SWEET CLOVER: GROWING THE CROP. 17 



Soil types which have slightly acid surface soils and alkaline sub- 

 soils will grow sweet clover successfully, provided the acid soil is 

 not more than 6 to 1'2 inches in depth. 



FERTILIZERS. 



Owing to the fact that sweet clover thrives on the barren Selma 

 chalk (rotten-limestone) hills of Alabama and Mississippi and grows 

 abundantly on worn-out, abandoned land in north-central Kentucky, 

 it is often assumed that it will grow on soils too depleted in plant 

 food to produce other crops. These regions represent soils which 

 have become exhausted primarily in nitrogen and humus as the re- 

 sult of continuous cropping with nonleguminous plants. Some of 

 these soils contain sufficient phosphorus and potassium for fair crop 

 production, although this supply may be in such a condition that it 

 will not become available fast enough to supply the needs of most 

 crops. Sweet clover, like all legumes, has the power to extract nitro- 

 gen from the atmosphere, and on account of its extensive root system 

 it is able to obtain phosphorus and potassium from a larger area 

 than most plants. The large roots not only add a quantity of humus 

 and nitrogen to the soil but they also open it up to a considerable 

 depth, thus providing better aeration and improving its physical 

 condition. Improved physical condition causes the bacterial flora to 

 increase and thereby indirectly causes a larger quantity of unavail- 

 able phosphorus and potassium to be made available for plant use. 



On soils which are known to be low in phosphorus or potassium 

 an application of fertilizer containing the necessary element should 

 be made when sweet clover is sown without a nurse crop. However, 

 when it is sown with a nurse crop or in the late summer or early fall 

 on grain stubble, the residues left in the soil from fertilizers applied 

 to the nurse crop will, under ordinary conditions, be sufficient for 

 the plants. That sweet clover will respond readily to applications 

 of phosphorus on soils low in this element has been well demonstrated 

 by the farmers of Livingston County, 111. In this county finely 

 ground rock phosphate was applied to a portion of a number of 

 fields at the rate of 1.500 to 2.000 pounds per acre. The phosphate 

 \vas thoroughly incorporated with the soil just before seeding oats 

 and sweet clover. In the growth of sweet clover there was a marked 

 difference the following year between the treated and untreated por- 

 tions of the fields. Those portions of the fields which received an 

 application of phosphate not only contained many more plants on a 

 given area, but the vigor and growth of the plants were most marked. 

 On June 1 the plants on the treated areas were 12 to 15 inches taller 

 than those on the untreated parts of the fields. This difference in 

 74950 Bull. 79717 3 



