76 



EFFECT OF PHOSPHATES 



Tree Field, Cockle Park, has resulted in a considerable increase in 

 the nitrogen content of the soil. In 1908 the percentage of nitrogen 

 in the soil receiving phosphates was -236 %, whereas the untreated 

 soil contained only -185 %. 



From analyses of the Tree Field soils in 1919 the results shown in 

 Table XL were obtained. 



TABLE XL. PERCENTAGE OF NITROGEN IN THE SOIL 

 OF TREE FIELD, COCKLE PARK 



Analyses of the soil at the various Essex experimental centres after 

 intervals of four, three and two years show that the gain in nitrogen 

 on the plots receiving phosphates is considerable. The results are 

 given in Table XLI. 



TABLE XLI. PERCENTAGE OF NITROGEN IN FIRST 9 INCHES OF SOIL 



Average of 8 plots. 



f Average of 2 plots. 



At Horndon samples were withdrawn from several of the plots in 

 order to ascertain whether there was any difference in the influence 

 of the various phosphates on the collection of nitrogen by the nodule 

 organisms. The figures are set out in Table XLII. 



The sampling errors are probably considerable, and it would be 

 unfair to argue too much from the comparison of one plot with 

 another. If, however, the various rock phosphate plots are grouped 

 together, the two basic slag plots, and the two untreated plots, more 

 reliable data are obtained, as appears in the lower part of Table XLII. 



