POTATO-MANURING IN THE SOUTH ISLAND.

New Zealand Journal of Agriculture, Volume 41, Issue 3, 20 September 1930, Page 164

POTATO-MANURING IN THE SOUTH ISLAND.

RECOMMENDATIONS TO GROWERS FROM EXPERIMENTS OF

SEASONS 1924-25 TO 1929-30.

Fields Division, Department of Agriculture.

During the past six seasons over sixty experiments have been conducted by the Fields Division on the manuring of potatoes. A report dealing more fully with these trials will be published in a subsequent issue of the Journal. • It is considered desirable, however, to present the salient features of these trials and the recommendations arising from the results for the guidance of farmers prior to the planting season of 1930-31.

Up to and including 1927-28 the work was confined to Canterbury, but in 1928-29 it was extended to Otago and Southland, and in 1929-30 to Marlborough. Two experiments were conducted in 1924-25, and over twenty in 1929-30.

Only those experiments which have formed the major part of the work are considered here. Two principal types of experiments will be dealt with—namely :—

A. Those in which different quantities of superphosphate were compared with one another and with no manure.

B. Those in which the effect of adding potash and nitrogen to superphosphate was investigated.

Type A Experiments

The treatments were : (1) No manure ; (2) super at 3 cwt. per acre ; (3) super at 5 cwt. per acre ; (4) super at 7 cwt. per acre.

SUPER 3 CWT. PER ACRE VERSUS NO MANURE.

It has been possible to compare the effect of using 3 cwt. of super per acre against no manure in thirty-six trials. In thirty-one of these super gave significant increases in yield of table potatoes ranging from 4 cwt. to 2| tons per acre. A summary of the approximate average increases per acre of the table and seed potatoes, calculated on thirty-six experiments, is as follows : Table, 20 cwt. ; seed, 6| cwt. : total, 26| cwt.

Note. —In all trials the yields of small potatoes, which are usually left on the ground or fed to pigs, were also measured, but are not included here.

SUPER 5 CWT. VERSUS SUPER 3 CWT. PER ACRE.

These treatments have been compared in nineteen experiments. In seven trials super 5 cwt. caused significant increases over super 3 cwt. Most of the increases occurred on land of natural high fertility and good water-retaining capacity, such as the Kaiapoi potato soils in Canterbury. The average increase per acre of super 5 cwt. over super 3 cwt. for nineteen experiments is as follows: Table potatoes, 4I cwt. ; seed, 2 cwt. : total, 6| cwt.

SUPER 7 CWT. VERSUS SUPER 5 CWT.

Only three out of nineteen experiments revealed a significant ■superiority of super 7 cwt. over super 5 cwt. in yield of table potatoes. 'The average over the nineteen trials shows a superiority of super -7 cwt. over super 5 cwt. to the extent of 4 cwt. of table potatoes and 1 cwt. of seed per acre.

Type B Experiments.

The treatments were : (1) Super 3 cwt. ; (2) super 3 cwt., plus •sulphate of ammonia 1 cwt. ; (3) super 3 cwt., plus sulphate of potash 1 cwt. ; (4) super 3 cwt., plus sulphate of,. ammonia 1 cwt., plus .sulphate of potash 1 cwt.

EFFECT OF ADDING NITROGEN IN THE FORM OF I CWT. OF SULPHATE OF AMMONIA TO SUPER.

Comparisons between super plus sulphate of ammonia and super have been made in thirty-three experiments. In eighteen of these significant increases in the yield of table potatoes due to sulphate of ammonia have ranged from 6 cwt. to 24 cwt. per acre. The average increases per acre in table and seed potatoes for the thirty-three •experiments are as follows : Table, cwt. ; seed, 5 cwt. : total, 14I cwt.

Climatic conditions rather than soil-fertility appear to effect the response to nitrogen. Dry conditions, especially after December, seem to inhibit the beneficial action of nitrogen.

EFFECT OF ADDING SULPHATE OF POTASH TO SUPER. Out of thirty experiments potash has increased the yield of table potatoes significantly in nine cases. The increases have ranged from •6 cwt. to 36 cwt. The average increases per acre in table and seed •potatoes for the thirty experiments are : Table, 5f cwt. ; seed, cwt. : total, 7 cwt.

Soil rather than climatic conditions appear to effect the response to potash. Potash responses have been most marked in Southland at Gore and McNab, but have occurred in Canterbury at Temuka, Willowbridge, Mitcham, Kirwee, and Leeston.

EFFECT OF USING A COMPLETE MIXTURE OF SUPER, PLUS SULPHATE OF POTASH, PLUS SULPHATE OF AMMONIA. In general, sulphate of ammonia has given results when added to super plus potash similar to those resulting from its addition to super •alone. Results from potash added to super plus sulphate of ammonia have been somewhat similar to those resulting from the use of potash with super alone. The scope of this article does not allow full discussion of a few anomalous results which have occurred.

Recommendations to Farmers. (1) The use of super at 3 cwt. per acre is strongly recommended. ■On the better-class potato soils heavier quantities are worth trying, "but on the lighter . soils, less retentive of moisture, there is no justification for using more than 3 cwt.

(2) The indications are that,' if used consistently, sulphate of ammonia at I cwt. per acre as an addition to super will pay. Sinceresponse to nitrogen appears to be governed by the season's weather conditions, and since it is not possible to forecast these conditions, it seems likely that only the consistent use of sulphate of ammonia can hope to recover in the good “ nitrogen seasons ” what little it' may lose in the unfavourable ones.

(3) In parts of Southland potash appears to be the most important limiting manurial factor .in potato-growing, and its use, especially in conjunction with superphosphate, should not be neglected. Sulphate of potash should be used. In Canterbury the trial of potash would appear to be justified in the districts indicated. The results indicate that potash is not such an important factor in, Canterbury as in England and Europe, where it is used almost universally for potatoes..

(4) A limited amount of experimental evidence indicates that application of manures in the row is better than broadcasting before sowing. Where suitable machinery is not available, hand application, in the row should be practised.

— A. W. Hudson,

Crop Experimentalist, Plant Research Station, Palmerston North.