A boroscope and mini-rhizotrons were used to explore root growth patterns in five different ryegrasses grown outdoors under simulated field edaphic conditions including drought. Few major differences in root counts were found among the ryegrasses. The seasonal patterns of root counts in well-watered treatments showed an autumn peak that was later (or even suppressed) as autumn soil temperatures increased in consecutive years. Seasonal patterns were not measurable at more than 7 cm depth down the profile. The summer drought resulted in an increase in root counts right down the profile, which started about a month after the drought began. This was followed by rapid death of roots in the top 15 cm of soil but lower death rates deeper in the soil. After rewetting of the soil, there was a delay of approximately 1 month before a rapid increase in root production occurred. This overcame the apparent high soil temperature inhibition of autumn root growth in the well-watered control treatment.
A small-plot field experiment on grazed hill country pastures in the North Island of New Zealand was conducted to examine the productivity and compositional characteristics of swards in response to variation in pasture species diversity. The balanced incomplete factorial design incorporated variation in location, slope, soil fertility and combinations of eight plant functional groups (C 4 grasses, annual grasses, annual legumes, perennial C 3 grasses, perennial legumes, perennial forbs, ryegrass and browntop). Net herbage accumulation and botanical composition were measured at 18 months (spring) and 24 months (autumn) after oversowing following application of a systemic herbicide. Analysis of variance indicated a significant positive relationship between the number of functional groups sown and herbage accumulation of the sown species in spring, but not with total herbage accumulation. Regression analysis showed that herbage accumulation was also affected by the identity of the functional groups. However, the statistical models indicated that pasture productivity was most strongly influenced by site factors. There was a significant negative relationship between both the number and herbage accumulation of unsown species and the number of functional groups sown, indicating a positive relationship between diversity and resistance to invasion by unsown species. A comparison of the vegetation between the plots before and after oversowing showed that those more diverse prior to sowing returned to their initial composition more rapidly, evidence that diverse vegetation was more resilient in the face of disturbance.
The third phase of a multi-stakeholder, integrated catchment management project at the Whatawhata Research Centre is described. Land use and management changes were implemented to improve economic and environmental performance of the Mangaotama case study catchment farm. The major changes included: afforestation of 160 of the 296 ha catchment farm with pine and native trees, riparian management of the entire 20 km of stream network via fencing and/or forestry, restoration of 5 ha of existing native forest, and intensification of the remaining pastoral component to a high fecundity ewe flock and bull beef finishing. Marked improvements were observed in the key environmental and economic performance indicators. In particular, declines in sediment (76%) and phosphorus (62%) loads and faecal coliform (43%) levels were observed, native forest fragments showed early signs of recovery in terms of sapling numbers and vegetative cover, and the pastoral enterprise recorded increased per hectare production of lamb (87%) and beef (170%). There were implementation challenges with the better matching of land use to land capability, but this study demonstrated that significant progress can be made in the short-term.
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