MAINTAINING THE ORGANIC MATTER OF SOILS 159 



soils it lias been so completely removed that they are acid and the 

 element calcium is too deficient to produce good crops, especially 

 of legumes. Applications should be made once in every rotation. 

 To maintain the limestone at present prices costs from fifty cents 

 to one dollar per acre per annum pins the cost of applying it. 

 This will make possible the growing of legumes for soil-renovating 

 purposes. On eroded hill land large growths of sweet clover 

 amounting to 2.7 tons per acre for the two years of its growth 



Fio. 80. Clover on gray silt loam on tight clay. (Marion silt loam.) Manure gave 

 0.0 ton of gratis with practically no clover, while immure with rock phosphate ami limestone 

 gave 2.05 tons of good clean clover hay. (Illinois Station.) 



were made possible by the application of four tons of limestone 

 to acid soil. 



2. By Applications of Phosphorus. Phosphorus should be 

 mentioned in this connection because so many soils arc deficient in 

 this element, and its application is very necessary for increasing 

 the growth of legumes. It often more than doubles the growth of 

 clovers and, of course, gives a larger amount of much-needed active 

 material to be turned under. The acids formed in the decay of 

 organic matter aid greatly in the liberation of phosphorus and 

 potassium that are locked up in the minerals in the soil. The 

 average increase of clover at the Illinois Station at Urbana on 

 brown silt loam was 1.05 tons per acre where phosphorus was uscrl. 

 while on another field on the same type the increase was 1.r>l tons. 



