A comparison of dicalcium phosphate and single superphosphate as phosphate sources for pasture

Abstract

The effect of commercially available dicalcium phosphate (DCP) and single superphosphate on pasture production was evaluated in glasshouse and field trials. When compared on a unit-P basis, DCP (5.6% P) was slightly inferior (up to 10%) to superphosphate (8.6% P) in a glasshouse trial with ryegrass as the indicator plant; on a unit weight basis, DCP was only 60-70% as effective as superphosphate. No differences were obtained in the P concentration of the herbage obtained using the two materials. In a field trial on a P-responsive site, DCP and superphosphate gave similar increases in pasture production. Marked treatment differences were obtained for the P concentrations in ryegrass and clover in the field trial, particularly in the first harvest and with ryegrass. No difference was obtained in the short-term residual effect of the two materials. The data obtained are interpreted in terms of the chemical and mineralogical composition, and water solubility of DCP.

Effect of lime and form of superphosphate on productivity of dryland pastures

“…For the P effect, this result is consistent with overseas (Cooke 1956;Mattingly & Penny 1968) and New Zealand (Mackay et al 1980) evidence. Although Mackay et al (1980) reported an initial higher P concentration in ryegrass from superphosphate compared with dicalcic soon after application, this difference diminished with time. In this trial, there were no differences in P concentration between dicalcic and superphosphate, although no plant chemical concentrations were measured in the first three harvests.…”

“…It has been used as a P fertiliser mainly on the east coast of the North Island but currently accounts for less than 10% of the applied P fertiliser. Previous research has shown that dicalcic is inferior to superphosphate when applied at the same rate (Cooke 1956;Mattingly & Penny 1968;Mackay et al 1980) but has similar effectiveness to superphosphate (Mackay et al 1980) on a per kg P basis.…”

Changes in phosphorus turnover when soils under long-term P management are amended with bio-based fertiliser

“…This can be associated with different P solubility of each fertiliser. For instance, while 70 % of TP in form of inorganic soluble phosphates (Mackay et al, 2012), chemically treated bio based fertilisers generally have smaller fraction of soluble P due to elevated concentrations of P precipitating metals (Kratz & Schnug, 2010;Möller et al, 2018;Shi et al, 2021;Wollmann et al, 2018) , and potentially need to undergo an intermediate step of solubilisation of precipitated and mineralization of organic P. Therefore contribution of biotic P influx remain consistently high in P deficient and optimal P soils amended with DPS and only decreases in excess P soil, which had no P limitation in the rapidly exchangeable and available P pool even prior to DPS application.…”