this climate and on the predominantly sesquioxidic soils, recovery of fertiliser nitrogen (N) by crops is often low. Conceptually, no-tillage, legume ley farming offers features for coping better with the constraints of climate, soil and high fertiliser transport costs to this remote region. This paper summarises the N cycle in a system in which pastures provide N for successive crops, and mulch at the time of crop establishment is provided by the killing of new pasture growth. The aim was further to provide a sound foundation for managing N supply in relation to demand in a climate that causes high variation and uncertainty for pasture N2 fixation and sequestering, the amount of early season re-growth (mulch), rate of mulch decomposition, nitrate leaching losses, and crop growth and N demand. The research approach combined field studies with simulation modelling. A series of field studies that included bare fallow and grass and legume pasture leys on clay loam and sandy loam soils, were conducted at Katherine over 4 wet seasons to study subsequent mineralisation of N. Experimental results were used to test the performance of a simulation model for predicting the observed variations consequent upon the various management options. Experimental results showed that the carbon (C) : N ratio of the residue and soil texture were important factors in determining N mineralisation, immobifisation, and nitrate leaching following chemical kill of pasture leys. However, the greatest variation was between seasons. A modified version of the CERES-Maize N model was able to simulate the accumulation of nitrate following a bare fallow and following pasture leys with high levels (above and below ground) of freshly killed residues with widely differing C:N ratio, the downward movement of nitrate-N in the soil and the interaction of these processes with seasonal rainfall. Despite a capability for simulation of the soil N dynamics in a cropping phase following pasture leys, ex~erimental results indicated how nitrate distribution following leys is influenced by pasture growth during the ley, and how this varied greatly with season and soil texture. The simulation capability reported here has been incorporated elsewhere into the development of a full system model, embracing both the ley phase and the crop phase.