Atmospheric nitrogen (N) deposition alters plant biodiversity and ecosystem function in grasslands worldwide. This study examines the impact of 6 years of nutrient addition and grazing management on a sand dune grassland. Results indicate that co-limitation of N and phosphorus (P) moderates the impact of realistic rates of N addition (7.5, 15 kg N ha −1 year −1 ). Combined NP addition (15 kg N + 10 kg P ha −1 year −1 ) was the only nutrient treatment to differ significantly from the control, with greater above-ground biomass (mainly moss), and enhanced N and P mineralisation rates. Grazing management altered plant functional group composition, reduced above-ground biomass and meso-faunal feeding rates, and decoupled N and P mineralisation. There were no synergistic effects of grazing and N treatment. Although NP co-limitation apparently prevents adverse impacts of N deposition above the critical load, excess N is likely to be stored in moss biomass and soil, with unknown future consequences.Capsule: This study shows that at realistic levels of N addition, NP co-limitation in a dune grassland appears to prevent adverse impacts of N on plant growth and nutrient cycling.
Mowing trials were carried out to determine the rates of fertiliser nitrogen (N), phosphorus (P), potassium (K) and sulphur (S) and frequency of application of K for maximum pasture production on extremely infertile humped and hollowed pakihi soils in the Grey Valley (Souters and Sommervilles dairy units), and flipped soils at Cape Foulwind (Bassetts dairy unit) under high annual rainfall (2000 - 3000 mm) on the West Coast. In the first measurement year, there was no significant increase in pasture production above 480 kg N/ha, 56 kg P/ha, 360 kg K/ha and 136 kg S/ha at Souters and Bassetts and a significant increase in pasture production up to 600 kg N/ha, 56 kg P/ha, 360 kg K/ha and 140 kg S/ha at Sommervilles. In the second year, there was no significant pasture production increase above 480 kg N/ ha, 56 kg P/ha, 360 kg K/ha and 136 kg S/ha at all sites. The high N, K and S rates were required because nutrients were not being recycled through returned clippings. This situation would be similar to the early stages of dairy management on these units where only a small proportion of pasture would receive recycled nutrients through return of excreta. Over time, a larger proportion of the pasture would be affected by excreta and fertiliser nutrient requirements would be expected to decrease. There was no increase in pasture production from applying potassium chloride in more than four applications per year at Souters and Bassetts in the first year, but a significant increase in pasture production from eight compared with four applications per year at Sommervilles, where soil QT (quick test) K levels were lower than at the other two sites. Keywords: flipped, hump and hollowed, nitrogen, phosphorus, potassium, sulphur
Inadequate pasture growth from September to November has been a major constraint on animal production at Limestone Downs, Port Waikato. In an attempt to address this, urea was applied by air in two applications per year (late autumn + winter) at rates up to 250 kg N/ha/year for each of 3 years (2004-2007). Key words: nitrogen, slope, aspect, pasture growth, fertiliser response
This review paper discusses aspects of hill country science-based soil fertility management advice given to farmers in the past on the use of fertiliser, principally superphosphate, on hill country farms. This shows that both pasture quantity and quality are improved with the application of the nutrients phosphorus (P) and sulphur (S) in superphosphate and that an unseen benefit of this is the increased food supply to soil biological organisms which also flourish under this management. The large potential for nitrogen (N) fertiliser application is explored and demonstrated. New thinking and technologies are allowing farmers to differentially apply variable rates and types of fertiliser nutrients by air to better match the growth potentials of contrasting hill country zones and so ensure that the investment in fertiliser will give the best financial returns possible. Keywords: soil fertility, hill country, differential application, variable rate
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