applied at the rate of 74 kilograms per hectare, yield was markedly 

 increased by additions of nitrogen up to 336 kilograms per hectare. The 

 yield produced by 672 kilograms per hectare of nitrogen was not signifi- 

 cantly greater than that where 336 kilograms per hectare were applied 

 during the first growing season. 



nR'=.80 



Y= 2978.8 + 28.7X- 0.024 X 2 , 



aR 2 = .87 



a 



"y=5555.8 + 11.37X-0.0107X 2 , 



■ o R 2 = 78 



^^^ """°~?=4412.1 + 8.72X-0.009X 2 



..-* °. <* *>R 2 = .40 (ns) 



t- O 



oNo P 



a 74 kg/ha P 



1971 



1972 



336 

 Nitrogen ( kg /ha/yr 



672 



Effect of nitrogen and phosphorus fertilizers on 

 yields during two successive growing seasons. 



During the second growing season, higher yields and a greater response 

 to fertilization was attained (Figs. 56 and 57). When phosphorus was 

 supplied, the rate of yield increase did not level off beyond 336 kilograms 

 per hectare of nitrogen as in the first year, but was linear over the range 

 of nitrogen rates applied. There was also an increase in the difference 

 between yields of no phosphorus and phosphorus treatments, indicating 

 phosphorus became severely limiting during the second year as yields 

 increased. 



125 



