Conservation Agriculture Practices Increase Potentially Mineralizable Nitrogen: A Meta-Analysis

Potentially mineralizable nitrogen (PMN) is considered an important indicator of soil health. Cropping systems management can affect PMN. However, the effect size and relationship with crop yield across specific management practices remain uncertain. We conducted a quantitative review to understand how conservation agriculture management practices affect PMN including N fertilizer application, cropping system diversity, and tillage system as well as the relationship of crop yield with PMN. Data were extracted from 43 studies published in peer-reviewed journals, providing 494 paired comparisons of PMN and 26 paired comparisons of PMN and yield across selected crop management practices. In our meta-analysis, the effect size for each management practice was expressed as a response ratio, calculated as PMN or yield for the fertilizer application, high crop diversity, and no-till system to the no-fertilizer, less diverse crop system, and tillage system. On average, N-fertilized cropping systems had greater PMN: compared to no N fertilizer, inorganic N fertilizer had 22%, and manure had 34% higher PMN. Diverse cropping systems also had greater PMN: three or more different crops in rotation had 44% greater PMN than continuous cropping systems; cropping systems with a leguminous cover crop had 211% greater PMN than systems without cover crops. Compared to till systems, no-till systems had 13% higher PMN. Overall, conservation practices consistently increased both PMN and yield; however, the increase in PMN and yield were not correlated. Consistent with the use of PMN as a soil health indicator, this synthesis demonstrates that practices benefiting PMN also benefit yield

Quantifying the impact of microbes on soil structural development and behaviour in wet soils

There is evidence that microbial populations play an important role in altering soil pore geometry, but a full understanding of how this affects subsequent soil behaviour and function is still unclear. In particular the role of microorganisms in soil structural evolution and its consequence for pore morphological development is lacking. Using a combination of bio-chemical measurements and X-ray Computed Tomography (CT) imaging, a temporal comparison of microscale soil structural development in contrasting soil environments was made. The aim was to quantify the effect of microbial activity in the absence of other features likely to cause soil deformation (e.g. earthworms, roots etc.) on soil structural development in wet soils, defined by changes in the soil porous architecture i.e. pore connectivity, pore shape and pore volume during a 24 week period. Three contrasting soil textures were examined and changes compared between field soil, sterilised soil and a glucose enhanced soil treatment. Our results indicate that soil biota can significantly alter their microhabitat by changing soil pore geometry and connectivity, primarily through localised gaseous release. This demonstrates the ability of microorganisms to modify soil structure, and may help reveal the scope by which the microbial-rich rhizosphere can locally influence water and nutrient delivery to plant roots