Incidental phosphorus loss is a concern for surface water quality. Here we showed that the risk of incidental P loss can be minimised, even from highly soluble superphosphate fertiliser, by timing application when overland flow is unlikely. Moreover, we demonstrated that the risk of incidental P loss can be estimated from water solubility, decreasing the need for expensive field trials. As such, we suggest that slowly available fertilisers such as reactive phosphate rock or serpentine super could be used in situations where incidental losses need to be decreased and conditions are suitable e.g., soil pH less than 6 and rainfall greater than 800 mm for reactive phosphate rock.

Fertiliser management is an important aspect of growing good forage brassica crops. Every crop has a different requirement, depending on soil fertility and the expected yield response. Systems were developed for forecasting how much fertiliser, and what types, to apply to individual kale and Pasja crops. First, yield responses to fertiliser application were measured in trials in diverse climates and soil fertility conditions. Yield responded strongly to N and P availability, there were few responses to K fertiliser application, and there were no responses to S application. Second, overall responses to the nutrient supply from soil and fertiliser sources were determined in a comprehensive across-trials analysis using the PARJIB model. R-squared values for correlations between actual yields and yields simulated with the PARJIB calibrations were 0.65 and 0.64 for Pasja and kale respectively. Finally, the results were programmed into new software systems (The Kale Calculator and The Pasja Calculator) that deliver a forecast for each crop of the types and amounts of fertiliser that will give the best economic return on the investment in fertiliser. Keywords: The Kale Calculator, The Pasja Calculator, fertiliser application, yield response, PARJIB analysis

No abstract

The trial reported here investigated the effect of applying dicyandiamide (DCD) in a granular form on N 2 O emissions in a grazed pasture system over 2 years. In 2004, treatments of urea or urea + zeolite-DCD were applied randomly to pairs of plots following grazing in late autumn. Both treatments received urea at a rate of 50 kg N ha -1 , while the latter treatment also included an application of granular zeolite/DCD at 42 kg ha -1 (DCn™: 10 kg ha -1 DCD). In 2005, the same treatments were applied following grazing in early and late autumn and early spring. Measurements of N 2 O emissions were made at frequent intervals following treatment application using a standardised soil cover technique. Large variability in N 2 O emissions and soil mineral N levels were measured, due to the variable nature of urine N return by grazing animals. Nevertheless, the results clearly showed that the granular zeolite/DCD significantly reduced N 2 O emissions from grazed pasture from 1.0 to 0.3 kg N ha -1 , 3.7 to 0.7 kg N ha -1 and 2.9 to 0.3 kg N ha -1 for the three measurement periods.This equates to reductions of between 75 and 90% over a 2-to 3-month measurement period. Based on these results, and the assumption that 40-50% of annual N 2 O emissions occur during the times when nitrification inhibitor application is recommended, granular zeolite/DCD reduced annual N 2 O emission from grazed pastures by 30-45%.

In pastoral dairy grazing systems, the high localised nitrogen (N) concentration in urine patches has been identified as a major source of nitrate nitrogen (NO 3 -N) available for leaching. Our study was initiated to investigate the effectiveness of different formulations of a nitrification inhibitor, dicyandiamide (DCD), in limiting NO 3 -N accumulation in a typical Southland pastoral soil. Various formulations of DCD (Super U, DCD-urea granules, DCD in zoelite granules and DCD in solution), both in the presence and absence of artificial urine, were applied to small plots in late October 2003. With the exception of Super U, all the DCD formulations evaluated were effective in limiting the nitrification of ammonium-nitrogen (NH 4 -N) to NO 3 -N in soil for in excess of 100 days. Thus, applying DCD in a granular form or in conjunction with granular fertiliser can be an effective way to limit NO 3 -N build-up in the soil profile. Total pasture production over the duration of the trial was increased by the DCD application in the N-fertilised treatments by between 8 and 21%, but no significant differences in pasture production were noted for treatments that included an application of artificial urine. The DCD application had the added benefit of limiting nitrate accumulation in the herbage to safe levels for ingestion by grazing animals, as well as a trend to increase herbage magnesium (Mg) and calcium (Ca) concentrations, so counteracting the possible detrimental effects of high potassium (K) concentrations where urine had been applied to a Southland pastoral soil.