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The sustainability of using irrigation to produce food depends not only on the availability of sufficient water, but also on the soil's 'response' to irrigation. Stocks of carbon (C) and nitrogen (N) are key components of soil organic matter (SOM), which is important for sustainable agricultural production. While there is some information about the effects of irrigation on soil C stocks in cropping systems, there is a paucity of such studies in pastoral food production systems. For this study, we sampled soils from 34 paired, irrigated and unirrigated pasture sites across New Zealand (NZ) and analysed these for total C and N. On average, irrigated pastures had significantly (P < 0.05) less soil carbon (C) and nitrogen (N) than adjacent unirrigated pastures, with differences of 6.99 t C ha and 0.58 t N ha in the uppermost 0.3 m. Differences in C and N tended to occur throughout the soil profile, so the cumulative differences increased with depth, and the proportion of the soil C lost from deeper horizons was large. There were no relationships between differences in soil C and N stocks and the length of time under irrigation. This study suggests SOM will decrease when pastures under a temperate climate are irrigated. On this basis, increasing the area of temperate pasture land under irrigation would result in more CO in the atmosphere and may directly and indirectly increase N leaching to groundwater. Given the large and increasing area of land being irrigated both in NZ and on a global scale, there is an urgent need to determine whether the results found in this study are also applicable in other regions and under different land management systems (e.g. arable).

There is a significant relationship between the tree communities and the soils in the Mooiplaas- Mahlangeni region of the central Kruger National Park. Shrub savanna dominated by Colophospermum mopane (mopane) as a multiplestemmed shrub occurs on all the fine-textured soils derived from basic rocks i.e. basalts, diabase and olivine gabbro. Mixed savanna woodlands dominated by either mopane or Combretum apiculatum (red bushwillow) occur on the coarse-textured soils derived from granitic gneiss. The red bushwillow is dominant on the more shallow soils. Mopane occurs in very dense stands as either stunted trees or as single-stemmed shrubs on most duplex soils. Relatively low-lying areas with saline soils are treeless. Terminalia sericea (silver cluster- leaf) is characteristic of deeper coarse-textured and somewhat poorly drained soils

Soil carbon stock change between two major land uses in New Zealand was measured by sampling paired plots across the boundaries of low productivity grassland and forest planted pre‐1990. The national soil carbon monitoring system uses low productivity grassland as a benchmark to evaluate soil carbon stock change for other land uses. The goal was to validate earlier estimates of the effect of pre‐1990 afforestation and to reduce their level of uncertainty. We selected a set of sites to represent the national stocks of forests planted pre‐1990. Previous studies derived estimates of the land‐use effect on soil carbon for afforestation ranging from +1.6 to −8.5 t/ha to 30 cm depth. For all estimates, the 95% confidence interval spanned zero. Our study used nine of the previous paired‐plot sites and sampled and analysed 21 new sites. The land‐use effect of change from grassland to forest planted pre‐1990 was estimated at −17.4 t/ha. The 95% confidence interval ranged from −10.1 to −24.6 t/ha and did not include zero change. The result supported the soil carbon monitoring system assumption that forests planted pre‐1990 have significantly lower soil carbon stocks than the low‐productivity‐grassland standard. Evidence of stock change occurred in depth increments to 0.2 m but with no significant change for the 0.2–0.3 m increment. This suggests that the sampling depth of 0.3 m was adequate for the estimation of soil carbon stock change.