An Agricultural Testament by Albert Howard

GREEN-MANURING

Since Schultz-Lupitz first showed about 1880 how the open sandy soils of North Germany could be improved in texture and in fertility by the incorporation of a green crop of lupine, the possibilities of this method of enriching the land have been thoroughly explored by the Experiment Stations. After the role of the nodules on the roots of leguminous plants in the fixation of atmospheric nitrogen was proved, the problems of green-manuring naturally centred round the utilization of the leguminous crop in adding to the store of combined nitrogen and organic matter in the soil. At the end of the nineteenth century it seemed so easy, by merely turning in a leguminous crop, to settle at one stroke and in a very economical fashion the great problem of maintaining soil fertility. At the expenditure of a little trouble, the leguminous nodule might be used as a nitrogen factory while the remainder of the crop could provide humus. All this might be accomplished at small expense and without any serious interference with ordinary cropping. These expectations, a natural legacy of the NPK mentality, have led to innumerable green-manuring experiments all over the world with practically every species of leguminous crop. In a few cases, particularly in open, well-aerated soils where the rainfall after the ploughing in of the green crop was well distributed and ample time was given for decay, the results have been satisfactory. In the majority of cases, however, they have been disappointing. It will be useful, therefore, to examine the whole subject and to determine if possible the reasons why this method of improving the fertility of the soil seems so often to have failed.