No abstract

Two experiments examining the effect of artificial shade on pasture net herbage accumulation (NHA), botanical composition and soil characteristics were conducted between 1994 and 1999 at Whatawhata Research Centre. Both experiments included a range of shade levels (0-94%) and shade durations (3-12 months per year). Experiment 1 also included a light quality treatment, incorporating a range in the red:far red ratio (0.49-1.00). All three shading factors decreased annual NHA, with the most influential being the level of shade, which accounted for 68% of the variation and reduced NHA by 20-80% compared with open pasture. The second most influential factor was shade duration, which accounted for only 6% of the variation in NHA. Shading also led to changes in pasture botanical composition, most notably a decline in legume content in both experiments. There was no evidence that hairy pasture species (grasses or legumes) had any advantage over glabrous species under shade. At shade levels >60%, herbage nitrogen concentrations were elevated by 0.2 percentage points on a per unit dry weight basis, although reduced pasture A04104;

The effects of varying solution concentrations of manganese (Mn), zinc (Zn), copper (Cu), boron (B), iron (Fe), gallium (Ga) and lanthanum (La) on plant chemical concentrations, plant uptake and plant toxicity were determined in wheat (Triticum aestivum L.) grown in a low ionic strength (2.7 × 10 -3 M solution culture). Increasing the solution concentration of Mn, Zn, Cu, B, Fe, Ga and La increased plant concentrations of that ion. Asymptotic maximum plant concentrations were reached for Zn (10 mg kg DM-1 in the roots), Ga (2 mg kg DM-1 in the tops and 18 mg kg DM -I in the roots) and La (0.4 mg kg DM -1 in the tops and 4 mg kg DM -~ in the roots). Plant ion concentrations were, on average, 3 times higher in the roots than the tops for Mn and Zn, 7 times for Cu, 9 times for Fe, 12 times for Ga and 15 times for La. In contrast, B concentrations were higher in the tops than the roots by, on average, 2 times. The estimated toxicity threshold (plant concentration at which a rapid decrease in yield occurred) in the tops was 0.4 mg g D M -~ for B, 2 for Zn, 0.075 for Cu and 0.09 for La and in the roots 0.2 mg g D M -~ for B, 5 for Zn, 0.3 for Cu and 3 for La. Plant uptake rates of the ions (as estimated by the slope of the relationship between solution ion concentrations and plant ion concentrations) was in the order B < Fe < Mn < La < Zn < Ga < Cu for the tops and B < Mn < Fe < Zn < La < Cu < Ga for the roots. In the roots, the uptake rates of La, Cu and Ga was exceptionally high (> 250 mg kg D M -l #M-1). Plant toxicity was estimated as the reciprocal of the plant concentration that reduced yield by 50% (change in relative yield per mg ion kg DM-t). The plant toxicity of the ions tested was in the order Mn < Zn

There are few records of long-term trends in soil C and N in grazed pasture systems but recent measurements have demonstrated unexplained losses on New Zealand lowlands. To determine whether losses were also occurring in hill country pastures, we analyzed archived soil samples collected between 1983 and 2006 from two slope classes (steep and easy) at the Whatawhata Research Centre. Soils were Ultic Hapludand and Typic Haplohumult on the easy slopes (10-20°), and Typic Haplohumult on the steeper slopes (30-40°). Soil samples (0-75 mm) had been collected from paddocks that were fertilized with six different loading rates of P (ranging from 0 to 100 kg P ha -1 -year -1 since 1985). This range of P loadings allowed us to determine whether P inputs would regulate trends in soil C and N. While there were significant temporal trends in C and N (P \ 0.05), these were not unidirectional and trends were not dependent on P loading rate. On average, soil C initially increased during the first 6 years of the trial at 0.270% C year -1 (1.56 t ha -1 year -1 ) and 0.156% C year -1 (1.06 t ha -1 year -1 ) on easy and steep slopes, respectively. Subsequently, there was no significant trend in soil C on the easy slopes but soil C declined at -0.066% year -1 (0.45 t ha -1 year -1 ) on the steep slopes. Similarly, soil N increased between 1983 and 1989 at 0.025% N year -1 (144 kg ha -1 year -1 ) and 0.012% N year -1 (82 kg ha -1 year -1 ) on easy and steep slopes, respectively. Post-1989, small but significant losses of total N were measured on the steep slopes of 0.004% year -1 (27 kg N ha -1 year -1 ) (P \ 0.05) with no trend on the easy slopes. Two potential causal factors for these decadal-scale patterns were identified, operating via changes in primary productivity. These were lower S inputs from 1989 due to a change in fertilizer type, and a series of relatively dry summers during the 1990s. These significant inter-annual trends in soil C and N complicate attempts to measure long-term changes in soil organic matter associated with land use change and management practices. This study has demonstrated the potential error associated with infrequent soil sampling to determine long-term trends in soil C and N; large gains or losses could have been detected at Whatawhata depending on when sampling started and finished. Understanding these long-term trends in soil organic matter dynamics and driving factors requires more long-term sampling trials.

Summary Tawa ( Beilschmiedia tawa )-dominated forest fragments on farms within the Rotorua Basin were surveyed to quantify the likely recovery processes following exclusion of domestic livestock grazing, using a space-for-time substitution approach. Vegetation structure, plant diversity and soil fertility were measured at 24 sites within 15 forest fragments on six farms, covering a range in time since exclusion from grazing of 1-53 years. The forest fragments were compared with a large area of ungrazed forest in the nearby Lake Okataina Scenic Reserve. As time since exclusion from grazing increased, indigenous plant species diversity increased (up to 30 -35 years); ground fern and epiphyte abundance increased (up to 30 -35 years); tree seedling and sapling numbers, and litter cover also increased (up to 10 -15 years); and overall tree numbers increased, while average tree diameter at breast height and overall tree basal area did not differ significantly. The soil fertility status was highly variable, obscuring clear patterns, although Olsen P status decreased with time since grazing exclusion. Once grazing of forest fragments ceases, significant changes in their diversity, structure and soil characteristics can be expected, which indicate recovery of these plant communities towards the conditions observed in ungrazed forest.