Corn Groivers' Association. 165 



Missouri^ and our lands are showing a decreased productiveness 

 primarily because of the lack of humus and of nitrogen. The 

 building up of the humus is, therefore, the first and most funda- 

 mental principle that must be adopted in a constructive system of 

 agriculture. 



A second general feature which characterizes practically all 

 Missouri soils is a deficiency of phosphorus. This lack is an 

 inherent one, due to the character of the rocks from which the 

 soils were formed, and to the methods of soil formation, rather 

 than our system of cropping. It is true that our constant grain 

 growing has tended to intensify this lack, especially through the 

 removal of the available portion, and it is, therefore, the deficiency 

 in available phosphorus, rather than a lack in the total phosphorus 

 supply, that is limiting our crop production. The fact that the 

 best system of agriculture we can adopt still tends to a gradual 

 loss of phosphorus through the bones of animals as they are sold 

 will, doubtless, sooner or later, drive us to the returning of some 

 phosphorus to our soil in a commercial form, and in many parts 

 of the State this practice is already highly remunerative. 



The potassium is abundant in practically all Missouri soils 

 excepting those of the Ozark upland, and it is simply necessary 

 to practice the proper system of agriculture to make it available 

 and to maintain it indefinitely. The feeding of crops, the main- 

 tenance of a high humus content, good drainage and proper culti- 

 vation will maintain the available potassium supply practically 

 indefinitely except in some of the Ozark uplands mentioned and 

 on certain of the more sandy soils of the State. 



The lime content is also sufficiently high for the present, in 

 most cases, and thus far only rather limited areas — notably those 

 of the flat prairie land of Southwest Missouri and some of tha 

 Ozark uplands — seem to be in need of this element. Any intensive 

 system of agriculture tends to a gradual removal of the lime con- 

 tent of the soil, but most Missouri lands are sufficiently well 

 supplied to obviate the necessity for its use for a considerable time 

 to come. 



METHODS OF MAINTAINING FERTILITY — CROP ROTATION. 



The first essential to any rational constructive system of agri- 

 culture is a more or less systematic crop rotation. The following 

 table shows the results of seventeen years' cropping of the upland 

 soil at the Missouri Experiment Station under different systems: 



