Rit Landbúnaðardeildar : B-flokkur - 01.12.1961, Blaðsíða 32

Abstract:
THE UTILIZATION OF PHOSPHORUS
IN POT EXPERIMENTS AND FIELD TRIALS
I. PHOSPHORUS IJPTAKE BY GRASS GROWN IN MITSCHERLICH POTS.
Experimental.
In 1954 and 1955 fertilizer trials were initiated, using Mitscherlich pots, 20 cm in diameter
and 18 cm high (see figure). Table 1 lists some characteristics of the soils used for the
experiments in question. The test plant grown was timothy, variety Engmo, from Norway. Fer-
tilizer materials were applied in solution, nitrogen as ammonium nitrate, phosphorus as mono-
calcum phosphate, and potash as potassium chloride. In all pots dealt with in this paper, the
amount of nitrogen and potash remained constant, corresponding to 150 kg N and 100 kg K2O
per hectare. In some of the pots, lime (calcium carbonate) was mixed uniformly through the
soil, in quantities indicated by Table 3. The pots were placed in two rows on a 75 cm high bench
and remained outdoors during the experimental period. Each treatment was replicated thret
times. The timothy was cut only once in each season and not before nitrogen deficiency had
become apparent; this happened only shortly after the heading out of the grass. Second growth
proved to be negligible in all the seasons in question.
The first two trial years will not be reported here, but in 1956 experiments with radioactive
phosphorus were initiated, with the aim of collecting information relative to the phosphorus up-
take by grass from soil phosphorus and fertilizer phosphorus. Radioactive monocalcum phos-
phate (CafH^POi)^) was added to a solution of known strength of this compound.
The effect of phosphorus for a silt loam and a peat soil.
In Table 2 arepresented data relating to the effect of increasing phosphorus fertilization. Three
rates of application were used, corresponding to 60, 90 and 120 kg P2O5 per hectare.
The yield was significantly increased with increased phosphorus rates for both soils (column
No. 1). The reasons for the low yields of the peat soil in 1958 are unknown.
The phosphorus content of the grass increased when the phosphorus rate changed from 82.8
mg P to 124.2 mg P per pot, but remained unchanged for the largest dose, 165.6 mg P (column
No. 2).
The total quantity of phosphorus taken up increased with increased phosphorus fertilization.
The soils in question differed little and insignificantly in this respect (column No. 3).
Column No. 4 lists the „apparent phosphorus balance" of the soil (see page 32). This ratio
was at maximum (25 per cent) for the lowest phosphorus dose, and decreased with increased
rate of phosphorus fertilization.
Column No. 5 tells what per cent of the phosphorus taken up by the grass came from fer-
tilizer applied at the beginning of the growing season. These figures were found with the aid