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Context: The grain-growing areas of north-eastern Australia are a major producer of grain for human and livestock consumption, but declining soil nitrogen (N) and phosphorus (P) fertility is increasing fertiliser requirements to sustain productivity. Adding a concentrated zone of fertiliser P to the subsoil (i.e. a 'deep P' band) is an effective strategy to increase plant P uptake in farming systems reliant on stored soil water. However, crop responses to deep P with contrasting soil N status remain unclear. Aim: This study aimed to assess responses of sorghum (Sorghum bicolor) to fertiliser P with contrasting distributions of soil N. Method: A lysimeter experiment was conducted in semi-controlled environment, where sorghum was grown to physiological maturity in P depleted Vertosol with contrasting fertiliser N and P additions. Key findings: Responses of sorghum to deep P were optimised when bands were placed in N enriched soil in the 0–20 cm layer, producing comparable biomass to when P was dispersed throughout the soil volume. Localised root proliferation around the deep P band was maximised when bands were placed into N-enriched soil, however plant P uptake was only 77% of that with dispersed P. Conclusions: Sorghum responses to deep P were affected by the distribution of soil N within the top 60 cm of the soil profile, with maximum dry matter production, N and P uptake occurring when high concentrations of N and P were co-located in the 0–20 cm layer. Implications: Adequate N status of the upper soil profile is required to optimise sorghum responses to deep P. Applying concentrated bands of P to the subsoil ('deep P') increases plant P uptake in cropping systems reliant on stored soil water. However, we determined that sorghum (Sorghum bicolor) deep P responses can be limited by delayed N access, with biomass accumulation, productive tillering and P uptake maximised when N was concentrated in the 0–20 cm soil layer compared to at depth. Growers should ensure adequate N status of the upper soil profile to optimise sorghum deep P responses. [ABSTRACT FROM AUTHOR]

It is unequivocal that human activities have increased emissions of greenhouse gases, that this is causing warming, and that these changes will be irreversible for centuries to millennia. Whilst previous studies have broadly examined the contribution of agriculture or land use change to anthropogenic greenhouse gas emissions, the contribution of soil itself remains unclear, with quantifying the contribution of soil in this regard being critical for developing and implementing appropriate management practices. In the present study, we used previously published datasets for carbon dioxide, nitrous oxide, and methane to determine soil-based emissions of greenhouse gases and their contribution to anthropogenic greenhouse gas emissions. We show that our near-complete reliance on soil to produce the rapidly increasing quantities of food being demanded by humans has caused soil to release profound amounts of greenhouse gases that are threatening the future climate. Indeed, net anthropogenic emissions from soil alone account for 15 % of the entire global increase in climate warming (radiative forcing) caused by well-mixed greenhouse gases, with carbon dioxide being the most important gas emitted from soil (74 % of total soil-derived warming), followed by nitrous oxide (17 %) and methane (9 %). There is an urgent need to prevent further land use change (including for biofuel production) to limit the release of carbon dioxide that results from the loss of soil organic carbon, to develop strategies to increase nitrogen fertilizer efficiency in order to reduce nitrous oxide emissions, to decrease methane from rice paddies, and to ensure that the widespread thawing of permafrost is avoided. Innovative approaches are urgently required for reducing greenhouse gas emissions from soil if we are to limit global warming to 1.5 or 2.0 °C. [ABSTRACT FROM AUTHOR]

Phosphate-solubilising microorganisms (PSM) are often reported to have positive effects on crop productivity through enhanced phosphorus (P) nutrition. Our aim was to evaluate the validity of this concept. Most studies that report 'positive effects' of PSM on plant growth have been conducted under controlled conditions, whereas field experiments more frequently fail to demonstrate a positive response. Many studies have indicated that the mechanisms seen in vitro do not translate into improved crop P nutrition in complex soil-plant systems. Furthermore, associated mechanisms are often not rigorously assessed. We suggest that PSM do not mobilise sufficient P to change the crops' nutritional environment under field conditions. The current concept, in which PSM solubilise P 'for the plant' should thus be revised. Although PSM have the capacity to solubilise P to meet their own needs, it is the turnover of the microbial biomass that subsequently provides P to plants over a longer time. Therefore, the existing concept of PSM function is unlikely to deliver a reliable strategy for increasing crop P nutrition. A further mechanistic understanding is needed to determine how P mobilisation by PSM as a component of the whole soil community can be manipulated to become more effective for plant P nutrition., (© 2020 The Authors New Phytologist © 2020 New Phytologist Trust.)