Extensive M.A.F. study of phosphatic fertilisers

Press, 11 February 1983, Page 22

Extensive M.A.F. study of phosphatic fertilisers

A major national series of trials on the effectiveness of present and future phosphatic fertilisers has been launched by the Ministry of Agriculture and Fisheries.

The series will seek information on the cost effectiveness of different phosphatic fertilisers under maintenance topdressing and on established pasture. Soil types and climatic conditions will also be considered. This is the first national series of trials comparing a wide range of phosphatic fertilisers. Other research of this nature in the past has concentrated on establishing rates of application for superphosphate, or compared commercially produced superphosphate with monocalcium phosphate, the main active ingredient in super. The co-ordinator for the new series. Dr Bert Quin, a technical adviser with the Research Division, said there was pressure from farmers and fertiliser manufacturers for more wide-ranging research into and possible new phosphatic fertilisers, so that more information could be available to the whole industry. Many alternatives to superphosphate existed which could get the nutrients on the ground for the same cost as the established basic fertiliser, but information on the cost effectiveness of these alternatives as maintenance

fertilisers was needed. Until recently superphosphate was so cheap that extensive information about the alternatives was not considered necessary. The trials will be set up at 22 or more sites throughout New Zealand, including irrigated and non-irrigated land at the Winchmore Research Station. Mid-Canterbury, and on the West Coast. The trials will be controlled by an M.A.F. scientist in each area and will probably occupy 10 to 20 per cent of each scientist’s time. The trials will not be grazed. Measurements will be taken of' dry matter yield, and herbage phosphate and some very detailed analyses of soil chemicals carried out.

The initial procedure will be to establish response curves to phosphatic fertilisers at each site. For this purpose triple superphosphate and Peruvian reactive rock will be used. The triple super is being used to establish standard response curves because it has the highest proportion of water-soluble phosphate, and not because it is necessarily the best product for the’future. Peruvian reactive rock is being used because it can be spread as received into the country without further refining. Both products will be spread at a range of rates to construct response curves representative of each trial site.

The next phase of the trial series will be to spread other phosphatic fertilisers, at a single rate; and match their response against the predetermined curves. Cost-effectiveness information is arrived at by comparing individual response curves against those generated from the multiple rate applications of triple superphosphate and Peruvian reactive rock. Other fertilisers to be compared include: • High-quality superphosphate made under controlled conditions using Nauru rock — supposedly the best super possible. • Superphosphate made from 50:50 Nauru and Christmas rock under controlled conditions. • Commercially made super from the same blend. • The local commercially available superphosphate. • A mixture of 50:50 super and reactive rock. • Reactive rock sprayed with sulphur. • Reactive rock, from North Carolina, finely ground and made into granules. • Whatever the local scientist wants to include. Dr Quin said results from some facets of the trials would begin appearing by the end of the autumn but as the main purpose was to establish cost-effectiveness under maintenance applications, the whole series could

take three to five years to complete. Results would be published as they came to hand and also be included in the M.A.F.'s new fertiliser recommendation system. He stressed that the scientists in each of the regions would be responsible for interpretation of results and that his own role was mostly co-ordination. A useful by-product of the trial series would be information on the effectiveness of possible new soil phosphate tests. The scale of the series and its emphasis on the large number of trial sites indicates the importance with which the M.A. F. views continuing research into phosphatic fertilisers. "We need to get an overview of different fertilisers on different soil types so that our advice to farmers will be as full and as accurate as possible.” said Dr Quin. “Next to interest on borrowed money, fertiliser is the largest single item of expenditure on farms. Therefore we have to ensure the cost-effectiveness of the various fertilisers available."