Recent Research Work: Potassic Fertilisers for Topdressing

New Zealand Journal of Agriculture, Volume 84, Issue 3, 15 March 1952, Page 216

Recent Research Work: Potassic Fertilisers for Topdressing

AN INTENSIVE STUDY of the AN INTENSIVE STUDY of the 'A potash requirements of soils i

Taranaki, Rotorua, and Matamata N| districts has been carried out recently. Experiments, have shown that pastures on many North Island soils derived from volcanic ash, many of the sandy soils, and most peats and peaty soils are now showing definite responses to potassic fertilisers. There is evidence that potash deficiency often becomes more marked and widespread after, the soils have been farmed for many years. Any farming practice causing soil depletion, such as the cutting of a paddock for hay for a number of years, soon results in .a deficiency . of . potash on such a field. Work is in progress on the soil types known to be potash deficient to determine the .best rates and times to apply potassic fertilisers. On most soils an initial dressing of I cwt. per acre of muriate of potash followed by annual, applications of |cwt. will give good results, though most peats and peaty soils require considerably higher applications than this.

TARANAKI TRIALS

THE VALUE of potash for pasture topdressing was recognised by some Taranaki farmers on certain

J._Ld-IXX XdX X M WXX VMXXX soils 30 years ago and their experience was confirmed in the early 1930’s by a plot survey carried out by J. M. Smith and A. G. Elliott. In spring 1947 a series of half chain square plots was laid down on the main soil types of north Taranaki to define more exactly the potash deficient areas. The survey has shown that potassic fertilisers have had a marked effect on all soils derived from Egmont or Stratford ash, but little or no response was obtained from trials on the Whangamomona silt loam. On some trials potash responses were not evident until after phosphates were applied.

CLOVER RESPONSES

Potassic fertilisers brought about a marked change in pasture composition. Clover in-

creased from 10 to 30 per cent.; weeds were reduced from 25 to 30 per cent. of the sward to 10 to 15 per cent. within a few months. The accompanying table shows the effect of one dressing of lcwt. of muriate of potash on the clover content of the swards on the trial plots.

EFFECT OF POTASSIC FERTILISERS ON CLOVER CONTENT OF TARANAKI PASTURES Clover content • No potash Potash District ; Soil type Per cent. Per cent. Fataraimaka .. *Egmont silt loam .. ..10 25 Okato .. .. New Plymouth silt loam .. 20 30 Pukearuhe .. *New Plymouth silt loam ..15 30 Lepperton .. New Plymouth sandy loam .. 20 , 30 Inglewood ..- Stratford sandy loam .. .. 20 30 Inglewood .. Inglewood coarse sandy loam .. 10 30 Carrington Road Patua sandy loam .. ..20 30 * Black phase

Not only were there marked clover increases on the potash-treated plots, but the swards kept greener and more vigorous and palatable at all seasons than untreated areas. Soil samples from 29 trials were examined by quick-test methods for available potash, and comparison of. results with field responses showed a satisfactory measure of agreement. Certain anomalies were explicable through lack of phosphate also limiting growth. In two or three cases only were potash responses obtained when quick-test methods showed that the soil was apparently well supplied. —A. C. BURGESS ■ ♦ * ♦ ♦

AUCKLAND TRIALS

THOUGH many soils of the Auckland Province are initially low in potash, this is not revealed in farming them until other more serious deficiencies are met. Thus the more heavily

leached soils in North Auckland show responses to potash only where the lime and phosphate content has been built up. On many areas in North Auckland the lime and phosphate status has not reached a sufficiently high level for farmers to obtain results from potash. On the brown loams and other less lime-deficient soils results from potash are being obtained on farms and there is an immediate need on such soils for

potash applications. Large areas of South Auckland have been so intensively farmed and so well topdressed with phosphates (the main deficiency) that potash applications produce material improvement.

Where marked potash deficiencies occur some outstanding results have been obtained in experiments in which potash fertilisers have been used. For example, on a peat soil in the Te Aroha district dressings of phosphate, of lime, and of various minor elements gave little or no response, but marked increases in pasture production were obtained from muriate of potash. On the plots receiving the heaviest dressing (12|cwt. of muriate of potash over 3 years) yields were nearly three times as great as on no-potash plots; on plots receiving the lightest dressing (2|cwt. of muriate of potash over 3 years) yields were about 60 per cent, above no-potash plots. At these rates of increase even the heaviest dressings of potash appear worth while. Most peat soils are extremely deficient in potash, and yield increases comparable with those mentioned are not usually found on the majority of mineral soils.

—J. E. BELL