1019] FIELD CROPS. 33 



Severe winterkilling during January and February resulted in low wheat 

 yields. Average yields following different cropping systems for the 7 years, 

 1911-1917, were 17.3 bu. in rotation with alfalfa 4 years and corn 2 years, 15.73 

 bu. in rotation with corn and cowpeas, 13.38 bu. in rotation with corn 2 years, 

 and 14.88 bu. when grown continuously. Wheat grown continuously without 

 manure produced 11.85 bu. per acre ii* 1917, as compared with 20.5 bu. follow- 

 ing annual applications of 2.5 tons of manure. Wheat grown in rotation was 

 little affected by the use of manure or commercial fertilizers. The latter re- 

 sulteil in higher yields for all plats continuously cropped to wheat. With phos- 

 phorus there was an increase in yield of wheat of 3.49 bu. per acre in the 3-year 

 rotation, and with a complete fertilizer 7.07 bu. A fertilizer mixture high in 

 phosphorus and containing some nitrogen is deemed best, while ix>tassivun has 

 failed to jjrove beneficial. 



While alfalfa yields were low, due to drought during the summer, that grown 

 in rotation produced considerably more than that grown continuously. Manure 

 applied at the rate of 5 tons per acre every 3 years resulted in an increase of 

 about 0.5 ton of hay in 1917. The use of commercial fertilizers resulted in in 

 creased yields in every case, but the increase due to potassium is said to be 

 negligible. An application of 180 lbs. of acid phosphate per acre on alfalfa 

 grown in rotation resulted in an average increase of 878.9 lbs. of hay since 1911, 

 while with a complete fertilizer there was an increase of 1,477.5 lbs. 



The highest yields of cowpea hay were secured on the plats receiving a com- 

 plete fertilizer and barnyard manure. 



In a rotation of alfalfa, Kafir corn, corn, and oats, the highest yield of 

 alfalfa , was secured from the plat receiving manure and rock phosphate. 

 Kafir corn on the check plat produced 18.1 bu. per acre, as compared with 23.8 

 bu. from the plat receiving fresh manure, 23.4 bu. from fresh manure and rock 

 phosphate, and 25.7 bu. from leached manure. 



The highest yields of wheat were secured froni the earliest preparation of 

 the seed bed, and, in the case of continuous cropping to wheat, from plats 

 plowed 7 in. deep. Nitrification varied with the amount of moisture available 

 in the soil during the period of seed-bed preparation, while the available mois- 

 ture supply appeared to be dependent upon the amount of weed growth. Dif- 

 ferent methods of seed-bed preparation had little if any effect upon the potential 

 efficiency of nitrate-forming organisms, differences in the rate of nitrification 

 being due to differences in the activity of the organisms concerned in the de- 

 composition of organic matter, these in turn being affected by environmental 

 conditions which retard their activity rather than by any differences in bacterial 

 flora. The principal environmental factors involved are said to be the distri- 

 bution of the organic matter and the availability of the moisture supply. 

 Nitrification was as great in the surface 3 in. of soil as in the 3- to 6-in. level, 

 while in the 6- to 12-in. layer it was less than in the upper layers. Determina- 

 tions of the amount of weed growth on late-prepared plats and of the nitrogen 

 content of the weeds led to the conclusion that nitrification was as rapid on 

 tiiese plats as on those receiving early tillage. Based on the average yields, 

 it is recommended that if wheat stubble can not be plowed at once after 

 harvest (July 15), the land should be double disked immediately and plowed 

 6 or 7 in. deep when convenient, but not later than early September, with suf- 

 ficient cultivation to keep down weeds, and produce a firm seed bed. 



Observations were made on the effect on the moisture content and nitrate 

 formation in clay, silt loam, and fine .sandy soil of maintaining a 3-in. culti- 

 vated mulch and a bare surface. In addition, weeds were allowed to grow 



