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To comprehensively evaluate the impact of agricultural management practices on soil productivity, it is imperative to conduct a thorough analysis of soil bacterial ecology. Deep‐banding nutrient‐rich amendments is a soil management practice that aims to improve plant growth and soil structure by addressing the plant‐growth constraints posed by dense‐clay subsoils. However, the response of bacterial communities to deep‐banded amendments has not been thoroughly studied. To address this knowledge gap, we conducted a controlled‐environment column experiment to examine the effects of different types of soil amendments (poultry litter, wheat straw + chemical fertiliser and chemical fertiliser alone) on bacterial taxonomic composition in simulated dense‐clay subsoils. We evaluated the bacterial taxonomic and ecological group composition in soils beside and below the amendment using 16S rRNA amplicon sequencing and robust statistical methods. Our results indicate that deep‐banded amendments alter bacterial communities through direct and indirect mechanisms. All amendments directly facilitated a shift in bacterial communities in the absence of growing wheat. However, a combination of amendments with growing wheat led to a more pronounced bacterial community shift which was distinct from and eclipsed the direct impact of the amendments and plants alone. This indirect mechanism was evidenced to be mediated primarily by plant growth and hypothesised to result from an enhancement in wheat root distribution, density and rhizodeposition changes. Therefore, we propose that subsoil amendments regardless of type facilitated an expansion in the rhizosphere which engineered a substantial plant‐mediated bacterial community response within the simulated dense‐clay subsoils. Overall, our findings highlight the importance of considering the complex and synergistic interactions between soil physicochemical properties, plant growth and bacterial communities when assessing agricultural management strategies for improving soil and plant productivity. [ABSTRACT FROM AUTHOR]

Deep placement of organic amendments such as poultry litter and legume residues has been developed as a technique to ameliorate sodic clay subsoils in the south‐east Australian cropping region. It has been suggested that the soil microbial community plays a key role in this process of subsoil amelioration. A controlled environment experiment using repacked soil units was conducted to investigate changes in the microbial communities of subsoil treated with organic and inorganic amendments. Poultry litter, inorganic nutrients and wheat straw plus inorganic nutrients with equivalent total nutrient content (460 kg N ha−1, 210 kg P ha−1 and 330 kg K ha−1) were mixed into a central band and incubated for 21 days, followed by 126 days with wheat plants. Changes to bacterial and fungal communities in the bulk subsoil, 2–7 cm from the amended band, were assessed using next‐generation amplicon sequencing of the 16S and ITS rRNA genes. There were small but significant (p < 0.05) changes in bacterial and fungal community structure of the amended treatments, relative to the unamended control, which were linked to the movement of solutes away from the amended band. The three amendments did not affect microbial community composition differently in the bulk soil, although there were changes in the relative abundance of selected taxa. Our results suggest that changes in soil microbial communities in the bulk subsoil in this experimental system largely depended on movement of the soil solution through the profile. Highlights: We characterized effect of amendments on microbial communities in the soil beyond the detritusphere.Microbial community of bulk soil was different in amended treatments from the unamended control.Amendments did not affect community composition differently but did change relative abundances of certain taxa.Changes in microbial community structure were due to movement of soil solution away from the amendment. [ABSTRACT FROM AUTHOR]

Osmotic adjustment (OA) and increased cell-wall extensibility required for expansive leaf growth are well defined components of adaptation to water stress in dry soil, which might interact with soil phosphorus (P) concentration and defoliation frequency for intensively grazed white clover in legume-based pasture. Experiments were conducted with frequently and infrequently defoliated mini-swards of white clover growing in dry soil with low and high P concentrations. The higher yielding high-P plants were able to dry the soil to greater soil water suctions; their leaves had lower water potential values, yet they showed fewer water stress symptoms and underwent a more complete recovery from the water stress-symptoms on rewatering, than the low-P plants. High-P plants had greater OA, proline concentration and leaf expansion rate. On the other hand, low-P plants showed an increased osmotic concentration when there was no change in the total solute content per unit of leaf d. wt. indicating more loss of water from the leaf tissue. The key measures that appeared to be directly associated with plant recovery over a short period following water stress were increased proline concentration and leaf expansion rate, probably resulting from increased cell-wall extensibility rather than increased production of cells for the high-P plants. [ABSTRACT FROM AUTHOR]

Increased leaf phosphorus (P) concentration improved the water-use efficiency (WUE) and draught tolerance of regularly defoliated white clover plants by decreasing the rate of daily transpiration per unit leaf area in dry soil. Night transpiration was around 17% of the total daily transpiration. The improved control of transpiration in the high-P plants was associated with an increased individual leaf area and WUE that apparently resulted from net photosynthetic assimilation rate being reduced less than the reductions in the transpiration (27% vas 58%). On the other hand, greater, transpiration from low-P plants was associated with poor stomatal control of transpirational loss of water, less ABA in the leaves when exposed to dry soil, and thicker and smaller leaf size compared with high-P leaves. The leaf P concentration was positively related with leaf ABA, and negatively with transpiration rates, under dry conditions (P <0.001). However, leaf ABA was not closely related to the transpiration rate, suggesting that leaf P concentration has a greater influence than ABA on the transpiration rates. [ABSTRACT FROM AUTHOR]