Iron oxides are the most abundant metallic oxides in soils, and are an important source and sink of trace elements. However, the nature of the association between trace elements and the iron oxides has not been established. The results of this study showed that iron oxides contained various trace elements, and the dissolution rates of iron oxides were very low, therefore, iron oxides is an important role for predicting the availability of trace elements in soils.

Protecting shallow groundwater from pollutants originating at the soil surface requires management strategies that build on accurate models to predict pollutant transport to the groundwater. This study demonstrated that stochastic transport models that account for heterogeneity in small-scale transport parameters obtained from laboratory tests provide a practical and computationally efficient tool to describe heterogeneous solute transport at large spatial scales. Based on such simple predictive models, the fate of surface-applied chemicals under different land-management scenarios can be tested.

Conversion of forests to pastoral agriculture generally results in increased losses of nitrogen via undesirable pathways such as nitrate leaching and nitrous oxide. In this study total nitrogen and the natural abundance of nitrogen isotopes in soils increased along three forest-to-pasture chronosequences, while the carbon to nitrogen ratio declined. Simple measurements of total nitrogen, total carbon, and the natural abundance of nitrogen isotopes in soils could be a useful indicator of past land management and nitrogen losses.

Soils store huge amounts of carbon (C) and nitrogen (N) as organic matter which affects the global C and N balance. Land management can alter the organic matter content of soils. Some areas of New Zealand are converting plantation pine forest to pastures for dairy farming. We found the soils under long-term pasture had more C and N than under pines, and accumulation was more rapid in the early years after conversion. Establishment of dairy pastures on previously forested soil has increased their capacity to store C and N as organic matter.

Biochar applications potentially can improve soil quality and sequestrate carbon in soils. The effects change with biochars produced with different feedstock materials and under different temperatures. The information from this study should be useful to design soil carbon sequestration strategies with different biochars.

The influence of soil organic carbon accumulation on soil phosphorus availability along with forest ecosystem development is a controversial issue. Here, we explored the relationships among organic carbon, sequentially extracted phosphorus fractions and phosphorus sorption index in surface soils of eight mature subtropical forests in China, and found generally positive relationships among them. This finding suggests that accumulation of organic carbon may increase the availability of phosphorus in surface soil in mature subtropical forests.

Biological soil quality of minimum-till pasture was compared to undisturbed, virgin soil. Conversion of virgin soil to cultivated pasture soil under irrigation enhanced soil organic matter levels, microbial activity and ecosystem functionality. Therefore, soil biological health was improved.

New Caledonian Ferralsols are very poor in nutrients, leading to slow plant growth. In parallel, disposal of sewage sludge is a significant problem. Thus, applying the sludge to improve soil fertility seems an economically and environmentally viable solution. Amendment of bare soil with sewage sludge enhanced plant growth while the dosage applied affected plant diversity.

Woody perennials that can penetrate hard soils may establish themselves during the first season and are more likely to survive. We found that some tree species thicken their roots more and maintain higher growth rates than other species. We also observed a modest relationship between the relative root elongation rate in very hard soils and the maximum root growth pressure that four different tree species can exert. Variations in root growth relate to intrinsic characteristics and natural abundance of species in different environments.

Carbon utilisation efficiency represents the assimilated fraction allocated to microbial growth. Nitrogen addition can significantly affect soil microbial biomass and carbon utilisation efficiency. The information from this study may be useful in better understanding of the carbon and nitrogen cycling in the soil.