46 Experiment Station Bulletin 367 



merit. In one block ammonium nitrate, calcium cyanide, ammonium sul- 

 phate, sodium nitrate, and Uramon (Urea) were used as N sources and 

 applied at the rate of 100 pounds of N per acre plus P2O5, 75 pounds, and 

 K 2 0, 45 pounds per acre. In other tests the N-P-K ratios were varied 

 from 0-2-1.75 to 4-2-1.25, the nitrogen varying from to 17, 35, 70, and 

 140 pounds per acre, with P and K remaining as given above. In further 

 tests the total pounds of N, P, K per acre were varied. In general, there 

 was an increase in the total fruits per plant with increases in nutrients 

 applied. As a result, the high fruit-to-leaf ratio was maintained, and de- 

 foliation was as heavy on these as on the checks. Although abundant soil 

 nutrients were available, a limited number of tissue tests did not reveal 

 increases of N, P, or K in the leaf petioles. 



M. C. Richards, R. C. Jones 



Factors Influencing the Development or 



Suppression of Leaf-Roll Symptoms in Potato Foliage 



From December to March, when days are short and cloudiness fre- 

  quent, the leaf-roll symptom can be masked in the Green Mountain va- 

 riety of potato grown in the greenhouse by adding to the soil certain soil 

 nutrients at planting time. When tubers with severe net necrosis were 

 planted in six-inch pots to which 11 grams of sodium nitrate or 8-16-16 

 fertilizer had been added, the leaf-roll symptom was absent in from 75 

 to 100 per cent of the plants. Plants from sections of the same tubers 

 planted in pots with 11 grams of superphosphates or potassium chloride 

 had well-developed symptoms in 87 to 100 per cent of the cases. Plants 

 in the pots containing nitrogen or complete fertilizer showed a higher 

 percentage of masking when the soil was kept relatively dry. The mask- 

 ing was less when the tests were repeated in April and May, and no mask- 

 ing occurred when similar tests were made in the field during the sum- 

 mer. There appears to be a relationship between light conditions and 

 nitrogen nutrients with respect to the suppression of the leaf-roll symp- 

 tom in the Green Mountain potato. 



M. C. Richards, Stuart Dunn, R. C. Jones 



POULTRY 



Protein Requirement of Chickens at Various 

 Stages of Growth and Development 



It has been possible during the year to complete the study involving 

 the pH of the gastro-intestinal tract. This study was deferred during the 

 war emergency. To obtain data on the normal pH of the digestive tract 

 pH determinations were taken on individual chickens at three- and four- 

 day intervals from age 16 days to 101 days. From 101 to 164 days of age, 

 the pH was taken at seven-day intervals. Seven or more chickens were 

 used for each set of determinations. The digestive tract was divided into 

 10 parts and a minimum of two readings was taken on each part. There 

 were used 247 chickens of which 116 were males and 131 were females. A 



