YIELD 



419 



Climate. That an adequate temperature, a certain light intensity, and 

 a suitable supply of water are essential conditions for the growth of all 

 crops is well understood, but the influence of variations in each of these 

 factors upon the yield of the wheat crop has not been exactly investi- 

 gated. 



The highest yields of wheat are only obtained in districts where the 

 mean winter temperature is comparatively high, the rainfall 20 to 30 

 inches during the growing season, and bright warm weather at the time 

 of the development and ripening of the grain. 



It is well known among the agriculturists of this country that an ex- 

 cessive rainfall during the winter is disastrous to the yield of autumn- 

 sown wheat, and especially so where the sowing has been delayed. The 

 root-system and the young shoots of the plants are seriously checked in 

 their development, doubtless by the want of adequate aeration of the 

 water-logged soil and the loss of soluble food constituents in the drainage. 



It has been remarked by many observant farmers of the last two 

 centuries that upon the same farm in one season the yield per acre has 

 sometimes been 30 bushels, while in other seasons upon the same fields 

 with similar cultivation, manuring, and general treatment of the crop, the 

 return has been less than 20 bushels. 



In Great Britain the best season of last century was 1863, when the 

 wheat crops throughout the country were extraordinarily good : the worst 

 was 1879, when the yield was estimated at less than half the average. 



The difference between these seasons is strikingly illustrated by the 

 returns, given below, of the wheat crop upon several plots at Rothamsted 

 which have received the same manures and general cultivation annually 

 for over sixty years. 



YIELD OF GRAIN PER ACRE 



In 1863 the winter and early spring were extremely mild, with a rain- 

 fall below the average. In the growing season of the early summer there 

 was abundant rain, followed by dry weather in June and July up to harvest. 



