138 LIVING ORGANISMS OF THE SOIL [chap. 



fair level of fertility is being maintained through the 

 nitrogen collected by the growth of clover once during 

 each four-year cycle. 



All these illustrations serve to emphasise the point, 

 that by the growth of leguminous plants as frequently 

 as possible the farmer possesses a means of maintaining 

 and even increasing the stock of nitrogen in his land 

 without expense, because the crop of valuable fodder 

 produced in itself pays for the year's farming. Of the 

 crops commonly grown, lucerne (or alfalfa) seems to be 

 the most effective in fixing nitrogen ; it is particularly 

 valuable on poor chalky and sandy soils where it can be 

 left down for several years, when it will with a minimum 

 of expense both yield a paying amount of fodder and 

 prepare the land to carry a short succession of arable 

 crops with no extraneous nitrogen supply. Lucerne has 

 proved more difficult to establish on the poor clays, but 

 even there its benefits are very marked. Sainfoin is 

 probably as valuable a nitrogen collector, but it has been 

 less rigorously tested ; while the clovers, particularly red 

 clover, are especially effective considering the short 

 time they occupy the soil. Red clover is most valuable 

 to the soil if it is kept grazed after the first cut ; a second 

 cut leaves less nitrogen behind, because in the late summer 

 the nodules on the roots become considerably depleted of 

 the nitrogen previously gathered from the atmosphere 

 in order to make the second growth, while a crop of 

 clover seed is even more exhaustive of anything that 

 may have been stored in the root. The annual 

 leguminous plants — beans and vetches — gather less 

 nitrogen from the atmosphere, and are therefore less 

 valuable as preparations for succeeding crops ; indeed, 

 on the rotation field at Rothamsted, a bean crop has 

 proved no better preparation for wheat than a summer 

 of bare fallow. At Rothamsted, however, the beans are 



