Growth and yield of sugarcane as a function of phosphorus doses and forms of application

ABSTRACT This study aimed to evaluate sugarcane growth and its agricultural and industrial yield influenced by phosphorus (P) sources and forms of application. The experiment was carried out at the Paisa Sugar Mill, in Penedo-AL, Brazil, from February 2012 to February 2013. The adopted experimental design was a randomized block in a factorial arrangement, with four replicates. The treatments consisted of five doses of triple superphosphate applied in the planting furrow (0, 50, 100, 150 and 200 kg ha-1 of P2O5), and three doses of Bayóvar reactive phosphate rock (0, 100 and 200 kg ha-1 of P2O5) applied in the total area. Phosphorus applied in the planting furrow improved sugarcane quality through the reduction of fiber and increases in purity, corrected pol, total recoverable sugar, ton of pol per hectare (TPH) and ton of sugarcane per hectare (TSH). The Bayóvar reactive phosphate rock promoted increases in stem diameter at 120 days after planting (DAP), TPH and TSH. For the interaction triple superphosphate applied in the planting furrow x Bayóvar reactive phosphate rock applied in the total area, there were significant differences in the number of tillers at 30 DAP, stem diameter at 120 DAP and TSH.

RPR revisited (2): Long-term farmer experience helps define the role of RPR in grazed pastures

The commercial introduction of reactive phosphate rock (RPR) to the New Zealand market in 1987 was the subject of much dispute regarding its efficacy, and the differing interpretations of field trial results. Twenty-five years on, it was considered time to seek the views of farmers who are long-term users of RPR, across a wide range of geographic, soil type, fertility, climate and farming operations. The fact that the farmers interviewed have all been farming successfully with RPR for many years enables conditions suitable for RPR use to be identified more clearly compared to earlier advice. This progress is discussed in the context of utilising the proven reduced phosphorus (P) run-off with RPR to reduce P eutrophication in P-sensitive catchments. Key words: Reactive phosphate rock, RPR, superphosphate, SSP, long-term use, phosphorus runoff, eutrophication, water quality, recommendations

RPR revisited (1): Research, recommendations, promotion and use in New Zealand

Reactive phosphate rock (RPR) has been studied extensively in field trials and laboratory research in New Zealand since the 1930s. This paper looks at the different approaches to research over the decades, at what conclusions were drawn, at the recommendations made to farmers, and at the commercial promotion and sales of RPR. It is not an exhaustive literature review, but sufficiently comprehensive to demonstrate the large amount of research conducted, and to document the important issues that have arisen, particularly with respect to advice being given to farmers. RPR research has suffered from a series of mishaps which have hindered, in one way or another, the results being accurately interpreted and passed on clearly to farmers. There is a need for specific advice for farmers regarding managing or minimising any lag in production following a switch to RPR. New Zealand's grazed pastures, water quality and "clean and green" image internationally are closely interlinked. Given the proven significant reduction in P losses in run-off to waterways with RPR, the conditions in which RPR can be successfully used in New Zealand's pastoral agriculture have been reassessed. Key words: reactive phosphate rock, RPR, superphosphate, SSP, TSP, PAPR, long-term comparisons, plot trials, grazing trials, fertiliser recommendations, history

Phosphorus management on extensive organic and low-input farms

A synthesis of the Australian literature reporting soil and plant phosphorus (P) status under organic methods of broadacre farming provides clear evidence that available soil P is lower in organic systems, although there have been no reports of farm P balances that might help to explain the lower P concentrations. There is also evidence, which is largely circumstantial, to suggest that P deficiency significantly reduces productivity of broadacre organic farms, but few experiments prove this conclusively because of other confounding factors. An overview of international literature suggests similar findings for mixed farms. Nine case studies further examined the constraints imposed by P on broadacre organic and low-input farms in Australia. Two farms on fertile soils had negative P balances but maintained productivity without fertilisers by ‘mining available’ P reserves. Five extensive organic farms on inherently less fertile soils had positive P balances because P fertiliser was used. Four of these farmers reported low productivity, which was supported by comparisons of wheat yields with estimated water-limited potential yields. Low productivity appeared to be related to P deficiency despite the use of allowable mineral fertilisers, mostly reactive phosphate rock (RPR), on these farms. The apparent ineffectiveness of RPR is most likely due to the modest rainfall at these farms (380–580 mm/year). The highest research priority is to develop effective, allowable fertilisers. Until this has been achieved, or ways of using less labile P have been developed, there is a case for derogation in the Certification Standards to allow the use of soluble forms of P fertiliser on soils with low soil solution P and high soil P-sorption. Two low-input farms practicing pasture-cropping had approximately balanced P budgets and from this perspective were the most sustainable of the farms studied.