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The incorporation of cover crops in orchards and vineyards can increase soil organic carbon (OC) and improve nitrogen (N) availability. This study compared how three herbaceous under-vine cover crop assemblages affected OC and N pools in four edaphically distinct vineyard agroecosystems. Using physical fractionation and soil spectral analysis we: 1) compared effects of grass and legume mono- and poly-cultures on total, coarse (≥50 µm) and fine (

With diminishing world reserves of phosphorus (P) deposits and rising fertilizer prices, it is important to find alternate sources of P for crops. The aim of this research was to evaluate the effect of four different composts C1 (animal manure and straw), C2 (garden waste), C3 (wood chips and bark), and C4 (kitchen waste) on soil P pools and P uptake by wheat on 14, 28, and 72 days after compost application. The composts were applied as a 2.5 cm thick layer on the soil surface. During sampling, only the soil underlying compost was sampled. Soil pH and total organic carbon were not affected by the amendments. Soil respiration was significantly higher in compost-amended soils compared with the unamended soil except with C4 on day 72. Addition of composts increased plant growth, and P uptake being highest on day 72 with C1 and C4. With little effect on available P concentration on day 14, there was a conversion of organic P into inorganic P in the compost treatments suggesting net mineralization of o...

Improved understanding of the effect of compost application on soil properties is critical for optimizing the desired effects of compost application. However there are no studies on the effect of composts on soil properties within the first centimetres of the compost layer. In this microcosm study three composts from different feedstocks, namely C1 (from animal manures) and C2 and C3 (from the organic fraction and municipal solid waste) were applied as a layer which was separated from the soil by a mesh. Microcosms without compost served as controls. Microbial and chemical properties of the soil were determined at 0–5 and 5–10 mm distance from the mesh after 30 and 63 days. During the 63 day incubation, the total C, N and P and available N concentrations in the composts decreased whereas the available P concentration increased. The composts induced higher microbial biomass and activity, total organic C and available N and P concentrations up to 10 mm into the surrounding soil with greater effects after 30 than after 63 days. The increase in nutrient concentrations was generally greater in soil adjacent to the two finer-textured composts with the higher nutrient concentration (C1 and C3) than in the coarser-textured compost (C2) which had lower nutrient concentrations, however the differences in nutrient concentrations in the soil were small compared to those among the composts. The 0–5 and 5–10 mm layers did not differ in most of the measured properties except for greater soil respiration and N and P availability in the 0–5 mm layer. It is concluded that composts release nutrients into the surrounding soil over a period of 2 months which increase nutrient availability and microbial activity, with the zone of influence extending at least 10 mm from the compost-soil interface.

Little is known about the decomposition rates of shoot and root residues of perennial grasses. This knowledge is important to estimate the carbon sequestration potential of the grasses. An incubation experiment was carried out in a sandy clay loam with shoot and root residues of three native perennial grasses (Wallaby grass, Stipa sp. and Kangaroo grass) and the annual grass barley either separately or in mixtures of two residues. Respiration rate was measured over 18 days, and microbial C and available N were measured on days 0 and 18. Decomposition was lower for roots than for shoots and lower for residues of perennial grasses than for barley. Cumulative respiration was positively correlated with water-soluble C in the residues but not with residue C/N. In the mixtures, the measured cumulative respiration was higher than the expected value in five of the nine mixes usually where the differences in cumulative respiration between the individual residues were relatively small. Lower than expected cumulative respiration were found in two of the mixtures in which barley shoots (high cumulative respiration) were mixed with residues with low cumulative respiration. There was a negative correlation between the change in microbial biomass C concentration from day 0 to day 18 and cumulative respiration on day 18. In the amended soils, the available N concentration decreased from day 0 to day 18. It is concluded that the low decomposition rate of perennial grasses residues should favour C sequestration, but that mixing residues of similar decomposition rate may accelerate their decomposition.

The poor solubility of rock phosphate limits its usefulness for crop production, but it has been shown that combined application of rock phosphate with plant residues can increase its P availability compared to rock phosphate alone. To investigate if compost mulch has a similar effect as residues, the effect of two rock phosphates [Nutriphos Guano Powder (RPA) and Indian Potash Limited (RPB)] with or without two different composts C1 (from garden waste) and C2 (from wood chips and bark), on soil P pools and P uptake by wheat was evaluated in a 75-day glasshouse experiment in a loamy sand soil. The composts were applied as a 2.5-cm-thick layer on the soil surface and rock P was mixed in the soil at a rate of 0.250 g kg−1 soil (equivalent to 35 mg P kg−1 of RPA and 26 mg P kg−1 soil as RPB). Further treatments included an unamended soil and a soil amended with soluble P (KH2PO4) at a rate of 50 mg P kg−1 soil. Wheat was sown and harvested after 42 and 75 days. At sampling, the compost layer was removed and the underlying soil was sampled. Soil pH and total organic C concentration were not affected by the amendments. Soil respiration was significantly higher in soil amended with composts with or without rock P compared to unamended and inorganic fertiliser treatments. On day 75, addition of composts alone or with rock P increased plant growth and P uptake by 30–50 % compared to the unamended soil, which was greater increase than with soluble P. Compared with either rock P or compost applied alone, the combination of rock P with compost increased the concentration of NaHCO3-Pi and microbial P by about 30 %, suggesting that compost increased the mobilisation of rock P. The combination of compost and rock P also changed the concentrations of non-labile P pools compared to rock P alone indicating effects on P flux between the pools. This study showed that surface compost application can increase P mobilisation from rock P, but plant growth and P uptake were not increased compared to compost alone indicating that the composts supplied sufficient P to the plants.

Although the beneficial effects of compost on soil properties are well known, there are few systematic studies comparing the effects of composts on soils of different textures. The aim of this pot study was to assess the effects of a single application as mulch of two types of composts derived from different feedstocks, namely C1 (from garden waste) and C2 (from agricultural residues and manures) on three soils with different clay contents (46%, 22% and 13%, hereafter referred to as S46, S22 and S13) in terms of their physical, chemical and biological properties as well as on plant growth and nutrient uptake. The composts were placed as 2.5-cm-thick mulch layer on the soil surface, and wheat plants were grown for 35 days and to grain filling (70 days). The composts reduced the soil pH by 0.3–0.7 units, slightly increased total organic C, but increased soil electrical conductivity compared to unamended soil. Soil respiration was significantly higher in S13 than S46 in all treatments after 5 weeks. At grain filling, soil respiration was higher in S13 than in the other two soils and higher with C2 than with C1 and in the non-amended soil. The addition of compost significantly increased soil cation exchange capacity (CEC) in S22 and S46, but not in S13 which also had the lowest CEC among the soils. C2 increased the available P concentration and macro-aggregate stability in all soils compared to C1 and the unamended soil. Compost addition increased available N in S46 and S22 compared to the unamended soil with a stronger effect by C1. Both composts increased wheat growth and shoot P concentrations with the effect of C2 being greater than that of C1. It is concluded that the effect of composts varies with soil type as well as compost type and that this interaction needs to be taken into account when composts are applied to improve specific soil properties.

Composts with different feedstocks may have differential effects on soil properties and plant growth which, may be further modulated by soil texture. In a 77-day pot experiment in the glasshouse, we investigated the effect of a single application as mulch of six types of composts derived from different starting feedstocks in two soils (13% and 46% clay, referred to as S13 and S46) on soil physical, chemical and biological properties, plant growth and nutrient uptake. Composts were placed as 2.5 cm thick mulch layer on the soil surface and wheat plants were grown and harvested at 42 days and at 77 days (grain filling). Composts differed in total and available N and P and particle size with C1, C3, C4 and C5 being fine-textured, whereas C2 and C6 were coarse-textured. Compost addition as mulch increased soil total organic C and EC, but had no effect on pH. In all treatments, cumulative soil respiration was higher in S13 than in S46 and was increased by compost addition with the greatest increase with C2 and C6. Compared to the unamended soil, most compost mulches (except C2) increased macroaggregate stability. Compost mulches significantly increased available P and N in both soils, except for C2. Compost mulches increased available N up to 6-fold in both soils with the strongest increase by C5. Most composts also increased wheat growth and shoot P and N concentrations with the greatest effect on plant N concentration by C5 and on plant P concentration by C4. However, C2 decreased shoot N and P concentrations compared to the unamended soil. Most compost mulches (except C2) increased mycorrhizal colonization by up to 50% compared to the unamended soil. Fine-textured compost mulches generally had a greater effect on soil properties and plant growth than coarse-textured composts. Despite distinct differences between the soils with respect to clay content, TOC and available P, the effect of the compost mulches on soil and plant properties was quite similar.

Indigenous cover crops have the potential to promote an increase in natural enemies providing fortuitous control of pest species and other ecosystem services. We test this idea in a vineyard in south eastern Australia, where reduced water availability because of drought coupled with increased temperatures has generated interest in sustainable alternatives to the exotic perennial cover crops commonly planted. Three endemic perennial cover crops, comprising the grasses Austrodanthonia richardsonii and Chloris truncata and a mix of two saltbushes (Atriplex semibaccata and Atriplex suberecta) were established as cover crops and compared with introduced oats (Avena sativa). Abundance of a range of predators and parasitoids was higher in vines with native cover crops compared with the oat control. In addition, predation levels of sentinel eggs of a common vineyard pest, light brown apple moth (Epiphyas postvittana), were increased in the native cover crops. However, the native cover crops also increased the abundance of some potential pest species. Native plants therefore have potential to increase abundance of beneficial invertebrates that assist in pest control, but need to be used carefully to ensure that they do not increase local pest problems.

Maintenance of available phosphorus (P) is a problem faced by both conventional and organic systems but it is exacerbated in the latter given that manufactured inorganic sources of P fertiliser are not permitted under the International Federation of Organic Agriculture Movements certification guidelines. The focus of this paper is a discussion of potential agronomic strategies to assist in sustainable management of the soil P resource in organic and low-input broadacre farming systems within the Australian rain-fed cereal–livestock belt. The paper considers three broad strategies for agronomic management of P in this context and draws on reported research from overseas and within Australia. An analysis of the current knowledge suggests that the option most likely to ensure that soluble P is not a limitation in the system is the importation of allowable inputs that contain P from off-farm, although for much of the Australian cereal–livestock belt the immediate issue may be access to economically viable sources. Research targeted at quantifying the economic and biological benefits to the whole-farm system associated with the adoption of these practices is required. Improving the P-use efficiency of the system by incorporating species into rotation or intercropping systems that are able to use P from less soluble sources has been a successful strategy in parts of the world with climate similar to much of the Australian cereal–sheep belt, and deserves further research effort in Australia. Agronomic management to maximise quantity and quality of pasture and crop plant residues undoubtedly builds labile soil organic matter and facilitates P cycling, but the strategy may be of limited benefit in low-rainfall areas that do not have the capacity to produce large biomass inputs. Evidence that organic or low-input systems naturally increase the numbers and diversity of soil organisms is sparse and published studies from Australian systems suggest that P nutrition is not enhanced. However, seed and soil microbial inoculants to facilitate improved P uptake have been developed and are currently being field tested in Australia. Progress in selection and breeding for cereal genotypes that are more P efficient and other plant genotypes that can use less labile P sources, is gaining momentum but still remains a long-term prospect, and may involve genetic modification which will not be acceptable for organic systems.