Volume One 15. Resource Quality (Water, Air, Soil) Though it is easy to take for granted, we depend on our soil resource, particularly its quality. Soil quality refers to the biological, chemical and physical state of the soil and the maintenance of soil ecosystems. A range of factors contribute to soil quality, including soil structure, water holding capacity, soil fertility and organic matter content. Deteriorating soil quality will adversely affect the productive capacity of the soil and all of the other important functions currently performed by soil resources. Maintaining and enhancing soil quality is therefore a significant issue. Issue 15F – Some land use activities or practices have the potential to adversely affect soil quality. Soil quality is fundamental to the environmental and economic wellbeing of Marlborough. It is therefore important that land use activities are undertaken in a manner that does not degrade soil quality. Land use activities, or land management practices associated with particular activities, can change the biological, chemical and physical state of the soil and in doing so may adversely affect soil quality and productivity. Degradation of the soil resource is not always obvious and can occur progressively over a long period of time. It is difficult to establish the extent and severity of soil degradation in Marlborough as limited soil quality monitoring has been carried out. There are considered to be some major problems relating to soil quality and what monitoring that has been done indicates that in some cases primary production has resulted in soil compaction and elevated levels of nutrients/trace elements. Soil compaction and changes to the nutrient status of soils are of particular concern. Heavier clay-based soils are more vulnerable to soil compaction than alluvial soils, particularly when they are heavily stocked or worked under wet conditions. Frequent use of heavy vehicles/machinery in the same location is also likely to cause soil compaction. Soil compaction increases soil bulk density, reduces aeration and decreases infiltration. In turn, these changes adversely affect pasture and crop growth and lead to increased water and nutrient runoff. Increased water runoff can have significant drainage implications, especially if existing drainage infrastructure is unable to manage the increased volume and rate of runoff. Soil organic matter is central to many functions in soils. It is an important source of nutrients, contributes to a stable soil structure, helps retain and store water and nutrients added to soil, and provides a source of energy for soil microbes. The maintenance of organic matter in soils therefore makes a significant contribution to soil quality. Activities such as frequent cultivation of soils and the removal of vegetation can result in low organic matter status in soils. A low organic matter status puts soils at risk of poor aeration, poor drainage and soil structure degradation, all of which can potentially negatively affect crop productivity and predispose soil to a range of environmental issues (such as erosion loss). Soil contains essential mineral elements required by plants and animals. An inevitable consequence of the productive use of soil is that, at some time in the future, soils will become unable to sustain high levels of production unless those nutrients are replaced. Soil depletion refers to the reduction of soil nutrients to a level where their potential to sustain primary production is adversely affected. Although fertiliser use has decreased over time in Marlborough, many primary producers still apply it to maintain the nutrient status of the soil and therefore soil productivity. Excessive fertiliser application creates the potential for nutrients such as nitrogen and phosphate to runoff into adjoining rivers and wetlands or leach into underlying groundwater. Other elements may also be added to the soil, especially through the application of liquid wastes and in some cases the irrigation of water. For example, sodium can be a significant component of wastewater. Soils with elevated sodium concentrations have the potential to cause a range of adverse effects, including soil structural deterioration (which can reduce water infiltration and hydraulic conductivity) and reduction in plant growth. As land use change occurs and our understanding of the soil resource improves, there is the potential for other soil quality issues to emerge. For example, a trend toward re-contouring of 15 – 37