'218 NEBRASKA STATE HORTICULTURAL SOCIETY 



peratures. This method has not been found entirely practical, however. 

 Tubers that form deep in the ground are much more difficult to dig with- 

 'out injury. It was though that possibly hilling up the rows with soil at 

 the last cultivation, as used to be practiced with potatoes, might be an ad- 

 vantage in the same way; but it has been known for a long time that, 

 while hilling up may be good in itself, it is impossible to produce a 

 •ridge about the potato plants without getting the dirt from the middle 

 X)t the rows, and in doing this a large number of potato roots are cut and 

 Ihe yield is likely to suffer materially. The only other method of ac- 

 vjomplishing what was desired that has suggested itself to me is the use 

 of a mulch of straw, old hay, or other coarse material. This litter mulch 

 can be spread over the surface of the ground, either before the plants 

 come up or after they have reached considerable size. It has been found 

 that a straw mulch four inches deep after settling keeps the soil tem- 

 perature a few inches under it almost constant from day to night and 

 constant within a few degrees from week to week during the summer. 

 On the whole, also, the average soil temperature is considerably lower 

 under the mulch than when bare. The temperature of the air immediate- 

 ly above the mulch, however, fluctuates much more decidedly than it does 

 .above bare ground. It is not uncommon to get temperatures from three 

 to five degrees lower at night just above the surface of a mulch than just 

 above the surface of bare ground similarly located. During the hottest 

 i)art of the day, on the other hand, the temperature immediately above the 

 mulch reaches a point from three to five degrees higher than that above 

 bare ground in the same situation. Potatoes grown by means of a straw 

 mulch then have their roots and the tubers subjected to rather low and 

 very uniform temperatures and their tops to high and particularly to 

 extremely variable temperatures. The mulch, except in protracted dry 

 periods, retains moisture in the soil better than ordinary cultivation, so 

 that the plant has the advantage of a higher percentage of moisture and 

 .a more uniform moisture content. 



Under these conditions cf temperature and moisture, potatoes grown 

 at the Eperiment Station have yielded on the average fully as good crops 

 as when given good cultivation. It is true that in certain cases the yield 

 has been lessened materially, particularly where the stand has been hurt 

 by applying the mulch too deep before the plants came up or by planting 

 the seed tubers to deep so that the plants have lost vitality in pushing up 

 through both the soil and the straw. Where the stand has not been hurt 



and it is not usually hurt if the much is applied carefully, and never 



hurt if the mulch is applied after the plants are well up— the yield has 

 been fully as good as where the best cultivation was given. Mulching 

 with coarse stable manure has often increased the yield quite noticeably. 

 The important thing from the standpoint of this paper, however, is the 

 effect of the mulch upon the crop the following year. In every case this 

 •effect has been a favorable one. To show that the test was carried on 

 fairly, it may perhaps be well to out line it in some detail. 



