>9 



THE GREEN MANURING EXPERIMENT. 



Throughout the Rothamsted experiments a number of observa- 

 tions have shown the marked effect of ploughing-in a green crop or 

 a crop residue as a preparation for a succeeding crop. Every four 

 years the residues of a clover crop after carting the hay are ploughed- 

 in on half of the Agdell Field, and the effect on the succeeding 

 crops in the rotation is recorded. In Hoos Field some leguminous 

 crop has periodically been ploughed-in and a number of grain crops 

 have then been grown, almost always with beneficial results. 



The growing scarcity of stable manure renders it imperative 

 that some method should be worked out whereby the farmer 

 can get all the benefit of stable manure in some other way, and 

 green manuring affords an obvious means of doing this. Ex- 

 periments in the laboratory and pot culture house, however, showed 

 that the growing plant has a complex effect on the soil and on 

 other crops, and that one could not without further trial advocate 

 unrestricted green manuring. For example, it was found that the 

 growing plant apparently depressed nitrification and other bacterial 

 actions in the soil, and that some interval was needed between two 

 crops in order that tin- bacterial processes might become completed. 



Another action is indicated as the result of Mr. Pickering's 

 work at Woburn : one growing crop his an injurious effect on 

 another growing crop apparently through exerting some deleterious 

 influence on the soil. It appears, therefore, that there is another 

 side to the question, and that a growing crop not only takes out 

 certain plant foods (which are automatically returned when the crop 

 is ploughed-in, or can be added as artificial fertilisers), but it may 

 also have other effects. This is while it is actually growing: the 

 residues ploughed-in seem to be wholly beneficial — at any rate no 

 ill-effect has yet been detected in the field, although one (a destruc- 

 tion of nitrate in certain circumstances) has been indicated in the 

 laboratory. So far as our present knowledge goes the best results 

 are only attained when a period of fallow comes after the green 

 manure crop. 



Thus green manuring is intimately bound up with fallowing. 

 It was shown in the last Report that fallowing had a very beneficial 

 effect on the crop of barley and further observations to the same 

 effect have been made this year. Winter oats on Sawpit Field taken 

 after a fallow were better than crops fertilised with nitrogenous 

 manures. No green manure or crop residue was ploughed in either 

 for the bailey or oats, but this year an experiment was made to 

 find the effect of combined crop residues and fallow on wheat. 

 A four-year-old lucerne ley on P>roadbalk Field was broken up, 

 fallowed during the hot w r eather and sown with wheat in October, 

 1913. The land had received no manure for some years, but the 

 wheat crop was greater than on any plot receiving artificial 

 manures, and at least as large as that on plot receiving 14 tons of 

 farmyard manure. Even more remarkable, however, was the 

 effect on the weight of the grain. Practically all the wheat on the 

 regular plots with the exception of the unmanured had the same 

 density, viz. : 62' 2 lbs. per bushel, this being independent of the 

 amount or nature of the fertiliser used. The wheat after lucerne 

 had a heavier grain, weighing 63*9 lbs. per bushel. 



