Abstract
Results are reported of the residual effect of North African finely ground rock phosphate and superphosphate in two field trials on acid fine sand and humus soils. During the first seven years of these trials 166 kg P/ha was applied either as rock phosphate or as superphosphate to cereals and mixed leys. Then crops were grown for three years without any application of phosphorus fertilizers. The phosphorus analyses of the soil at the end of the seventh experimental year proved that the largest part of rock phosphate occurred in the acid soluble fraction, probably mainly as unweathered apatite. The superphosphate phosphorus seemed to be accumulated as fluoride-soluble and alkali-soluble forms. In the trial on the humus soil of a fairly high productivity, the residual effect of both fertilizers on three oat crops was insignificant. In the trial on the poorer fine sand soil, the residues of both fertilizers produced significant and mutually equal increases in the dry matter yields of the oat crop in the first year and of the hay crops in the second and third years. The tendency to a higher phosphorus content in the graminaceous plants from the superphosphate plots resulted in a higher uptake of phosphorus from these plots as compared with the phosphorus yield from the rock phosphate plots; only in the third year the difference was no more significant. Attention was paid to the good capacity of red clover to use phosphorus of rock phosphate.
Highlights
In 1954 two field trials were started in Central Finland by the head at that time of the local agricultural experiment station, the late Dr Pentti Hänninen, to compare the response of cereals and ley plants to finely ground North African rock phosphate (Hyperphosphate) and superphosphate
The initial response of crops to apatite of rock phosphate is in most cases lower than that to the readily soluble monocalciumphosphate of superphosphate, but the gradual release ofphosphorus from the former, and the immobilization of the latter will often result in an equal residual effect of these fertilizers
This kind of observations have been reported by several authors (e.g. Moschler et al 1957, Tainio 1958, McLachlen 1960, Mattingly 1963), and the results of trial K 104 are in accordance with this view, if only the dry matter yields are compared
Summary
In 1954 two field trials were started in Central Finland by the head at that time of the local agricultural experiment station, the late Dr Pentti Hänninen, to compare the response of cereals and ley plants to finely ground North African rock phosphate (Hyperphosphate) and superphosphate. In Finland, usually, about twice as much phosphorus as hyperphosphate than as superphosphate is needed for the production of equal increases in dry matter yields. In these trials, from the third to the sixth test crops, repeated application of equal amounts of phosphorus either as rock phosphate or as superphosphate gave the same response in the dry matter yields, but, at least in the red clover-timothy ley of 1959, the phosphorus content of the hay from the rock phosphate plots was distinctly lower than that from the superphosphate plots, mainly because of the poor uptake ofapatite phosphorus by grasses (Kaila and Hänninen 1960). The primary yield results and the samples were provided by Dr Hänninen; the analytical work has been done by the author
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