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The influence of four cultivation treatments viz ploughing rotary hoeing power harrowing and no soil disturbance on the distribution of weed seeds in the soil profile was investigated in a field trial Weed seeds were counted by dry sieving soil samples collected from 05 510 1015 and 1520 cm depths The density and species of weeds that emerged in field plots were also recorded at threeweekly intervals Samples from undisturbed plots showed a linear decline with depth Ploughing was the only treatment that caused a significant shift of seeds to the deeper profile Ploughed plots had significantly fewer weed seedlings than other treatments due to lower numbers of both summer grasses and broadleaf weeds Undisturbed plots contained significantly fewer broadleaf species and weed emergence was delayed Implications of these results for seedbank sampling methodology and weed management strategies are discussed

The effect of cultivation on spider density and diversity was assessed at three sites before and after cultivation in autumn. Linyphiid spiders dominated the fauna at each site (60-90% of the spiders present) with Eperigone fradeorum (Berland) the most common spider (38% of the spiders collected). At all three sites, the populations of both linyphiid and non-linyphiid spiders decreased significantly after fields were cultivated. Population declines after cultivation did not appear to be related to the intensity of cultivation. This suggests that environmental factors were not an important influence on spider populations, at least in the early part of the experiment. Grazing had a detrimental effect on spider density and diversity. These results suggest that both cultivation and ongoing management can affect spider density and diversity.

The relationship between laboratory enumerations of the weed seedbank and field populations of major grass weeds was studied in several maize fields over a three year period. After planting the crop, 1 m 2 areas were protected from the pre-emergence herbicide application. Soil samples were collected soon after spraying from each area to a depth of 100 mm, and the seeds of the major grass weeds enumerated at a seed testing laboratory. Emerged weed seedlings were counted in each sampling area over the following 8 weeks. Grasses present at these sites included: summer grass (Digitaria sanguinalis), smooth witchgrass (Panicum dichotomiflorum), barnyard grass (Echinochloa crus-galli) and rough bristle grass (Setaria verticillata). On average 6-12% of the seed in the soil seedbank emerged in any one year depending on species. Significant linear relationships were established between seed numbers in the soil and the seedlings that emerged in the field.

The effect of early weed competition was determined for a maize (Zea mays) crop grown in Waikato Maize was established in three different environments viz weedy (no herbicide) grass weeds (preemergence atrazine) and broadleaf weeds (preemergence metolachlor) Surviving weeds were controlled with postemergence nicosulfuron (60 g/ha) after different periods of competition and the plots kept weed free for the remainder of the trial Weeds left completely uncontrolled for 4 weeks after emergence significantly reduced crop yields When a preemergence herbicide was used surviving weeds began to reduce maize yields after about 6 weeks with grasses having greater effect than broadleaf weeds The actual period before the weeds started affecting crop growth and yield appeared to be related to the time taken by the weeds to achieve complete ground cover