A cheaper and faster method is needed to determine soil mineralogy. The traditional methods include X-ray diffraction, and a laboratory determined ratio of negative charge per unit weight of clay. In this paper, mid-infrared spectroscopy was used to predict this ratio, providing a cheaper and faster alternative to traditional methods.

The plastic limits of soil can yield information on soil mechanical behaviour, which is important in relation to soil compaction and soil tillage. We found that the plastic limits of arable soils are strongly dependent on soil organic matter content. We present equations for estimation of the plastic limits from soil texture and organic matter content, which could be valuable in the development of models of agricultural systems that include tillage as affected by climate and soil type.

Conventional methods of assessing soil carbon by sampling representative soil profiles fail to account for the full range of soils that occur in a landscape. Our study randomly selected soil samples and showed that associated method error was largely related to soil spatial variability. We conclude that a stratified sampling approach, which proportionally samples the full range of soils that exist in a landscape, is preferable to random or representative sampling strategies.

The role of soil organic matter in boron turnover and bioavailability is often underestimated. The sources and mechanisms of boron supply to plants are still poorly understood. The results of the present investigation indicated that the fate of soil boron is determined primarily by processes in the system ‘plants–soil humus compounds’.

Surface conductivity of clay is an important contributor to soil salinity. The dependency of surface conductivity of bentonite clay on temperature and water content was quantified in terms of its rate of change with temperature over the range of water contents. This information is useful for designing underground barrier with bentonite and for managing salinity of clay soil where temperature and water content of the soil vary over time.

Previous research has measured losses of soil C some of New Zealand’s pasture soils. We found, in a laboratory experiment, that cow urine causes soil C to move into solution in both pine and pasture soils. Therefore, cow urine deposition may lead to a loss of soil carbon, but field testing is required.

Controlling nitrogen loss from agricultural soils is essential to prevent surface water contamination. We evaluated surface runoff and the losses of nitrogen in various forms from different cropping systems and found that the losses in peak events accounted for the most of nitrogen losses. Our research results have implications for the choice of cropping systems and best management practice for agricultural farms to reduce nitrogen loads to water bodies.

Dicyandiamide (DCD) can be applied to soil to protect the essential plant nutrient nitrogen (N) from loss from the soil.  We measured the loss of DCD itself from soil and showed it is highly mobile in water and losses can be large under high rainfall.  It is important to understand this so that individual sites/soil types can be managed appropriately to make effective use of the DCD and contribute to a sustainable agriculture.

Soil fertility management practices can influence the activities of beneficial soil microbes such as arbuscular mycorrhizal fungi (AMF). The effects of fertilizer application on AMF occurrence and colonisation were studied in maize/Centrosema pascuorum and sole maize systems. The study showed that a maize/Centrosema system can maximise AMF benefits to increase yield and also reduce fertiliser input into agricultural soils and thereby minimise cost input for farmers.