POTATO-MANURING IN THE SOUTH ISLAND.

New Zealand Journal of Agriculture, Volume 43, Issue 3, 21 September 1931, Page 199

POTATO-MANURING IN THE SOUTH ISLAND.

SUMMARY OF EXPERIMENTS IN PAST SIX SEASONS.

A detailed report has been prepared on potato-manuring experiments in the South Island conducted by the Fields Division during the past six years, but cannot be published in full in the present issue of the Journal. In order, however, to make the more essential information available to growers in connection with the present season’s work, the salient features and recommendations as summarized in the report are here presented.

Summary.

(1) The results of fifty-six experiments in the South Island (mainly in Canterbury Province) conducted in the four seasons 1927-28 to 1930-31 inclusive are given.

(2) The effects on yield of various fertilizers used in sixtythree trials covering six seasons, 1925-26 to 1930-31 inclusive, are analysed.

(3) Nearly all trials were carried out on a co-operative basis on farms, using a system of six to twenty replications of plots in the various experiments.

(4) In most cases the crops were weighed in the various recognized grades —namely, table, seed, and small (or pig) potatoes. (5) The results of all experiments were submitted to statistical examination, “ Student’s ” method being used generally.

(6) The chief objects of the trials were :

(a) Comparison of no manure with superphosphate at 3 cwt., 5 cwt., and 7 cwt. per acre.

(6) Determination of the effect of using sulphate of ammonia and sulphate of potash, each at 1 cwt. per acre, as single additions to super and together with super, the latter being used at 3 cwt. per acre.

(c) Comparison of the ammonium phosphates —Ammophos and Diammonphos—with equivalent amounts of phosphate plus nitrogen in the form of a mixture of super and sulphate of ammonia.

(J) Determination in three trials of the effect of adding sulphur, at 3 cwt. per acre, to a mixture of super plus sulphate of ammonia plus sulphate of potash.

(7) Super at 3 cwt. per acre is compared with no manure in forty-four trials. It is considered that forty-one of these show significant increases due to the use of super. The general average increases (forty-four trials) are 0-96 tons (19 cwt.) and 0-25 tons (5 cwt.) of table and seed potatoes respectively. On the basis of value of potatoes and costs of fertilizers adopted this results in a net profit of about £2 9s. 6d. per acre, or 330 per cent, return on the outlay of about 15s. per acre for 3 cwt. of super.

(8) Increasing the quantity of super to 5 cwt. per acre in nineteen experiments gave satisfactory and highly paying returns only on the better-class potato soils of a rich alluvial nature. In seven experiments on such soils the net return per acre from 5 cwt. of

super was £4 10s. On light to medium soils the use of more than 3 cwt. per acre is shown to be not justified.

(9) Increasing the quantity of super to 7 cwt. per acre in eighteen experiments gave inconsistent results. A few increases over super at 5 cwt. are recorded, and in two experiments yields were depressed by the use of 7 cwt. below that from 5 cwt.. In the main there is no justification for using more than 5 cwt. of super per acre, even on the better-class potato land.

. (10) The use of sulphate- of ammonia at 1 cwt. per acre as an addition to super in thirty-six trials shows a general average- increase over super alone of about 0-48 tons (g| cwt.) and 0-27 tons (5| cwt.) of table and seed potatoes respectively. 7 This represents a net profit of about 255. per acre, or approximately 200 per cent, on the outlay for sulphate of ammonia.. When used with super plus potash the effect of sulphate of ammonia is very , similar. . The effect of sulphate of ammonia on yield appears to be influenced by climatic conditions. Dry midsummer weather generally results in poorer returns than when the . rainfall is fairly well distributed.

(11) The effect of sulphate of potash to a paying extent appears to be limited to certain districts which are represented by experiments conducted, at Kirwee (North -Canterbury) Mitcham (MidCanterbury), Temuka and Willowbridge (South Canterbury), Taieri (South Otago), McNab and Gore (Southland). In the case of Willowbridge the economic value of potash is doubtful.

(12) Super plus sulphate of ammonia has proved superior to the ammonium phosphates —Ammophos or Diammonphos —in four experiments out of eight; but neither of these has proved superior to the mixture of super plus sulphate of ammonia. It is concluded, therefore, that in the main this mixture is more effective than the ammonium phosphates.

(13) Sulphur proved effective in. increasing the yield in one experiment, but its use at the current price of sulphur was not profitable.

Recommendations to Growers.

(1) Superphosphate. — On the lighter to medium-class potato soil use up to 3 cwt. of super per acre. On the rich alluvial potato soils use up to 5 cwt. of super per acre.

(2) Sulphate of Ammonia. — Use 1 cwt. of sulphate of ammonia per acre, in addition to super recommended above, on all soils.

(3) Sulphate of Potash. — Use 1 cwt. of sulphate of potash, in addition to the super and sulphate of ammonia, in those districts named in section 10 of the foregoing summary with the possible exception of the Willowbridge district, where results are conflicting. Potash is at least worth trying in that district, and there may be others not covered by the experiments in which potash is worth using.

(4) Application of Manures..- farmers who have no potatoplanting machine which sows manure, nor a manure-box attachment for ' the plough, are strongly advised to apply manures by hand or with a hill-country hand top-dresser 'of the Hillman type. Applied in this way the ' fertilizer should "be spread in a strip about 3 in. to 4 in. wide along the bottom of the' furrow in which the

potatoes are planted afterwards. Confining the manure to a narrow strip is likely to render it more efficient than broadcasting it over the whole width of the furrow. Contact with fertilizers used at the rates recommended is not likely to damage the sprouting of the potatoes -so long as the manure is spread before the potatoes are planted. If cut seed is used it would be advisable not to allow the potatoes to come too freely in contact with the manure, however. - " - ~ ”* m '

A. W. Hudson,

, Crop Experimentalist, and J. W. Woodcock,

Assistant Crop Experimentalist.