The relations among fertilizer treatment, soil moisture, organic matter, and yield of vegetable crops

The foregoing discussion deals with the relations between fertilizer treatment, soil moisture, organic matter, and crop yields. The data on which the discussions are based are the measurements of soil moisture percentage on certain plats at various intervals during part of the growing seasons of 1928 and 1929, the percentages of humus in the soil of these plats, the crop yields of the plats throughout the period during which they had been under experiment (12 years), and the fertilizer treatments which had been given to the plats. The following relations have been pointed out: 1. There was no apparent association between the amounts of the different commercial fertilizers and the percentages of soil moisture or of organic matter. 2. The only fertilizer treatments which had a significant influence on soil moisture and organic matter were heavy applications of barnyard manure. 3. The crop yields were correlated to a significant degree with soil moisture without regard to the different fertilizers applied. The relative soil moisture was one of the very important conditions influencing crop yields--possibly the most important. 4. The percentages of soil organic matter and moisture were correlated to a significant degree with each other and with crop yields. 5. The correlation between the yields of all crops during the period of the experiment and the average percentages of soil moisture is greater than that between the average percentages of soil moisture in a particular season and the yields of the crops grown in the same season. This indicates that the relative crop yields and the soil moisture were characteristics of the plats studied which did not change greatly in their relation to each other during the period of the experiment. 6. The topography as it affected surface drainage is suggested as one of the physical features which might have had an important influence on the moisture content of the plats. It is to be emphasized that causal relationships between the various conditions have not been pointed out in this discussion. It has not been shown, for example, whether differences in the percentage of organic matter brought about the differences in the percentage of soil moisture or whether the differences in soil moisture which were characteristic of the plats resulted in different percentages of organic matter through greater crop residues. It may safely be assumed, however, that differences in soil moisture brought about differences in crop yield. The degree of association between these two factors, as shown by the coefficient of correlation between them, indicates that the influence of natural differences in soil moisture in determining the crop yields was very great.