Soil phosphorus status in organic and conventional vegetable farms in Southeast Queensland, Australia

The soil phosphorus (P) status (0-10 cm) of two farming systems (organic (OF) and conventional (CF) vegetable farms) at two locations (Gatton and Stanthorpe) was examined amongst a suite of soil fertility indicators. The P status was similar between farming systems, in contrast to some broad-acre organic systems. Examination of farm management records revealed substantial overlap between P inputs at both localities with CF systems also receiving organic inputs, e.g. green manure and composts. A statistical analysis of the effects of different inputs also indicated that P fertility did not vary significantly between farms. Soil P levels were medium to high across farm types indicating a potential environmental risk for vegetable producers particularly in sandy well drained soils. The three methods of extraction Colwell, Olsen and Resin were well correlated with each other and produced similar results indicating the similar nutrient pools exist between farming system

Paddock Scale Water Quality Monitoring of Vegetable-Sugarcane and Legume-Sugarcane Farming Systems - Summary report 2010-2013 Burnett Mary Region

The project has delivered a number of key findings from what were years in which summer rainfall was 50‐100% greater than the long term average. These were as follows – - Sediment and nutrient losses during grain legume or vegetable rotations with sugarcane were dominated by losses occurring during the sugarcane crop. - The most sensitive period for soil and nutrient loss occurred during the transition period between crops in the rotation, and during the early stages of crop establishment. - Soil disturbance, the presence of groundcover (crop residues/trash/living mulch) and soil compaction were the major factors affecting runoff volumes and loads of sediment and total nitrogen (N) and phosphorus (P). The most effective management systems that ameliorated soil compaction, minimised soil disturbance and maintained ground cover reduced sediment and nutrient loads by 50‐60%. - Legume residues or legume companion crops were effective at providing groundcover and at reducing soil loss, but also tended to increase losses of the biologically active fractions of N (Dissolved Inorganic N) and P (Filterable Reactive P). - Runoff losses of DIN were relatively small in all systems tested (0.7‐ 2.7 kg DIN/ha), but leaching losses of nitrate‐N were estimated in excess of 140 kg N/ha from the current commercial practice intensive vegetable systems. This leached N was lost before being able to be recovered by the subsequent sugarcane crop and represents a risk to groundwater quality. - The risk of offsite losses from herbicides with long half‐lives in the field was illustrated by high concentrations of Diuron recorded in runoff that occurred more than 2.5 months after herbicide application. There was also concern about increased losses of Metribuzin when applied in systems with reduced tillage and surface residues/trash. - Similarly effective weed control during the plant cane crop could be achieved by reduced application rates of residual herbicides and/or the replacement of residual herbicides with less persistent knockdown products. However, excluding Diuron in the ratoon crop resulted in poor weed control and the need for additional herbicide applications. - The most substantial improvements in runoff (if not drainage) water quality were achieved at the expense of cropping system productivity – especially in the systems with intensive vegetables. The management strategies showing most promise involve strategic/zonal tillage, reduced nutrient inputs and reduced rates of residual herbicide use. These promising systems will need research attention to fine tune management so as to limit constraints to productivity and profitability

Carbon losses in terrestrial hydrological pathways in sugarcane cropping systems of Australia

Climate change and carbon (C) sequestration are a major focus of research in the twenty-first century. Globally, soils store about 300 times the amount of C that is released per annum through the burning of fossil fuels (Schulze and Freibauer 2005). Land clearing and introduction of agricultural systems have led to rapid declines in soil C reserves. The recent introduction of conservation agricultural practices has not led to a reversing of the decline in soil C content, although it has minimized the rate of decline (Baker et al. 2007; Hulugalle and Scott 2008). Lal (2003) estimated the quantum of C pools in the atmosphere, terrestrial ecosystems, and oceans and reported a “missing C” component in the world C budget. Though not proven yet, this could be linked to C losses through runoff and soil erosion (Lal 2005) and a lack of C accounting in inland water bodies (Cole et al. 2007). Land management practices to minimize the microbial respiration and soil organic C (SOC) decline such as minimum tillage or no tillage were extensively studied in the past, and the soil erosion and runoff studies monitoring those management systems focused on other nutrients such as nitrogen (N) and phosphorus (P)

Ανάλυση και βελτιστοποίηση της επίδοσης cloud εφαρμογών σε διαμοιραζόμενα περιβάλλοντα με προσαρμοστική ανάθεση πόρων

Intensive tillage, high fertiliser inputs, and plastic mulch on the soil surface are widely used by vegetable growers. A field investigation was carried out to quantify the impact of alternate land management and fertiliser practices designed to improve offsite water quality on the productivity of vegetable rotations within a sugarcane farming system in a coastal region of subtropical northeast Australia. Successive crops of capsicum and zucchini were grown in summer 2010–2011 and winter 2011, respectively, using four different management practices. These were ‘Conventional’—the current conventional practice using plastic mulch, bare inter-rows, conventional tillage, and commercial fertiliser inputs; ‘Improved’—a modified conventional system using plastic mulch in the cropped area, an inter-row vegetative mulch, zonal tillage, and reduced fertiliser rates; ‘Trash mulch’—using cane trash or forage sorghum residues instead of plastic mulch, with reduced fertiliser rates and minimum or zero tillage; and ‘Vegetative mulch’—using Rhodes grass or forage sorghum residues instead of plastic mulch, with minimum or zero tillage and reduced fertiliser rates. During the second vegetable crop (zucchini), each management practice was split to receive either soil test-based nutrient inputs or a common, luxury rate of nutrient addition. The ’Trash mulch’ and ‘Vegetative mulch’ systems produced up to 43% lower capsicum and zucchini yields than either of the plastic mulch systems. The relative yield difference between trash systems and plastic mulch management systems remained the same for both the soil test-based and high nutrient application strategies, suggesting that factors other than nutrition (e.g., soil temperature) were driving these differences

Soil property differences and irrigated-cotton lint yield— Cause and effect? An on-farm case study across three cotton-growing regions in Australia

The average lint yield of irrigated cotton in Australia ranges from 2270 to 3700kg/ ha, but yields vary substantially between farms and also between fields on the same farm. Differences in soil properties may cause these yield variations. Identifying which factors are causal and what management can be implemented to mitigate the impacts should help optimize inputs and improve profits. During the 2018–2019 summer cotton-growing season, a paired-field comparison approach was used to investigate and improve the understanding of soil property induced irrigated cotton yield differences within five farms across three regions of NSW, Australia. The paired fields at each farm recorded an average lint yield difference of >284kg/ha (measured in 2018–2019 or 5-year average lint yield). Several soil properties differed between the paired fields at each farm comparison. The soil organic carbon stocks were higher in the higher-yielding fields at all the farm comparisons and the normalized lint yield percentage was positively correlated with soil organic carbon stocks. Soil sodicity was higher in the lower yielding fields at 3 of the 5 comparisons. Results for most soil nutrient tests were above the recommended critical concentrations for Australian cotton production. A stepwise linear regression excluding soil nutrients that were above soil test critical values for crop response and below crop toxicity levels indicated the lint yield was positively correlated with SOC stocks and negatively correlated with sodicity and bulk density. No earthworms were detected during visual soil assessment or soil sampling across all the sites. Visual soil assessment was not a sensitive predictor of cotton crop performance. Comparing soil properties using a paired field approach may assist cotton growers in understanding the factors behind yield differences. A similar strip comparison approach could be adopted for within-field variability by dividing the fields into discrete performance zones and assessing the soil properties of each zone separately.284kg/ha (measured in 2018–2019 or 5-year average lint yield). Several soil properties differed between the paired fields at each farm comparison. The soil organic carbon stocks were higher in the higher-yielding fields at all the farm comparisons and the normalized lint yield percentage was positively correlated with soil organic carbon stocks. Soil sodicity was higher in the lower yielding fields at 3 of the 5 comparisons. Results for most soil nutrient tests were above the recommended critical concentrations for Australian cotton production. A stepwise linear regression excluding soil nutrients that were above soil test critical values for crop response and below crop toxicity levels indicated the lint yield was positively correlated with SOC stocks and negatively correlated with sodicity and bulk density. No earthworms were detected during visual soil assessment or soil sampling across all the sites. Visual soil assessment was not a sensitive predictor of cotton crop performance. Comparing soil properties using a paired field approach may assist cotton growers in understanding the factors behind yield differences. A similar strip comparison approach could be adopted for within-field variability by dividing the fields into discrete performance zones and assessing the soil properties of each zone separately

Contrasting agricultural management effects on soil organic carbon dynamics between topsoil and subsoil

Agricultural practices (e.g. tillage, crop rotation and fertiliser application) have a strong influence on the balance between carbon (C) input and output by altering physicochemical and microbial properties that control decomposition processes in the soil. Recent studies suggest that the mechanisms by which agricultural practice impacts soil organic carbon (SOC) dynamics in the topsoil may not be the same as those in the subsoil. Here, we assessed SOC stock, soil organic fractions and nitrogen availability to 1.0 m in soils under a cotton (Gossypium hirsutum L.)-based cropping system, and assessed the impact of agricultural management (three historical cropping systems with or without maize (Zea mays L.) rotation) on SOC storage. We found that the maize rotation and changes in the particulate organic fraction influenced SOC stock in the topsoil, although the overall change in SOC stock was small. The large increase in subsoil SOC stock (by 31%) was dominated by changes in the mineral-associated organic fraction, which were influenced by historical cropping systems and recent maize rotation directly and indirectly via changes in soil nitrogen availability. The strong direct effect of maize rotation on SOC stock, particularly in the subsoil, suggests that the direct transfer of C into the subsoil SOC pool may dominate C dynamics in this cropping system. Therefore, agricultural management that affects the movement of C within the soil profile (e.g. changes in soil physical properties) could have a significant consequence for subsoil C storage

Phosphorus uptake in faba bean, field pea, and corn cultivars from different sources: preliminary studies of two options for organic farmers

Low soil phosphorus (P) availability commonly limits yield in Australian broadacre organic production systems where superphosphate fertiliser is not permitted, and alternative P nutrition strategies are sought. Glasshouse experiments were conducted to investigate the potential of faba beans (Vicia faba L.) (FB), or field peas (Pisum sativum L.) (FP), grown in acidic sandy loam or alkaline clay, to accumulate P, which could then be supplied to a subsequent crop as part of a green manure rotation or after harvest. Another experiment investigated differences in growth and P acquisition between corn (Zea mays L.) cultivars: Hycorn 424 (a modern hybrid), and four traditional cultivars used in organic production. The experiments were carried out under conditions of P stress and had rock phosphate (RP), poultry manure (PM), or single superphosphate (SP) applied at 50 kg P/ha. For FP, maximum P input to the soil from incorporation would occur at or after pod initiation. However, P uptake by both legumes in both soils from sparingly soluble RP was low, with fertiliser P-use efficiencies of 0–1.3% compared with 1.8–12.7% for PM and 6.1–9.9% for SP. In the corn experiment, P fertiliser source had much larger effects than cultivar on plant biomass and P uptake, with responses generally ranked SP >PM>> RP > Control. Hycorn 424 generally produced higher dry matter and P uptake than the traditional cultivars under all P treatments. The implications of these preliminary investigations for Australian broadacre organic agriculture are discussed

Nitrogen losses in terrestrial hydrological pathways in sugarcane cropping systems of Australia

The Australian Great Barrier Reef (GBR) is one of the world's best known natural ecosystems (Devlin and Schaffelke 2012). The catchments that drain into the GBR are best known for productive agricultural land that supports extensive grazing enterprises as well as croplands supporting sugarcane (Saccharum spp.), banana (Musa spp.), vegetables, cotton (Gossypium hirsutum L.), and grain industries. The sugar industry is based in closest proximity to the GBR lagoon, with sugarcane farms predominantly located in the coastal areas of these catchments. Sugarcane fields therefore have the potential to impact the quality of water entering the GBR lagoon through off farm movement of nutrients and pesticides, so careful management is warranted to limit any offsite impacts. Recent management practice changes in these coastal cropping systems have led to small but significant reductions in nutrient and sediment loads (Fabricius et al. 2014). Lower nitrogen (N) fertilizer rates have resulted in some reduction in offsite N movement (Webster et al. 2012), but the extent to which further N rate reductions are possible without having an impact on sugarcane productivity has yet to be explored. In this article, we discuss the impact of contrasting management systems on N losses in runoff from sugarcane farmin

Isotopic tracing of phosphorus uptake in corn from ³³P labelled legume residues and ³²P labelled fertilisers applied to a sandy loam soil

In low input (e.g. organic) farming systems where soil phosphorus (P) fertilisers such as superphosphate are not used, maintaining sufficient available soil P for plant growth can be a major challenge. The use of P accumulating cover crops may increase P availability for subsequent crops. We hypothesised that P release from organic residues of legumes (faba bean ('Vicia faba') and field peas ('Pisum sativum')) could supply adequate P to meet the needs of a subsequent crop in a low P soil. A pot experiment was conducted to determine the contribution of P by legume green manure to subsequent corn using ³³P labelled legume residues and ³²P labelled inorganic fertiliser (KH₂PO₄). The treatments included two rates of P application, (a) 10 kg P ha⁻¹ as legume root and shoot residues or as inorganic fertiliser with and without a C source, and (b) 38 kg P ha⁻¹as a combination of legume shoot and root residues or a combination of root and inorganic fertiliser and inorganic fertiliser alone. An absolute control (zero P) was also used. Shoot dry matter, P uptake and P source (residues or fertilisers) of total P in corn were measured at harvest. Faba bean and field pea residues alone or in combination with fertilisers contributed up to 10% and 5% of the total P uptake by corn respectively, compared with up to 54% by inorganic fertilisers. Incorporation of field pea and faba bean residues with P concentrations higher than those observed under field conditions, may not always lead to adequate net P release to supply the early growth phase of subsequent crops

Increasing soil organic carbon with maize in cotton-based cropping systems: Mechanisms and potential

In a rotation, the use of crop species with large root biomass is thought to increase soil organic carbon (SOC) storage deeper in the soil profile, yet the processes and mechanisms that control SOC dynamics at depth are poorly understood. Using a cotton-based field trial, we examined how maize may impact SOC dynamics up to 1 m depth in three systems that differed in tillage and wheat rotation by examining the changes in δ13C signature of SOC and soil C fractions associated with maize during a two-year period. The inclusion of maize increased the whole-profile SOC stock, particularly in the subsoil under minimum tillage and wheat rotation. The increase was associated with the stable C fraction, and could not be attributed solely to the C contribution from maize root biomass alone. We propose that C movement in the form of dissolved organic C (DOC) may have contributed to the observed increase in SOC stock. The strong temporal changes and the possible mechanisms behind the increase suggest that the introduction of maize into cotton-based cropping systems may not yield a consistent benefit. This study highlights the role of DOC in subsoil C stock and the importance of understanding whole-profile SOC dynamics in evaluating the potential of management practice in increasing SOC stock