THE MARSHALL SILT LOAM. 7 



of the moisture which falls upon it. This moisture is stored within 

 the silty surface soil and maintained against downward percolation 

 by the heavy silty loam or silty clay subsoil in sufficient quantity 

 to satisfy the demands of such crops as Indian corn and oats, both 

 of which require unusually large amounts of soil moisture for the 

 production of maximum yields. 



In addition the surface soil is unusually well supplied with par- 

 tially decayed organic matter through the centuries of growth, 

 death, and partial decay of the prairie grasses which flourished over 

 its surface before agricultural occupation of the type was brought 

 about. At present the drainage of the type is adequate over prac- 

 tically all of its extent. Erosion is not a serious problem, except in 

 limited areas. The surface topography, the stone free character of 

 the soil, the absence of timber, have all rendered its occupation and 

 tillage easy. Thus the limitations upon the classes of crops which 

 may be grown, and even the limitations upon the yields secured, 

 are chiefly those of climatic surroundings and of efficiency in culti- 

 vation rather than those of the inherent properties of the soil itself. 



Within the more eastern extent of the Marshall silt loam the 

 annual precipitation amounts to 35 or 40 inches. This precipita- 

 tion occurs in such form and at such times as to be absorbed readily 

 by the soil and to be maintained for the ensuing growth of plants. 

 The amount of precipitation gradually declines westward across 

 the Missouri River, and only becomes deficient when the great 

 dry-farming region of western Nebraska and Kansas is reached. 

 This variation in precipitation, however, gives rise to variation in 

 the kinds of crops which may best be grown upon different portions 

 of the region occupied by the Marshall silt loam. In the more 

 eastern sections the general farming crops common to the tem- 

 perate portion of the humid region may all be grown to advantage. 

 Westward from the Missouri River, however, certain special crops 

 gradually replace the corn, wheat, oats, and grass of the more east- 

 ern region, and large areas of Kafir corn, of broom corn, of durum 

 wheat, and of emmer are coming to be raised upon the Marshall 

 silt loam in the central and western portions of Kansas and Nebraska. 

 These crops, more resistant to drought and better suited to dry 

 farming conditions, have permitted of the extension of profitable 

 agriculture far beyond the limits which, half a century ago, it was 

 supposed had been set by precipitation conditions upon the profit- 

 able agricultural occupation of the land. Similarly, the timothy 

 and clover of the more humid region is largely displaced by increas- 

 ing acreages of alfalfa grown upon the Marshall silt loam, as well as 

 upon other types of soil west of the Missouri River. This valuable 

 forage plant is coming to dominate the hay production upon the 

 Marshall silt loam not only in this more western region, but even 

 within the more humid portions of its development. 



