54 MASS. EXPERIMENT STATION BULLETIN 196. 



but I desire to point out that a little variation in level and character of 

 soil from the north to south perhaps helps to account for the relatively 

 high standing of N on plot 5. 



We have yet, however, to consider how the superiority of S on the 

 other plots, 1, 2, 3, and 4, can be accounted for. It seems to me possible 

 that variation in humus content produced by the different methods of 

 handling the manure and consequent differences in soU temperatures or in 

 biological activities going on in the soil may to some extent have in- 

 fluenced the results. I beUeve, however, that more important than 

 these is probably tliis fact, which, as was pointed out again and again by 

 Paul Wagner in connection with his different experiments a considerable 

 number of years ago, had an important connection with results.^ Wagner 

 pointed out that in northern latitudes optimum weather conditions for 

 growth may exist during only a small proportion of the so-caUed growing 

 season. This fact is generally recognized. All those familiar with agri- 

 culture in Massachusetts understand that, especially for crops flourishing 

 at high temperatures and to a considerable extent for others also, 

 weather conditions during some part of the growing season are unfavor- 

 able to rapid progress. It is often too wet or too dry, or it may be too 

 cold, and rather exceptionally too hot when the liigh temperature is 

 coincident with shortage in supply of moisture. When optimum weather 

 conditions come, then the plant is capable of extremely rapid growth, 

 provided the other factors essential for such growth exist, and among 

 such other factors an abundant supply of plant food is one of the most 

 important. Where the supply of plant food is comparatively low or 

 meager the crop may become a good one if the weather and other con- 

 ditions for growth are favorable throughout the greater part of the grow- 

 ing season, but, in proportion as the best of weather exists only a portion 

 of the time, the crop will come to rapid maturity only where it finds a 

 great abundance of food. Considerable wastage evidently occurred where 

 the manure was spread in the winter. It is clear, therefore, that the 

 supply of food, and hence this one among the several factors essential to 

 rapid progress when the weather conditions are right was found in highest 

 degree on plots S. It has long been recognized that the farmer or gardener 

 who works his land intensively (under which term in this connection I 

 refer particularly to an abundant supply of available plant food) is less 

 unfavorably influenced by bad weather than the farmer or gardener whose 

 soils are relatively low in available plant food or poorly worked. 



The Relative Effects of the Two Systems on the Proportion of 

 Clover in Mixed Mowings. 

 Whenever the plots used in this experiment were put into mowing, a 

 mixture of timothy, red top and medium and alsike clovers was sown. 

 The field was in mowing in 1912 and 1913, the first two years of the 

 period under consideration, and it was noted that the proportion of 



> Paul Wagner: Zur Kali-Phosphat-Diingung nach Schultz-Lupitz, Darmstadt, 1889. a. 18 u. a. 



