A simulated rainfall study carried out as part of a larger grazing experiment was conducted to investigate the effects of a 2-3 day cattle-treading event in winter on soil physical properties and contaminant (sediment and nutrient) runoff in topographically variable hill land. Measurements were made on two land zones: easy contoured ridges and gullies (15-24° slope) and steep inter-track land (28-39° slope). Simulated rainfall was applied to 16 plots (0.5 m 2 ) with a range of treading damage for each land zone within 14 days of the treading event. Simulated rainfall was repeated on the same plots in the following summer and winter to assess the recovery of soil from treading damage. A97034 Received 28 April 1997; accepted 22 January 1998Treading damage reduced water infiltration rate, particularly in the steep zone. It also caused a significant increase in the transport of suspended solids (SS), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) from the plots during simulated runoff. On the steep inter-track zone, damaged areas had a 46% lower infiltration rate, and runoff from these areas contained on average 87% more sediment, and 89% more N and 94% more P compared with undamaged areas. These effects had disappeared six months later. The rainfall simulation and soil physical studies show that a 2-3 day winter treading event may increase soil bulk density, reduce soil macroporosity and total porosity, and lead to a decrease in the water infiltration rate and an increase in contaminant runoff.

An experiment was conducted on steep hill land in New Zealand to describe the pattern of cattle treading that occurred from a single damage event during winter. The experiment also measured some of the consequences of treading and sought to define the subsequent grazing management which promoted the most rapid recovery of pasture.In hill paddocks of mixed topography, damage of the soil surface was greatest on animal tracks/ camps and easy contoured areas (<25°) where cattle prefer to walk. Evidence of this initial winter impact disappeared over spring, most rapidly on easy contoured areas and under continuous sheep grazing. To promote rapid recovery of damaged paddocks continued grazing of cattle during spring should be avoided.At high levels of damage (>50% soil surface), puddling on tracks/camps and skid damage on steep inter-tracks became frequent. These processes are significant because animal tracks/camps act as important channels for surface water flow in hill lands; and disturbed, inter-track areas are an important source of sediment runoff.During spring, pasture growth rates were reduced by treading damage. From a systems context this could represent losses of 5-10 kg DM ha -1 d -1 during early-mid spring. Pasture cover and growth rates had fully recovered by early December.

Aspect and land slope have a major influence on winter and spring pasture growth. Possible physiographic, soil, and plant factors contributing directly to this influence were examined across a range of microsites in steep North Island hill country. As land slope increased, organic and inorganic nitrogen in the soil decreased. Similarly, organic carbon decreased and this was associated with a decline in soil water-holding capacity. Soil water potentials were high during winter and spring and showed little effect of aspect. Pasture growth was greater on warmer, north-facing than on colder, south-facing aspects, the difference being less for ryegrass-dominant sites than for browntop associations. Where long-term site conditions (e.g., slope, fertility, moisture) allow the development and maintenance of perennial rye grass populations, greater winter and spring growth rates were recorded. The importance of developing an effective N cycle based on stable legume populations for improving soil N status, ryegrass content, and cool-season pasture production in hill country is highlighted.

Nine subterranean clover cultivars and 11 white clover lines were evaluated for persistence and production, under a combination of rotational grazing or cutting, for 4 years on rolling pumice hill country. The most successful subterranean clover cultivarwas 'Tallarook' , whichfor 4 yearsproduced the most dry matter (DM) (average 700 kg DM/ha per year) and accumulated the largest soil seed reserve (1500 kg seed/ha), Soil moisture stress over the summer severely limited persistence and hence production of all white clovers (average 400 kg DM/ha per year). Persistence was not assured by larger roots associated with large-leaved lines. Hill country types (e.g., 'Whatawhata Early Flowering') with a high stolon densityand/or free seedingability were the best adapted to this environment

Subterranean clover and white clover plant material was collected from 85 sites located in summerdry northern North Island hill country. Plants of both species originating from this collection were grown and typed at Whatwhata Hill Country Research Station. Using several cultivars and selections as standards, measurements were made of morphological, flowering and reseeding characteristics. The subterranean clover population consisted of 44% Mt Barker type, 28% Tallarook type and the remainder an undetermined intermediate type. Mt Barker types in the collection tended to flower later and for longer than their Mt Barker standard, while Tallarook types tended to flower earlier and for longer than StandardTallarook. White clover plants were smaller and more densely leaved than 'Grasslands Huia', the population mean being similar to 'Grasslands Tahora'. A vast majority (7035%) of plants flowered earlier and yielded more seed than Huia and Tahora. An apparent shift in plant type has occurred within clover populations in summerdry hill country, the most notable being the development of a more flexible reseeding pattern. This type can be a future guide to breeding clovers suitable to these environment . Keywords: white clover, subterranean clover, flowering, seeding, morphology, type hill country