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

D'Annunzio sulla scena lirica: libretto o "Poema"?

Australia Direct Action climate change policy relies on purchasing greenhouse gas abatement from projects undertaking approved abatement activities. Management of soil organic carbon (SOC) in agricultural soils is an approved activity, based on the expectation that land use change can deliver significant changes in SOC. However, there are concerns that climate, topography and soil texture will limit changes in SOC stocks. This work analyses data from 1482 sites surveyed across the major agricultural regions of Eastern Australia to determine the relative importance of land use vs. other drivers of SOC. Variation in land use explained only 1.4% of the total variation in SOC, with aridity and soil texture the main regulators of SOC stock under different land uses. Results suggest the greatest potential for increasing SOC stocks in Eastern Australian agricultural regions lies in converting from cropping to pasture on heavy textured soils in the humid regions

The interaction of crop residue and fertiliser management and their effect on soil organic matter, soil physical properties and sustainability

The cultivation and cropping of soils across the Australian grain growing regions has resulted in substantial losses of soil organic matter (SOM). These losses have been accompanied by even greater losses in the active or labile components of SOM. Soil organic matter is an important indicator of sustainable farming systems as it has a central role in all aspects of soil fertility. The grain growing areas of northern New South Wales and southern Queensland in Australia are predominantly based on vertisol soils that have high water-holding capacities. This characteristic, along with initially high levels of fertility, has allowed reliable crop production on these soils in the past. Crop production systems in this area have increasingly used reduced tillage and the retention of crop stubble to increase soil water storage during the fallow period. Declining soil fertility has increasingly become evident but higher rates of N application have been successful in overcoming declines in grain yield and protein content. Studying changes in the concentration of soil organic matter due to different management practices requires methods that measure responsive and meaningful soil C fractions against large background concentrations. Changes in labile soil C fractions were measured using oxidation with 333 mM KMn0₄. The relative amounts of labile and nonlabile C (total C - labile C) were compared to a non-cropped reference soil and used to calculate a carbon management index (CMI). This study focused on increasing the understanding of crop residue breakdown and the influence of tillage and rotation practices on soil carbon fractions and the physical fertility of vertisol soils from the northern grains region. In the first study, two long-term trials established in 1981 were used to assess changes in soil fertility under different tillage and rotation management practices. The trials were located on a commercial property, "Gabo" near Croppa Creek, and at the Liverpool Plains Field Station, Breeza managed by NSW Agriculture. The study of changes in soil C fractions and soil physical fertility at the long-term trial at Breeza was complemented by a survey of commercial farming paddocks located on the Liverpool Plains in northern NSW. All the soils in the survey were black vertisol soils similar to the long-term trial site with an uncropped reference site located nearby. The final component of this study was a glasshouse-experiment using dual-isotope labelling with ¹³C and ¹⁴C to measure changes in soil carbon (C) due to residue decomposition and inputs from the growing crop. The influence of tillage and the type of crop residue were also investigated in this study

Understanding & managing N loss pathways : Minimising nitrogen losses to improve use efficiency in summer crops

• Over the past 3 years, we have had 6 experiments with isotope-labelled (15N) urea fertiliser in northern NSW and a further 11 in southern Qld, all focussed on measuring the fate of applied N fertilizer in summer sorghum. Normal fertiliser contains 14N so the use of 15N allows us to trace the fate of urea-N applied to the soil from sowing through to harvest. • Between 56 and 93% of the applied N was found in the soil and plant at harvest, with in-season rainfall (both timing and amount) and soil C and N status having a major impact on the seasonal loss potential. • Avoiding unnecessarily high N rates, delaying or splitting N fertiliser so that peak N availability coincides with peak crop N demand and relying on residual N from legume rotations all significantly reduced gaseous N losses from dryland sorghum, although the effectiveness of any management strategy varied with seasonal conditions. • Nitrification inhibitor-coated urea significantly reduced nitrous oxide emissions in all studies, but did not improve grain yields enough to justify the additional cost on an agronomic basis. • Depending on the season, delaying/splitting N applications gave either no yield benefit (dry season) or a significantly greater yield (good in-crop rainfall). Much of the unused N after a dry season remained in the soil and, provided loss events were not experienced during the fallow, significantly benefited the following crop. As reliance on N fertilizer increases, getting good crop recovery of applied N is essential Crop N recovery is most efficient when N is distributed through the root volume Gaseous losses of fertilizer N can be substantial, with denitrification of greatest concern for summer sorghum. Ensuring fertilizer N is in the crop or deeper in the soil profile is the best defence against loss Controlled release fertilizers can reduce denitrification but are rarely economic; legume N is effectiv

Legumes in Crop Rotations Reduce Soil Nitrous Oxide Emissions Compared with Fertilized Non-Legume Rotations

Soil nitrous oxide (N₂0) emissions were measured from a range of dryland crops and crop rotations in the northern grains region of Australia. The objective was to compare N₂0 emissions associated with the growth and post-harvest residue decomposition of a nitrogen (N₂)-fixing legume crop with that from N fertilized non-legume crops. From 2009 to 2012 a dryland crop rotation experiment was conducted on a black Vertosol (cracking clay soil) representative of the main soil type used for grain growing in the region. Crop rotation treatments were: canola + N_wheat + N_barley + N (CaWB), chickpea_wheat + N_barley (CpWB), chickpea_wheacchickpea (CpWCp), and chickpea_sorghum + N (CpS). Soil emissions of N₂0 were monitored in the field seven to eight times per day using an automated system of chambers connected to a gas chromatograph. Soil mineral N and plant N uptake were measured by regular field sampling. During the project, extremes of cold, hot, wet and dry weather were experienced that were often well below or above long-term averages for the site

Influence of source and quality of plant residues on emissions of N₂O and CO₂ from a fertile, acidic Black Vertisol

Few studies have compared emissions of nitrous oxide (N₂O), the potent greenhouse gas associated with decomposition of both below-ground (root) and above-ground (shoot) residues. We report a laboratory incubation experiment to evaluate effects of root and shoot residues from wheat, canola, soybean, and sorghum, incorporated into a naturally fertile acidic Black Vertisol, on N₂O and carbon dioxide (CO₂) emissions. The residue-amended Vertisol samples were incubated at 25 °C and 70 % water-filled pore space (WFPS) to facilitate denitrification activity for a total period of 56 days. The incubated soils were periodically sampled for N₂O, CO₂, mineral N, and dissolved organic carbon (DOC). In general, shoot residues emitted more CO₂ than roots, while N₂O emissions were 50-70 % higher in cereal root residues than those in shoots. Surprisingly, the highest N₂O emissions were associated with soils amended with the more inert high C/N ratio residues (wheat and sorghum roots), and to some extent, lowest emissions were associated with low C/N ratio (more labile) residues, particularly during the early stages of incubation (0-22 days). During this stage, there was a significant (p

Nitrous oxide emissions from acidic Black Vertosol: effects of residues, nitrogen additions and pH

Agricultural soils are a major source of atmospheric nitrous oxide (N₂O), a potent greenhouse gas contributing approximately 6% of the total radiative forcing from anthropogenic greenhouse gas emissions. Vertosols are the major soil type throughout much of the grain-growing areas of northern NSW and southern Queensland in Australia. In these areas, cultivation of grain legumes, retention of crop residues after grain harvest and increased use of fertilizer-nitrogen (N) are common practices, all of which are potentially important sources of N₂O emissions. Vertosols are fine-textured and have poor internal drainage, which can lead to greater periods of saturated, anaerobic conditions conducive to N₂O emissions through denitrification. This underlines the need to better understand the relative contribution of different N sources (i.e. fertilizer-N, crop residue-N, biologically-fixed N₂) to N₂O emissions from cropped Vertosols in order to define the least emitting system. The long-term aim is reduction of N₂O emissions from Australian agricultural systems. In the five experiments reported in this thesis, I examined the relative effects of fertilizer-N rates and biologically-fixed N₂ on N₂O emissions from an acidic Black Vertosol and further examined the effects of residue sources, particularly root versus shoot, and soil pH on N₂O emissions from the same soil