A M E R I C A N P O T A T O J O U R N A L

|~ OFFICERS AND EXECUTIVE COMMITTEE | | J F. M. Harr ing ton , Pres ident . . . . . . . . . . . . . . . . . . . . . . . . . . College o f Agr icu l ture , Bozeman~ M o n t a n a ] |9 John Tucker, u 1 7 6 . . . . . . . . . . . . . . . . . . . Central E z p e r i m e n t a l F a r m , Ottawa~ Canada | | i H. C. Moore, Secre tary -Treasurer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E a s t Lamming, Mlehii~m J |~ E D Askegaard ........... Moorhead, Minnesota | ||il Miles" Hor~t ....... --_-__~_\-_: :-:::':- :-__:-_:=.:::::=::_:-_-_-_'____--_~_'"_-:._--_~- "_-..__Harrls~rg, Pennsylvania ] _ _ _ _ _ _ ,

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Potatoes and Soil Acidity

By P. H. W E S S E L S , L. I. Vege tab le R e s e a r c h F a r m

Changing soil reaction in order to promote crop growth is an old and well established agricultural practice. Careful adjust- ment of the soil reaction is not always necessary as many crops will thr ive on soils t h a t vary widely in the i r reactions. So long as a certain degree of acidity or alkalinity is not exceeded, the growth of the crop may be satisfactory. But crops vary in their requirements and when crops with widely different requirements are grown in rotat ions the adjus t ing of the reaction of the soil may become an important problem. Such is the case where po- tatoes are grown extensively and where certain other crops are also of importance as is the case in much of the potato-growing section of Long Island.

In order to obtain information regarding the response of vari- ous vegetable crops to variations in soil acidity, a series of sixty- five plots was laid out on the very level fields of the Long Island Vegetable Research Fa rm in June, 1924. The soil is classed as Sassafras sandy loam. Each plot is th i r ty-e ight feet long and sixteen and one-half feet wide with aisles four feet wide separat- ing the plots, which are arranged in five tiers of thi r teen plots each. Differences in soil reaction on these plots were obtained by applying powdered sulphur at the rates of 25, 75, 150, 250, 450 and 800 pounds per acre and hydra ted lime at the rates of 300, 750, 1500 and 3000 pounds per acre. One plot in each t ier was lef t wi thout t r ea tment to change the reaction and two plots in each t ier received applications of acid phosphate at ra tes to supply 150 and 300 pounds of P~05 per acre.

Cauliflower was grown on these plots in 1924. In 1925 a green manure crop of oats and field peas was sown. This was plowed

92 A M E R I C A N P O T A T O J O U R N A L

under in June and cauliflower again planted upon these plots. As the reactions had not been changed as much as was desired on the limed plots, another application of hydra ted lime was made, using the same amounts as had been applied previously.

In 1926 these plots were planted with Irish Cobbler potatoes. Fert i l izer was applied at the ra te of 1800 pounds of a 5-8-5 mix- ture per ~cre. The planting was done by hand and care was tak- en to have the number of hills the same on all plots. The rows were spaced th i r ty- three inches apar t and the hills were fifteen inches apar t in the row. No differences were noted in the t ime of coming up or the stand of plants secured, but as the season progressed it was easily seen tha t growth was depressed on all plots t ha t had received sulphur at the ra te of 250 or more pounds per acre; where smaller amounts were used the differences were not marked. The potatoes were dug Augus t 24 a f t e r the tops were dead. A careful examination for scab was made bu t only the meres t t race was found. The yields are given in table I.

TABLE I

Rel~tio~ of Soil Reaetion to Yield of Irish Cobbler Potatoes in 1926 (average of 5 replications)

P l o t T r e a t m e n t A v e r a g e T o t a l Y i e l d ( lbs . p e r a c r e ) pH* ( b u s h e l s p e r a c r e )

S u l p h u r - - 8 0 0 ........................................... S u l p h u r - - 4 5 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S u l p h u r 250 .............................................. S u l p h u r - - 1 5 0 ............................................. S u l p h u r - - 75 ............................................ S u l p h u r - - 25 ............................................. P205--300 .............................................. P ,O5--150 .................................................... B l a n k ................................................... H y d r a t e d L i m e - - 600 ........................... H y d r a t e d Lime---1500 . . . . . . . . . . . . . . . . . . . . . H y d r a t e d L i m e - - 3 0 0 0 .............................. H y d r a t e d L i m e - - 6 0 0 0 ..............................

4.7 4.9 5.0 5.1 5.2 5.3 5.3 5.3 5.3 5.3 5.6 6.3 6.6

160 180 204 226 231 243 259 251 236 242 260 242 239

* A v e r a g e a c i d i t y fo r t he f ive p l o t s in e a c h t r e a t m e n t . T h e s m a l l e r t h e num-

ber , t h e m o r e ac id t h e r e a c t i o n .

The figures in this table indicate tha t increasing the natural acidity of this soil tends to decrease the yields of potatoes, while decreasing the acidity has no very marked effect.

As we had not obtained the range of reactions desired, another application of sulphur was made, giving each plot one-half the amount applied previously. A cover crop consisting of rye, red- top, t imothy, perennial rye grass, alsike clover, medium red clover and hai ry vetch was then sown. The object in using such a mixture was to give each plot an opportuni ty to produce as

A M E R I C A N P O T A T O J O U R N A L 93

much organic matter as the reaction of the soil would permit. There was a good grov:th of cover crop. On the most acid plots it consisted almost entirely of rye and on the other plots of rye and grasses. Only on the plots that had received hydrated lime at the rates of 3000 and 6000 pounds per acre was there much clover. The hairy vetch did not survive the winter.

This cover crop was plowed under early in April in 1927 and the area planted with the Green Mountain variety of potato. The fertilizing and planting were the same as in 1926. A very uni- form stand was obtained and the appearance of the field was much the same as that noted in 1926---a considerable depression in growth on the more acid plots. There was a well graded im- provement in growth as the acidity decreased up to the plots which had received the smallest application of sulphur; beyond that there was not much difference in the size of the vines. The plants on the phosphated plots and on the limed plots remained green for several weeks after those on the more heavily sul- phured plots were dead. Although spraying with bordeaux mix- ture was continued as long as the plants remained green, blight was not controlled and the yields were cut by the rot that devel- oped on these plots where growth had continued longest.

The total yields, the amounts of potatoes carrying enough scab to unfit them for market, and the reactions of the plots as determined colorimetrically on the air dried soil are given in table II.

TABLE II

Relation of Soil Reaction to Yield and Quality of Green Mountain Potatoes in 1927 (average ~ff 5 replications)

Plot Treatment (lbs. per acre)

Sulphur--1200 Sulphur-- 675 Su lphur - - 375 Sulphur-- 225 Su lphur - - 1121/,_, Sulphur--- 371/.~, D:O~--300 l)~O~--150 Blank Hydrated l ime-- 600 Hydrated lime---1500 Hydrated lime---3000 Hydrated lime--6000_

Average pH

4.6 4.8 4.9 5.1 5.4 5.4 5.4 5.3 5.3 5.5 5.7 6.5 6.7

Total Yield ( bushels

per acre)

Scabby (unsalable)

(bushels per acre)

94 181 248 277 286 323 321 324 296 320 290 259 229

0.1 0.2 0.6 0.1 3.9 69 2.9 0.0 0.3 2.7

13.0 107.0 162.0

Scabby (unsalable) (per cent)

0.11 0.11 024 0.04 1.40 2.10 0.90 0.00 0.10 0.84 4.48

41.31 70. 74

Not enough data have been obtained to warrant any very de- cided statements, but it is evident that on this Sassafras sandy loam any increase in acidity beyond pH 5.2 is likely to result in

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decreased yields of potatoes. The results with both the early potatoes (Irish Cobblers) in 1926 and with late potatoes (Green Mountains) in 1927 agree on this. The evidence in favor of re- ducing the natural acidity of this soil for potatoes is not very s t rong but here we have only one season's results as there was so much rot present in the potatoes on the limed plots in 1927 tha t the .figures do not show the amount of crop actually pro- duced. The question of whe the r the yield of potatoes can be much increased by liming is a ve ry minor one, however, as com- pared with the effect tha t reducing the acidity of the soil may have upon the quality of the crop produced. The evidence here presented shows tha t with the Irish Cobbler var ie ty of potatoes, on land tha t had not grown a crop of potatoes for two years, it may be possible to produce one crop of scab-free potatoes where the acidity has been reduced to pH 6.6 through an application of hydra ted lime at the rate of 6000 pounds per acre. I t would be most unwise to advocate such a procedure on the basis of a sin- gle season's work. With the Green Mountain variety, scab was found to some extent on almost every plot, al though the amounts were very small where the reaction was more acid than pH 5.3. It is quite possible tha t the figures for scabby potatoes are too small on the limed plots as it was the opinion of those present at the t ime of harves t tha t most of the potatoes tha t rot ted in the field were affected with scab.

Since a reaction around pH 5.5 or 5.6 appears to be approach- ing the limit for the production of scab-free potatoes of the Green Mountain variety on this soil, it is interest ing to note how fa r this reaction is f rom ideal for the best growth of some other crops. In an adjoining field where an application of hydra ted lime at the ra te of 2000 pounds per acre had changed the reaction f rom pH 5.4 to 6.1, the yield of green peas was increased 8.6 per cent, the growth of peas and vines 13.3 per cent; the total weight of table beets increased 108.7 per cent; the weight of the tr im- med beets was increased 135.9 per cent and spinach was in- creased 139.4 per cent. Cauliflower, which followed these crops, gave an increase of 88 per cent in the number of heads cut where the acidity had been reduced. These figures, which in the case of the beets and spinach would be even more impressive if the acidity had been fur ther reduced, show the need of changing the reaction of this soil for these more sensitive crops and emphasize the difficulty of including any of them in rotat ions with potatoes.

Maintaining the soil acidity at a point favorable to the produc- tion of scab-free potatoes also increases the difficulty of supply- ing the soil with organic mat ter . Rye is the principal cover crop used a f t e r late potatoes in this section. This will grow well even on land too acid for the best growth of potatoes. The legumes tha t might be used are limited because of the lateness of the sea- son when they must be sown. Ha i ry vetch is used to some ex- tent and while it will g row on this soil with a reaction of pH 5.2

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it does much be t te r where the reaction is less acid. Where the reaction is much more acid than pH 5.8 it appears to be neces- sary to inoculate each year, as very few nodules are found the second year even where the roots were well supplied with nod- ules the previous season.

This experiment has not been running long enough to warran t any very definite recommendations, but it does indicate tha t it may be desirable to reduce the soil acidity as much as is con- sis tent with the production of scab-free potatoes. Such adjust- ment mus t be based upon a knowledge of the soil reaction and of the amounts of lime or o ther substances needed to bring about fair ly definite changes.

Recent Studies on Potato Seed Disinfection

By F R E E M A N WEISS . B u r e a u P l an t I ndus t ry , U. S. D e p a r t m e n t of Agr icul ture , Wash ing ton , D. C.

As seed disinfection is a part icularly t imely subject in the spring, it is proposed to devote the pathology section of several numbers of this journal to present ing br ief reports on recent experiments with potato seed t rea tments so far as the investi- gators are willing to make public their results and preliminary conclusions. In this series of reports it is aimed to discuss the present s ta tus of such questions as the comparat ive efficiency of the old s tandard t reatments , the hot formaldehyde method, and the new mercury products, in the control of black scurf and scab; also the value of the "insoluble" mercury coatings in the prevention of seed-piece infection f rom the soil, and the i r effect on corking-over of cut seed, st imulation of root g rowth and germination.

No a t t empt will be made now to summarize the results or to draw conclusions, but these reports can be regarded as the test i- mony of a number of witnesses whose individual stories are in- complete but whose collective evidence will afford growers about all tha t is yet known of the subject .

1. G E N E R A L

Disinfection of seed potatoes was one of the earliest applica- tions of antiseptics to the control of plant diseases, having been introduced ~n 1890 by borrowing f rom medical practice the use of bichloride of mercury, and it was first successfully employed