Sustainability of New Zealand high‐country pastures under contrasting development inputs. 4. Organic matter components

Abstract

Biomass, N, S, P, C, and Ca composition of shoots, litter, roots and coarse organic matter > 1.3 mm diam., and <2 mm soil fraction are given for two trials under 61 different fertiliser and grazing treatments on a Pukaki/Tekapo high-country soil after 10-15 years. Effects were primarily related to fertiliser, secondarily to stocking rate, and rarely to the grazing method. While there was an increase in soil C and N and a decrease in C/N ratio of the <2 mm soil fraction with increasing fertiliser rate, the relationships were weak. Spring shoot biomass increased with S and P fertiliser rate and decreased with stocking rate. Surface litter (5-33 t ha -1 ) was slightly greater under lax grazing, but total soil root and coarse organic matter (6-57 t ha -1 ) increased with stocking rate, with an exponential decrease with soil depth. There were only small treatment effects on %N in organic components, %S in organic matter components increased with S fertiliser rates, and %P increased with P fertiliser rates, especially in the litter layer. There were active roots to 40 cm soil depth. The half-life of leaf litter decomposition of 10 species from April to September ranged from 0.2 to 38 years. The decomposition rate of litter was positively correlated with C/N and Ca litter concentration over the first fortnight after deposition and with %S in litter over the next 150 days. Microbial biomass decreased with fertiliser level. An incubation experiment indicated that nitrification was occurring. Grazing management treatments had greater effects on soil organic components than on inorganic components. A98031

Contrasting effects of productivity and disturbance on plant functional diversity at local and metacommunity scales

“…a P/S fertilizer). Previous studies from this study site showed that pasture growth responded to the addition of P and S, and that irrigation of fertilized plots strongly increased production (Scott 2000). A recent study (Lalibert e et al 2012b) showed that unfertilized plots were dominated by plants with a conservative nutrient-use strategy, whereas plants with leaf traits associated with rapid growth were more abundant in fertilized plots.…”

“…a P/S fertilizer). Previous studies from this study site showed that pasture growth responded to the addition of P and S, and that irrigation of fertilized plots strongly increased production (Scott ). A recent study (Laliberté et al.…”

Sustainability of New Zealand high‐country pastures under contrasting development inputs. 8. Modelling sheep carrying capacity

“…Only the more closely fitting functions were pursued for the more inclusive analyses (ii, iii, and iv). The fit was also calculated for slightly more than half the data (780 observations) covering the zero fertiliser treatments and fertiliser combinations most likely to be economical (Scott 2000c). The mean deviation (Dev.)…”

Sustainability of New Zealand high‐country pastures under contrasting development inputs. 6. Fertiliser efficiency

“…Previous papers have described the trial designs and fertiliser levels used (Scott 1999), the changes in soil inorganic components after 10 years (Scott 2000a), sheep carrying capacities over 15 years (Scott 2000b), and organic components including pasture response (Scott 2000c). These could be considered as referring to a maintenance phase after an approximately five-year initial pasture development phase.…”

“…These interests have been particularly true for South Island high-country rangeland pastoral farming. The present series of papers attempts to quantify some of these production and sustainability aspects based on two long-running grazing pasture trials under contrasting management inputs of fertiliser and grazing management (Scott 1999(Scott , 2000a(Scott , 2000b(Scott , 2000c(Scott , 2000d.…”