MANURING OF EARLY POTATOES.

New Zealand Journal of Agriculture, Volume XXXIV, Issue 3, 21 March 1927, Page 165

MANURING OF EARLY POTATOES.

EXPERIMENTS IN AUCKLAND PROVINCE, 1926.

T. H. Patterson,

, H.D.A., Instructor in Agriculture, and J. W. Woodcock, N.D.A.,

Assistant Instructor in Agriculture, Auckland. The growing of early potatoes is a feature of farming in certain districts in the Auckland Province. Free-working loams of good quality, combined with freedom from damaging frosts, are the natural factors favouring success. Though the yield of. the early crop is comparatively light (from 5 to 6 tons per acre being considered quite satisfactory), the manuring is heavy, and the growers claim that very liberal manuring pays because of the high prices secured for the earliest “ new ” potatoes. Two crops and a crop of “ seed ” are taken in one season from the same ground. The residue of the manure from the early crop assists the main crop which follows. Official statistics for 1925-26 show that an area of 2,900 acres was sown in potatoes in the Auckland and North Auckland Land Districts. As the information is collected in September of each year this area -—-which only includes areas of 1 acre or more—-takes in all the crops intended for the early market as well as those to be sown for the main crop. The usual rotation is potatoes after grass two or three years old. Some of the more progressive growers include a crop like mustard, which is ploughed in ; it adds organic matter and assists drainage consideration of importance in the wet winters. Other cash crops, such as onions, mangolds, and carrots, are also grown. The very early crops are generally taken, as stated, from favoured districts where the soil is a suitable free-working loam, and where frosts which do any damage rarely occur. The higher lands (which are high-priced) of Franklin County fall into this category. “ The Hill ” at Pukekohe is best , known, and is one of the favoured places where potatoes are grown for the very early market, the crop coming in sometimes during the first week of September. The earliest consignments are sent to Wellington, and even to the South Island, where the wholesale price realized is 4d. to sd. per pound. When the market weakens in the South, which usually occurs about early ■October, the potatoes are put on the Auckland market and are sold at 2d. to 3d. per pound. When the price goes down to i|d. a pound or a little less the growers usually reduce supplies until the price advances. Last season 8,000 tons of potatoes were sent from Pukekohe, representing £72,000 in value. This season it is estimated that 9,000 tons will be trucked by 31st March.* Other districts which supply ■early potatoes are Kerikeri (Bay of Islands), Whangarei, Helensville, Avondale, the Waitakeres, Onehunga, Mangere, Papatoetoe, Papakura, Waiuku, and Taupiri. With a few exceptions, the potatoes are grown ■on volcanic soil. A factor which helps the grower with his early crop in these districts is that he has not the competition of growers in the South.

The demand for early potatoes is increasing with the increase in population, and new districts are coming into the early-potato industry. These districts encounter less , disease than the older places, and the new ground gives a better sample, as the shape comes back because of the greater vigour in the tuber. Manuring of the early-potato crops in the older districts has undergone a great change from thirty years ago, when, and until recent years, a ton of bonedust per acre was the usual dressing. The. increase in price of bonedust, together with the results of experiments in manuring, have been the chief factors in altering the manural prescription. Thirty years ago, when the early-potato industry was in its infancy in the province, bonedust was sold in Auckland at £5 12s. 6d. per ton ; in 1914 the price was £8 ; to-day it is about £l2. In 1922 it was higher still—in fact, it was quoted in Auckland at £23 a ton after the war, when all manures were scarce. High prices directed attention to other fertilizers, such as the lower-priced phosphates, including superphosphate and ground raw rock. From a record recently made' of twenty-two growers in the Pukekohe district it was' found that fifteen used a mixture of super and bonedust, two used bonedust alone, and the remainder used proprietary manures. The average dressing per acre of growers using bonedust and super was 5 cwt. of super and 11 cwt. of bonedust. An average dressing of i| cwt. of. sulphate of potash was used in every case. It will be seen that for years bonedust. was the only manure added, and although its increased price lead to the inclusion of super, large quantities of bonedust still formed the chief phosphatic dressing.Scheme of the Experiments. The aim of the experiments here recorded, established at Pukekohe, Taupiri, and Kerikeri, was to. see how far a less costly phosphate could economically replace all or part of the bonedust. , The mixtures used were as follows :• —■

: Per Acre. . (i) Bonedust ... . . . ‘ .. 15 cwt. Sulphate .of potash ..• .. 2 cwt. ' . . . . Per Acre. Per Acre.. (2) Bonedust ; .. : .. 7I cwt. (3) Superphosphate (44-46) 7I cwt. <Superphosphate (44-46). . 7J cwt: •. Ephos phosphate . . 7I cwt. Sulphate of ammonia . . cwt. Sulphate of ammonia . . 3J cwt. - Sulphate of potash . . 2 cwt. Sulphate of potash ..2 cwt.

• It will be seen that the amounts of phosphatic fertilizers were kept constant, but were different in type. In No. 2 mixture half the bonedust has been replaced by superphosphate, and in No. 3 all the bonedust has been 1 eplaced by a mixture of super and Ephos. The bonedust used was a locally manufactured green-bone product which is popular with the growers at Pukekohe ; its analysis was 48-32 percent. tricalcic phosphate, and 4-2 per cent, nitrogen. An equivalent amount of nitrogen was substituted where bonedust had been replaced by the addition of sulphate of ammonia. The amounts of nitrogen and potash were therefore kept constant in all the mixtures. Each plot consisted of three rows of potatoes .28 in. apart, and was adjacent to a plot of different treatment. This series was continued several times across the field. When dug all the rows were weighed,

but only the weight of the middle row of each plot was /taken for comparison. At all three locations cut sets of the “ Gamekeeper ” variety were used for seed, being planted by hand and ploughed in, the manure having previously been weighed out and applied along the face of the furrow. Trial on Farm of E. J. Campbell, Pukekohe. In this experiment sowing was done on 21st and 22nd June, and weighings made on Bth, 9th, and 10th November, 1926. The field selected for the. experiment, although not having sufficient altitude to produce the earliest of crops, consists of a good friable volcanic loam typical of Pukekohe Hill. It had been in grass for many years, and there was a splendid sole previous to ploughing, providing a good supply of organic matter for the crop. The importance of this humus supply probably had a direct bearing on the result, as will be seen later. The rows were 7 chains long, and the series of plots were repeated six times across the held, so that each treatment was compared with another forty-two times when weighings were made at every chain. ' Observations during Growth.— From the time .the plants appeared above ground until digging, the super and Ephos plots, and to a lesser extent the super and bonedust plots, appeared to be ahead of the bonedust. This fact was noticed by several observers during the growth period. The haulms of the super plots ripened off quicker, and it may be safely maintained that the inclusion of super in the mixtures has been conducive to an earlier ripening. This is a most important consideration in the growing of early potatoes, since a gain of two or three days at digging-time may mean the difference of id. or more per pound in some seasons.

Basis of Comparisons.— All the rows were dug separately by hand and the tubers graded into marketable and small. At that time of the year potatoes were quoted at £l2 per ton, which is a figure well below that ruling in recent years at the same period. In Table r and subsequent tables no value has been placed on the small unsaleable potatoes, since these are usually kept by the diggers. The comparisons in all the tables have been worked out by “ Student's ” statistical method, under which a difference is regarded as significant when the chances are 30 to 1 or more in its favour.

COMMENTS ON TABLE I. (1) Super and Ephos versus bonedust : The substitution of mineral phosphates has resulted in an increase of over 151 cwt. of saleable potatoes, besides lessening the cost of manuring. Allowing £lO as the net value per ton after deducting the cost of digging and carting (£2 per ton), and adding the difference in the cost of manures, the profit derived has amounted to £9 7s. 3d. per acre. (2) Super and bonedust versus bonedust : Here again the. increase is appreciable, and the gain by substituting super for half the bonedust amounts to £7 is. yd. per acre. (3) Super and Ephos versus super and bonedust : When these two are compared with one another there is a difference of 22 cwt. in favour of super and Ephos, representing a gain of £i 15s. Bd. per acre. This, however, is not significant when taken statistically. The cost of manures taken in the above . calculations was based on the prices ruling at • the time of planting. The recent reductions in the price of superphosphate would show a still greater gain in the superphosphate mixtures.

Bonedust still has many adherents by reason of its “ lasting ” qualities or residual effects. One has often heard it said that “it is so good for the grassland afterwards.” But a pound in the hand is probably worth more than two in the ground in these days when the slogan of “ quick returns ” is being increasingly applied to agriculture. What residual value would compensate for a cash increase of £g per acre as in the case of super and Ephos, or £7 as in the case of super and bonedust ? From our experiments in pasture top-dressing at Pukekohe it would pay better to spend money on 3 cwt. per acre of a suitable phosphate than depend on the residue of bonedust. An attempt is being made at Pukekohe and Taupiri to test the residual effect of the manures used in these experiments, and the results of this investigation will be published at a later date. Trial on Farm of A. Wright, Kerikeri. The Kerikeri district, Bay of Islands, has only recently been connected with the early-potato industry, but the mildness of its winter and its freedom from frosts make it ideally suited for that purpose as far as climate is concerned. The soil here is volcanic, of a pebbly ironstone nature, lighter than the Pukekohe soil, but lacking in humus. The only area available sloped in two directions, and thus running the rows across a slope was unavoidable. The field was previously in grass, but the turf was very poor, consisting mainly of Chewings fescue and danthonia. Consequently there was little addition of humus to the soil after ploughing. Sowing was done on 12th and 13th May, and the crop was dug on 4th and sth October, 1926. The rows were 5 chains long, and the series was replicated four times across the field so that twenty comparisons could be made. Observations during Growth— was no appreciable difference between the individual rows at any time, except that those running along the foot of the slope looked better, and in fact weighed out better, than those at the top, a result obviously due to better fertility. Comparisons op Yield.- the rows were dug by hand and sorted into grade 1, grade 2, and small sizes, each grade being weighed separately. The price obtained for the first grade was 3d. per pound, and for second grade rd. per pound, in the Auckland market. Particulars of results are set out in Table 2 (next page). COMMENTS ON TABLE 2. Super and bonedust versus bonedust : The combination of super and bonedust has at this centre shown its superiority over the other mixtures, and has given an increase of more than io cwt. over bonedust alone. This increase is valued at £l2 10s., giving a profit of £l3 ss. pd. when compared, after allowing £2 per ton for digging and £2 ios. per ton for carting and freight to Auckland. The manures have been valued at the ruling price at planting, plus freight from Auckland. . x Super and bonedust versus super and Ephos : The difference here has been remarkable, and the position as at, Pukekohe entirely reversed. The super and bonedust gave an increase of over 19 cwt. of saleable potatoes when compared with super and Ephos. The profit derived

by using the former mixture amounts to £22 13s. 96.., a very large figure, magnified, no doubt, by the high price obtained for the produce. • - Super and Ephos versus bonedust : The bonedust gave an increase in grade potatoes of 3 cwt. 81 lb., but this increase was counterbalanced by an increase of over 3 cwt. of second grade in favour of the super and Ephos. These results, however, are not significant when treated statistically, so that no reliance can be placed on them.

NECESSITY OF ORGANIC MATTER. The results at Kerikeri for the past season go to show that superphosphate can. replace bonedust to a certain extent, but that under similar conditions bonedust cannot wholly be replaced. The explanation of this probably lies in the poor supply of humus in the Kerikeri soil. It has been repeatedly proved in the past that for yield the potato crop must have a good supply of organic matter to be a success. In Great Britain and on the Continent of Europe this demand is satisfied by a large application of farmyard manure. Up to 15 tons of farmyard manure per acre are applied, together with artificials. In fact, the conclusions arrived at by Hall after twentysix years of manuring potatoes at Rothamsted are that the best

basis for the growth of potatoes is a supply of well-rotted farmyard manure. He goes on to state that in the absence of farmyard manure it should be replaced by some manure containing organic nitrogen. Now, while it is almost impossible in this country to make such an application of farmyard manure, the ploughing-in of a green crop or the turning-under of a good grass turf goes a long way towards supplying the potato crop with the necessary organic material. At Pukekohe this object was attained, and the substitution of mineral fertilizers was highly successful. The supply of organic matter at Kerikeri was limited, consequently that same success with entirely mineral fertilizers has not been forthcoming. Trial on Farm of S. V. Bilkey, Taupiri. The soil at Taupiri is slightly heavier than the Pukekohe soil, and it varies to a certain extent. The area selected was formerly in grass, which was not of good quality, being largely composed of the twitches, but the soil itself was not lacking in organic matter. - Sowing was done on 30th June, and the crop was dug on 22nd and 23rd November, 1926.. The rows were 4 chains long, but the series was replicated five times so that twenty comparisons could be made. Observations during Growth. As at Pukekohe, the super and Ephos plots went ahead soon after the plants were above ground, but this superiority was not maintained later in the season. The soil at one side of the area was heavier than the rest, and during the winter became very sticky. It was noticed when digging the crop that here the bonedust gave much better yields.

COMMENTS ON TABLE 3. The odds here are not great enough to be regarded as significant, on account of the soil-variation, but the results go to show that both super and bonedust and super and Ephos tend to give better results than bonedust alone. General Conclusions. While it is rather risky to generalize from too few data, some important points stand out from the results secured so far. It must be remembered that as the tilth of the soil plays so important a part with potatoes the response to manures will vary very greatly with the thoroughness or otherwise of cultivation. . (1) Bonedust can be replaced partly and in some cases wholly by mineral phosphates. (2) The inclusion of superphosphate in the mixture has in practically every case resulted in an increased yield, besides lessening the cost of the manure. Early ripening has also been encouraged. (3) Where there is a good supply of humus in the soil it is probable that the use of bonedust can be dispensed with altogether, and a mixture of mineral phosphates such as super and Ephos substituted. (4) The residual effects of bonedust are far outweighed by the increased return where super is used. In some cases this profit has amounted to more than the cost of the manure used. What effect the residues will have on the succeeding crop of potatoes will be probably seen later. (5) These results were obtained in a season when the rainfall was about the average. There is every reason to suppose that in a drier season the odds would still further favour the water-soluble superphosphate. (6) The results of these experiments suggest further investigations. Questions which should be answered by field trial are : (a) How far can super profitably replace slower-acting phosphates like bonedust and rock phosphates ? (&) Can the total amount of manure used per acre be economically reduced ? We offer the growers, Messrs. B. V. Bilkey, E. J. Campbell, and A. Wright, our thanks for their co-operation in securing the results recorded. We thank Mr. A. E. Lovell, Stationmaster, Pukekohe, for information freely given. We also acknowledge the help rendered by our colleagues in the Fields Division. .

Tenures of Land-holdings.— The official agricultural statistics give the following particulars concerning the tenures of occupied land in New Zealand for 1926 : Freehold (including land held on deferred payment), 20,451,217 acres ; Crown leases and licenses, 19,007,447 acres ; leases from private individuals or public bodies, 2,549,538 acres; leases from Maoris, 1,598,482 acres; unspecified, 145 acres. Freehold land formed 46-90 per cent, of the total area occupied in 1926, as compared with 47-06 per cent, in the preceding year.

* Figures supplied by Mr. A. E. Lovell, Railway Stationmaster, Pukekohe.

* Yield of small potatoes not treated statistically.

S. = Significant difference ; N.S. = Non-significant difference.

S. = Significant difference ; NS. = Non-significant difference.

Type of Phosphate. ' Yield per Acre. Cost of Manures per Acre. Value of Increase per Acre. Profit per Acre. Difference significant (S.) or nonsignificant (N.S.). Table. Small.* Tons cwt. Cwt. £ S- d - s - d - Z s - d - 15 cwt. super and boneTons cwt. 6 6-8 Cwt. 8-75 £ 9 12 5 s. 12 1. 5 £ s. d. s. d.. dust 15 cwt. bonedust 5 14’4 I 4 -4 7'50 7\5o 10 10 0 10 10 0 In favour of super and I2‘4 1-25 640 7 I 7 s. bonedust 12-4 1-25 6 4 0 7 1 7 s. 15 cwt. super and Ephos 6 g-o 7’25 818 9 15 cwt. bonedust 6 5 E3-4 9-0 13-4 7-50 7’25 7’50 10 10 0 8 10 18 10 9 0 In favour of super and 15-6 7160 9 7 3 s. Ephos 15-6 7 16 0 9 7 3 s. 15 cwt. super and Ephos 6 9-0 9-o 818 9 1 5 cwt. super and bone6 6-8 9-2 9 12 5 dust 6 6 9-o 6-8 9-0 9-2 8 9 18 12 9 5 In favour of super and 2-2 12 0 1 15 8 N.S. Ephos 2-2 1 2 0 1 15 8 N.S.

Table I. —Summary of Results at Pukekohe.

Type of Phosphate. Yield per Acre of Saleable Potatoes. per Acre of Saleable Potatoes. Cost of Cost of Manures per Acre. Value of Increase per Acre. Profit per Acre. First Grade. Second Grade. Total. Small. per Acre. Tons cwt. lb. Tons cwt. lb. Tons cwt. lb.. Cwt. lb. £ s. d. £ s. d. £ s. d. 15 cwt. super and 4 3 43 I I 28 5 4 7 1 6 84 IO 15 6 bonedust 15 cwt. bonedust Tons cwt. lb. 4 3 43 3 13 3i Tons cwt. lb. I I 28 I O 84 Tons cwt. lb.. 5 4 7i 4 14 3 Cwt. lb. 6 84 5 7° £ s. d. 10 15 6 11 11 3 £ s. d. £ s. d. In favour of super O IO 12 0 0 56 0 10 78 1 14 12 IO O 13 5 9 and bonedust . s. N.S. S. 15 cwt. bonedust 3 8 25 0 17 77 4 5 102 5 6 11 11 3 15 cwt. super and 3 4 56 1 1 0 4 5 56 6 0 10 3 9 Ephes 0 10 12 . s' 3 8 25 3 4 56 O O 56 N.S. 0 17 77 11 0 0 10 78 S. 4 5 i°2 4 5 56 1 14 5 6 6 0 11 11 3 10 3 9 12 IO O 13 5 9 In favour of bone0 3 81 0 0 46 3 15 0 276 dust In favour of super 0 3 35 0 106 and Ephos N.S. N.S. N.S. 15 cwt. super and 4 3 43 1128 5 4 7i 6 84 10 15 6 bonedust 15 cwt; super and 3 4 56 1 1 0 4 5 56 6 0 10 3 9 Ephos 0 3 81 N.S. 4 3 43 3 4 56 0 3 35 N.S. I 1 28 II 0 0 0 46 N.S. 5 4 7i 4 5 56 0 106 6 84 6 0 10 15 6 10 3 9 3 15 0 276 In favour of super 0 18 99 0028 0 19 15 0 84 23 5 6 22' 13 9 and bonedust 0 18 99 S. 0028 N.S. 0 19 15 S. . 0 84 23 5 6 22' 13 9 -

Table 2. —Summary of Results at Kerikeri.

■ ; Type of Phosphate. Yield per Acre. Cost of. ■ Manures per Acre. Value of . Increase per Acre. Profit . per Acre. Table. Seed. Total. Tons cwt. lb. Tons cwt. lb. Tons cwt. lb. £ s. d. £ s. d. £ s. d. 15 cwt. super and bonedust 4 8 49 Ill O 5 19 49 9 12 5 15 cwt. bonedust 4 3 43 160 5 9 43 IO IO 0 In favour of super and 056 0 5 0 010 6 608 6 18 3 bonedust N.S. N.S. N.S. 15 cwt. super and Ephos 416 2 1 9 68 6 5 7° 8 18 9 15 cwt. bonedust 4 !2 56 1 6 30 5 18 86 10 10 0 In favour of super and 0 3 58 0 3 38 0 6 96 423 5 13 6 Ephos N.S. N.S. N.S. 15 cwt. super and bone4 8 49 1 10 40 5 18 89 9 12 5 dust 15 cwt. super and Ephos 4162 1 9 68 6 5 7° 8 18 9 In favour of super and 0 7 65 0 6 93 4 in 4 15 7 Ephos In favour of super and 0 0 84 bonedust Tons cwt. lb. 4 8 49 4 3 43 Tons cwt. lb. I II O 160 Tons. cwt. lb. 5 19 49 5 9 43 £ s. d. 9 12 5 IO IO 0 8 18 9 10 10 0 9 12 5 818 9 £ s. d. 608 4 2 3 '•'4-/ ‘ III £ s'. d. 6 18 3 5 13 6 4 15, -7 O5 6 N.S. 4 16 2 4 12 56 0 5 0 ' N.S. 1 9 68 1 6 30 010 6 N.S. ’ 6 5 70 5 18 86 0 3 5 8 N.S. 4 8 49 4162 0 3 3 8 N.S. ' 1 10 40 1 9 68 0 6 96 ' N.S. 5 18 8 9 6 5 70 0 7 65 N.S. 0 0 84 N.S.. 0 6 93 N.S. ■ N.S. N.S.

Table 3. —Summary of Results at Taupiri.