A STUDY OF FACTORS INFLUENCING THE YIELD OF POTATOES 1245 



results than ridging in North Dakota, even in sections having the heaviest 

 rainfall. 



Since the system of cultivation as well as the depth of planting may have 

 a part in determining the ultimate depth of the seed piece, this factor of 

 depth of seed piece should be controlled in all tests of the influence of system 

 of cultivation on yield. Woods and Bartlett (1909) and Woods (1911) 

 reported a comparison of the yields from shallow planting and high ridging 

 and from medium planting and medium ridging. In these tests the depth 

 of seed piece was constant. The medium-ridge culture gave a three- 

 years average yield of 10 bushels per acre more than the high-ridge culture. 

 Woods (1914), reporting a continuation of these tests but including deep 

 planting and level culture, showed a four-years average yield for the years 

 1910 to 1913, inclusive, of 276 bushels per acre from medium ridging, 261 

 bushels per acre from level culture, and 232 bushels per acre from high 

 ridging. Thus, over a long period of years, in a region of 'relatively high 

 rainfall and with the depth of seed piece constant, the yields favored a 

 system ranging from medium-ridge to leve.l culture. Because of the 

 greater difficulty of harvesting the crop from level culture, however, Woods 

 concluded that, for Maine conditions of soil and climate, there is little 

 choice between these three methods. 



Macoun (1905) reported four-years average yields, from level and from 

 ridge culture, favoring ridge culture by 22 bushels per acre. Level culture 

 proved the better in one of the four years, and, altho one of the four was 

 a drought year, this was not the year in which the level culture yielded 

 the best. Macoun's results were obtained at the Ottawa station, in a moist 

 sandy loam not subject to drying out. Zavitz (1916), in a nine-years 

 test, obtained an average difference of 7.6 bushels per acre in favor of ridge 

 culture. He stated that three of the nine years were comparatively dry, 

 and in these three years level culture gave the higher yields. Clinton 

 (1916), in a six-years comparison of ridge and level culture, obtained yields 

 slightly favoring ridge culture during three years and yields slightly favor- 

 ing level culture during the remaining three years. He concluded that 

 the only difference in the influence of these two systems on yield is in an 

 advantage from a lower percentage of blight rot under the ridge-culture 

 system. 



It must be concluded from the above review of experiments that, in 

 general, level culture has given slightly better yields than has ridging. 

 The advantage has been most marked in dry years and in the lighter 

 soils. Depending on regional soil type and seasonal rainfall, however, 

 the advantages generally conceded to ridging should be considered in choos- 

 ing the best system to fit a specific locality. 



Owing to the lack of variation in tillage methods within each of the 

 regions studied, it was not possible to correlate this factor with yield' by 

 survey methods. Altho some variation in the degree of ridging exists 



