Aspect differences in an unimproved hill country pasture

Abstract

A number of climatic variables were monitored on north, south, east, and west aspects of a hill in the foothills of the southern Ruahine Range, New Zealand, over a 12-month period. Wind speed values were consistently higher on the north aspect than on the west, east, and south aspects. Differences in net radiation between the north and south aspects were largest during the winter and smallest during the summer months. All evapotranspiration values calculated were larger for the north than for the south aspect. Soil moisture tension differences were not detected during winter, but during the remainder of the year soil of the north aspect had the highest moisture tension and that of the south aspect the lowest. Rainfall differences among aspects were difficult to detect because of the effects cf wind on rain gauge catch. Differences among aspects in average monthly 40 mm air temperature were not appa-rent. However, large differences in the average monthly 40 mm soil temperature of the various aspects were detected. During the Tanuary to August period the north aspect was warmest and the south aspect coolest, but for the remainder of the year the east aspect was warmest. The interrelationships of some of the above variables are discussed. It is suggested that the significance of wind in the hill pasture environment is underestimated.

Towards an improved understanding of the soil water balance of sloping land under pasture

“…For land under pasture at Taita near Wellington, Jackson obtained evaporation estimates of 904 mm and 584 mm for 308 N and S facing slopes respectively, for the year 1966. Lambert & Roberts (1976) obtained similar differences for 148 N and S facing slopes near Palmerston North, suggesting that different evaporation rates were the reason for the often different moisture conditions they observed in N and S aspect topsoil.…”

“…evaporation, rainfall, runoff, drainage and DM yield) are expressed on a horizontal projection basis, as that is the way land area is mapped and rainfall measured. Lambert & Roberts (1976) and Bircham & Gillingham (1986) do not specify whether the values they give are per unit slope area or per unit horizontal projection. For a 308 slope there is a 15% difference between the two values.…”

“…Both Radcliffe (1968) on Banks Peninsula in Canterbury and Gillingham (1974) at Whatawhata in Waikato used soil sampling to show that the top 75 mm of soils on north (N) facing slopes were significantly drier than those on south (S) facing slopes. Lambert & Roberts (1976) using gypsum blocks found that the soil on a N facing slope was often at a lower matric potential (and so drier) than the soil on a S facing slope in hill country near Palmerston North. Jackson (1967) used the Penman equation to estimate the effect on reference crop evaporation (or what was referred to then as the potential evapotranspiration) of the varying amounts of solar radiation falling on slopes of differing aspect and steepness.…”

Establishment of ryegrass, cocksfoot, and white clover by oversowing in hill country 2. Sown species and total herbage accumulation

“…Firstly, this experiment was confined to one stratum within a highly heterogeneous environment. Pasture performance on drier north or north-west aspects may benefit more from the introduction of cocksfoot particularly, as they are more prone to moisture stress than easterly aspects (Lambert & Roberts 1976). Secondly, heterogeneity on a finer scale introduces considerable variability in data collected from experiments of this nature (coefficients of variation for total herbage accumulation in seasons averaged 36.8%), even when efforts are made to choose relatively uniform plot sites as in this trial.…”

Plant available potassium in New Zealand steep-land pasture soils

“…Most (96%) of the soil samples collected from this area had relatively high Step K values. In New Zealand, the soils on a slope of northerly aspect, like this one, are generally warmer and drier (Gillingham, 1974;Lambert and Roberts, 1976). Such soils are therefore expected to be less weathered, because they are less leached (Churchman, 1980;Muhs et al, 2001).…”