38 University of New Hampshire [Sta. Bull. 324 



a high phosphorus treatment showed least loss in organic carbon, while 

 the omission of phosphorus from Lane farm resulted in a loss of organic 

 carbon more than double that from the high phosphorus treatment. In 

 view of the importance of soil organic matter in increasing infiltration and 

 preventing erosion, and because of accelerated erosion on many potato 

 farms of the state, this phase of the work demands and will receive fur- 

 ther study. 



Liming had a favorable effect on the organic carbon level, actuallv in- 

 creasing it on Lane and showing less decrease than certain other treat- 

 ments on Jackson farm. 



Because of the favorable effect of lime on the maintenance of organic 

 matter and in view of scab dangers from its use, it seems logical to con- 

 clude that lime should be used only in guarded amounts of 500, or not 

 more than 1000 pounds per acre on soils that have reached or are below 

 pH 5.0 in reaction. An accurate soil test along with the behavior of clover 

 and other crops grown in rotation should always be used as a guide before 

 lime is applied to the soil in a potato rotation. 



Specific Gravity Test for Potato Quality 



Literature covering the relationship between the specific gravity of 

 potatoes and their starch content is reviewed. It shows that starch con- 

 tent may be determined to \\ithin one or two per cent by determining the 

 specific gravity of the tubers in question. This is substantiated by actual 

 starch determinations of potatoes having a known specific gravity. 



Since the starch content of a potato is definitely associated with meal- 

 iness, it is concluded that the method of rapidly determining the specific 

 gravity of potatoes by immersing them in salt solutions of different strengths 

 may be used as a means of arriving at an estimation of potato quality. 



b'rom the tests which have been made and reported it seems apparent 

 that fertilizers have a slight effect upon potato quality, high phosphorus 

 tending to increase and high potash tending to decrease quality ratings. 

 These tests show also that there are wide inherent differences in quality 

 ratings among varieties, some varieties ranking high and others uniformly 

 low. Date of planting, the maturity of the tubers at harvest, and climatic 

 factors all play their part in affecting the quality ratings of potatoes within 

 a variety. Potatoes that are well matured before harvest, and especially 

 those which have been grown without any setbacks in midseason due to 

 adverse weather exhibit high quality. Variations in quality ratings of 

 potatoes grown in the same hill are as yet unexplained. 



Because of varietal differences noted it is felt that breeding may in 

 the future play a large part in increasing quality ratings. .\t the present 

 time, the wisest course for the farmer seems to jioint to using a well- 

 balanced fertilizer designed to promote maturity, and to plant his crop at 

 a time when it is least likely to be affected by midsummer drouth or heat. 

 A controlled water supply would undoubtedly help in this respect. A 

 study of the causes of difTerences in (|uality tliat exist among potatoes in 

 the same hill may or may not throw further light on methods of pro- 

 cedure whereby the average quality rating will be increased. 



