58 THE CHEMISTRY OF THE FARM. 



These losses assume that the farmyard manure is 

 properly made, and returned to the land without waste. 

 If the manure has suffered loss by drainage the estimates 

 given would have to be increased. 



The loss of potash is extremely small, and may gene- 

 rally be quite disregarded. If, however, no cake is used, 

 and the land is poor in potash, the loss might be replaced 

 by the use of 1 cwt. of calcined kainit for the seeds. 



The loss of phosphoric acid would be more than re- 

 placed, even if no cake were employed, by the use of 2 

 cwt. of superphosphate for the swedes. 



The loss of nitrogen by the sale of crops and meat is 

 seen to be far more considerable than the loss of phos- 

 phoric acid or potash. The figures given are also below 

 the truth, as they do not take into account the nitrates 

 lost to the soil by drainage. Against this loss of nitrogen 

 we have to place the amount annually supplied to the 

 land by the rainfall, say 6 — 8 lb. per acre, and also the 

 unknown quantity absorbed as ammonia from the atmo- 

 sphere by soil and plant ; this latter amount will vary with 

 the nature of the soil and climate, and probably also with 

 the character of the cropping. We may, however, safely 

 assume that with the cropping and manuring supposed in 

 the preceding table the total gain of nitrogen from the 

 atmosphere will balance the loss, so that under good 

 management the rotation might be indefinitely continued 

 without diminishing the fertility of the land. 



In the four-course manured rotation upon the heavy 

 land at Kothamsted, the nitrogen annually removed in the 

 crops, on an average of thirty-two years, has exceeded by 

 about 35 lb. the quantity supplied in the manure. If the 

 crops on this experimental rotation should be permanently 



