FERTILIZER TESTS ON PASTURES 11 



nutrients, especially nitrogen, may limit growth. This statement applies par- 

 ticularly to vegetation composed mainly of grasses. As shown by the data, in 

 good "clover years" white clover may grow luxuriantly on plots receiving only 

 minerals (L, P, K); but, as shown in an earlier bulletin (1) "clover years" are 

 irregular and uncertain in occurrence, and not understood as to cause. 



The effect of lime in increasing the ready availability of applied phosphorus is 

 shown by the data of Table 8. This is especially well shown by the 2P and 3P 

 treatments in comparison with the same treatments plus lime. No doubt, one of 

 the principal benefits of lime in pasture improvement is this effect on availability 

 of phosphorus. 



Table 8. — Effect of Phosphate and Lime Applications on Amount of 

 Readily Available Phosphorus in the Amherst Pasture Soil* 



Pounds Available P per Acre 

 Air-dry Soil 



First 4" Second 4" 



P 56 36 



P, L 42 42 



2P 108 56 



2P, 2L 166 110 



3P 232 78 



3P, 3L 392 208 



*Method of Truog. 



The recent publication of Brown (2) shows that fertilizer nitrogen (nitrate of 

 soda and other carriers used) and lime, independently of each other increased 

 the effectiveness of phosphorus; nitrogen more than lime. Midgeley (4) showed 

 that sodium nitrate greatly increased the penetrability of phosphorus in soils. 

 A determination of readih' available phosphorus in soils which received no nitrate 

 and the corresponding treatment with nitrate, Amherst experiment, showed 

 slightly more available phosphorus in the nitrated plots. More phosphorus was 

 removed from the nitrated plot in its larger crop. There is therefore, some evidence 

 from this experiment that sodium nitrate is of considerable indirect value because 

 of its effect on the axailability of the phosphorus. 



Summary 



Results of top-dressing with chemical fertilizers experimental fields on two 

 soil types are reported in this bulletin. The principal results are as follows: 



1. In the Worcester experiments, with the exception of phosphorus, the 

 effects of the different added nutrients were mainly cumulative. 



2. The net mean increase due to phosphorus was 20 pounds dry material; 

 to potassium 343 pounds; to nitrogen 556 pounds; and to calcium (as limestone) 

 230 pounds per acre. 



