98 RESPONSE TO FARMYARD MANURE 



to other materials a dressing of phosphoric acid and potash equivalent 

 to about 72 Ibs. of each per acre. This amount of phosphoric acid 

 was presumably sufficient to meet the requirements of the 1920 

 season, and it is therefore interesting to note what effect the dressing 

 of potash had 1 . 



There was no doubt throughout the whole season that the farm- 

 yard manure plot was the best on the field. For the first time that 

 portion of the field not within the experimental area, and which had 

 received a similar dressing of dung, looked better and bore a better 

 crop than the experimental plots. 



The average weight of hay on the phosphate plots was 31-8 cwts. 

 per acre, and on the plot receiving a small dressing of phosphates 

 and potash in the form of dung 40-3 cwts., leaving a gain of 8-5 cwts. 

 per acre which can only be attributed to potash. 



During the whole season the plots were inspected once a week, 

 and it was early evident that the clover was making a more vigorous 

 growth on the farmyard manure plot. Owing to an oversight a 

 sample of hay was not removed from this plot for botanical analysis. 



The aftermath was allowed to grow until the beginning of October, 

 and not only was there a more vigorous growth, but the bottom of 

 clover on the farmyard manure plot was closer and more regular 

 than on any of the other plots. 



In view of the evidence there can be little doubt that on this 

 type of soil, after the need for phosphate has been met, potash is the 

 second limiting mammal factor. Moreover it is very probable that 

 in all but the exceptionally dry years a profitable return from the 

 application of potash will be secured. It should be possible by 

 judicious application of phosphates and potash to raise the produc- 

 tion of meadow hay to the 2 tons an acre level in all but exceptionally 

 dry years. 



Such results serve to confirm the conclusion that potash is the 

 second limiting manurial factor at Hassobury and Farnham, and 

 they incidentally suggest that on grass-land in Essex profitable results 

 from the application of potash are likely to accrue when the soil 

 contains less than -03 % available potash a figure considerably 

 above Dyer's limit. 



1 It is very improbable in view of the particularly moist season that the organic 

 matter or the nitrogen in the farmyard manure plot had any effect on the yield of 

 hay. The meadow has been down to grass for at least 80 years, and a large store of 

 organic matter and nitrogen has been accumulated. The action of lime would pre- 

 sumably be to release these materials for the plant, and the lack of response to the 

 application of lime suggests that the soil can normally provide all the nitrogen the 

 crop requires in a suitable form. 



