The nitrogen balance in cultivated semi-arid western Kansas soils

The nitrogen content of 99 plats, located at three different points in semi-arid western Kansas, was determined in 1916 and again in 1927 and 1928. The quantities of nitrogen found at both analyses, together with the treatments to which the plats have been subjected, are reported in this paper. These data would seem to indicate the following relative to the nitrogen changes taking place in these soils during this short period of time: 1. Very large losses of nitrogen may take place under certain conditions. 2. The principal factor governing the nitrogen balance for this period seems to have been the nitrogen content of the soil at the beginning of the period. A correlation coefficient of 0.64 +/- 0.04 was found between the original nitrogen content and changes taking place in the nitrogen content for the entire 99 plats, or for 38 similarly cropped plats the corresponding value was 0.747 +/- 0.048. 3. Of the various cropping systems compared, continuous small grain or alternate small grain and fallow seemed to be conducive of the smallest changes in nitrogen content. One year of grain and three years of fallow apparently induced very large losses. Sorghums (kafir and milo), either continuous or alternating with fallow, also caused relatively large losses. The data relative to the influence of the various rotations are less conclusive, being complicated by the influence of the nitrogen content of the soil at the beginning, but on the average the losses were much greater than for small grain alone and less than for the sorghums. Losses when stable manure was added in a rotation were very high in spite of the nitrogen added in the manure, but again the influence of the original nitrogen content was probably partially responsible for such heavy losses. 4. There are indications that when the nitrogen content of the soil in this region falls to approximately 0.1% the factors responsible for additions of nitrogen to the soil will counterbalance those tending to cause its removal, thereby establishing a nitrogen equilibrium near this level. The very important question is raised whether at such a low nitrogen level the soil will be able to supply an adequate quantity of soluble nitrogen to enable the maximum utilization of the available moisture.