DAP slurry evaluations in Hawke's Bay

Abstract

Three experiments were conducted in Hawke's Bay to evaluate the agronomic effectiveness of DAF' slurry fertilisers containing finely ground diammonium phosphate (DAP). The experiments also compared the effectiveness of sulphur (S) applied as sulphate and as elemental S. Experimental sites, all on dryland yellow-grey earth soils on permanent sheep pasture which had not received fertiliser for several years, covered a range of soil fertility, pasture species and chemical composition. Trials were open to grazing, and exclusion cages were used to measure herbage production over 1 or 2 years. No difference in yield (PrO.05) was recorded for DAP applied at low rates either as a slurry or as a conventional solid fertiliser. It was concluded that grinding of DAP into small particles and its application as a slurry had no effect on the agronomic performance of the applied nutrients when compared with solid fertiliser. DAP slurry fertilisers had no statistically significant effect on herbage dry matter production, dry matter digestibility, protein content, or trace element content relative to unfertilised control pasture. Application of DAP slurry twice at annual intervals had no significant (PrO.05) effect on soil test measurements. Sulphate S was more effective than elemental S in overcoming S deficiency in these experiments. Keywords: diammonium phosphate, fertilisers, fertiliser forms, Hawke's Bay, slurry fertilisers, sulphur