Field Experiments on Root- Crops. 511 



We learn from the preceding experiments that whilst super- 

 phosphate alone doubled the produce, crude potash-salts alone 

 gave no appreciable increase. The addition of these salts to 

 superphosphate increased as little the efficacy of the phosphatic 

 manures as that of common salt. This possibly may be a case 

 in point, of the potash failing because the soil was poor in 

 elements of fertility other than potash, as stated in page 505. 



The roots on the plot dressed with salt weighed about 12 cwts. 

 less per acre than those grown on the unmanured part of the 

 field. This difference, however, falls within the range of the 

 natural variations in the productive powers of adjoining strips of 

 the same field. Indeed, the difference in the produce of plots 1 

 and 7, both manured with 3 cwts. of superphosphate, is much 

 greater than the decrease on plot 5. 



The want of success here experienced with potash-salts and 

 common salt is the more surprising, since common salts applied 

 to mangolds grown on the same land in previous years con- 

 siderably increased that crop. It may have arisen in part from 

 the late date at which the swedes were sown, or yet more from 

 the circumstance that the saline manures were sown broadcast 

 just before drilling the seed, for Mr. Kimber informs me that 

 they visibly checked the growth of the young plants. Where no 

 superphosphate was applied, the young plants never got a fair 

 start ; where it alone was applied, the crop was as good, if not 

 better than where the addition of potash-salts or common salt 

 was made. 



Since saline matters certainly check the growth of the turnip 

 plant in its earliest stages of existence, even on land on which 

 such manures might be beneficial, if applied under more favour- 

 able conditions, two courses are open to us in their use : — 

 either to make the application quite early in spring, say towards 

 the end of February, or to delay it until the plants are singled, 

 in a vigorously growing condition. The early application of 

 salt will secure its general diffusion through a large mass of soil ; 

 but, on the other hand, if the early spring months should be very 

 wet, most of the salt undoubtedly would be washed away, for 

 though all soils have the power, some in smaller, others in greater 

 degree, to absorb and retain potash, ammonia, or phosphoric 

 acid from soluble fertilising matters, they do not exert such 

 a power on soda-salts, and allow consequently common salt to 

 pass away with the drainage water. 



If the application of salt to root-crops be delayed until the 

 plants are singled and in a vigorous state of growth, and little 

 or no rain falls afterwards, the roots certainly will not be 

 benefited by the salt; nevertheless, on the average of seasons 

 I am inclined to think it the better plan to sow the salt broad- 



