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Combined hood and disk infiltrometer experiments were performed in conjunction with the laboratory measurement of soil water retention to quantify the impact on soil hydraulic properties of a mixed cropping rotation compared with pasture. The two sites were in adjacent fields on the same soil type. One site had been cropped for 2 yr. The other site had been under extensively grazed pasture for 2 yr. Our hypothesis was that the soil structure under the cropped treatment represented an initial stage and the soil structure under the pasture a final stage of a mixed pasture–cropping rotation cycle. The measured data were incorporated into an existing pore‐space evolution model describing the temporal change in the pore‐size distribution. The saturated and near‐saturated hydraulic conductivities of the cropped soil were up to four times higher than those of the pasture soil and the amount of flow‐active macropores were approximately 80% larger under the cropping than under pasture. This can be attributed to the loosening by tillage of the cropped soil before our measurements. The observed high infiltration rates under cropping could indicate that water flow took place between the aggregates rather than through the soil matrix. The lower conductivities and smaller amount of flow‐active pores in the pasture soil than the cropped soil can be seen as a collapse of interaggregate pores after tillage. A reasonable prediction of the pore‐size distribution dynamics resulting from different management practices was only possible when this loss of pores due to collapse was considered. For this purpose, a degradation term describing the time‐dependent loss of macropores after tillage was incorporated in the model.

Environmental concerns over nitrate levels in surface and ground water have led to increased efforts to measure nitrate leaching from farmland. This study compared two methods of measuring leaching (lysimeters versus ceramic suction cups) using 12 soil monolith lysimeters (70 cm deep) containing four replicates of three contrasting New Zealand soils: Gorge silt loam, Mataura sandy loam (both stone-free soils) and Lismore stony silt loam. The ceramic suction cups were installed at 35 cm and 60 cm depths. Urea solution was surface applied at 250 kg N ha , followed by regular weekly irrigation. Nitrate leaching loss was calculated by combining the volume of drainage water collected from each lysimeter with the nitrate concentration in either the lysimeter drainage solution or the solution from the suction cups. Cup samples were taken twice per irrigation/drainage sequence: during irrigation and then immediately after irrigation ceased. No evidence of any difference in nitrate concentration and in cumulative leaching was observed between the first and second cup sampling times. However, there was a large variation in individual values measured by the suction cup samples. There were differences between the cumulative leaching loss measured in the lysimeter drainage and values estimated from the cups in the Gorge and Lismore soils. The cumulative leaching loss, measured from the top cups, bottom cups and lysimeter drainage, was 64, 68 and 54 kg N ha(1 respectively in the Gorge soil, 57, 68 and 62 kg N ha(1 in the Mataura soil and 61, 103 and 99 kg N ha (1 in the Lismore soil. It was concluded that suction cups were inappropriate for the determination of cumulative leaching in the structured Gorge soil and the Lismore topsoil, but ceramic cups could provide useful data on cumulative leaching in the Mataura sandy loam soil. It was hypothesised that preferential flow was likely to be the cause of the differences between the results obtained from suction cups and the lysimeter drainage, especially in the Lismore and possibly the Gorge soils, where the small sampler size was not able to capture a representative sample of the pore network responsible for the soil drainage.

In New Zealand, occurrence of loess often determines the spatial pattern of soil depth, and influences droughtiness, leaching potential, organic matter accumulation, nutrient retention, and natural plant-species distribution. Understanding loess distribution is therefore a major prerequisite for soil and land resource management. Although New Zealand's soil scientists have accumulated a good empirical knowledge of loess distribution through several decades of field investigation, only some of this knowledge is recorded in papers and reports. This study estimates loess thickness and percent cover, and provides loess landscape models for the internal loess distribution of all land units in the South Island based on expert knowledge. We derived loess depth classes and percent cover classes and assembled land units with similar loess distribution patterns. The soil sets underpinning the map units of the New Zealand Land Resource Inventory (NZLRI) were classified according to loess depth, loess cover, and loess pattern. New loess maps of the South Island were produced from those classifications, displaying loess coverage, thickness, loess pattern, and loess landscapes. These maps present our current knowledge of the coarse-scale loess distribution and provide a framework for fine-scale loess landscape modelling.

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