Discussion and Summary
Growers of vegetable crops on several of the older cultivated mucks of Ohio have complained for some time of the continually decreasing yields of their crops in spite of good cultural practices over a period of as long as 60 years. The muck in some of these areas was found to be 4 feet or more deep, well drained, and in a high state of fertility as measured by quick soil tests. Their cultural practices included irrigation, ample fertilizer applications, and, as far as an experienced eye was concerned, quite adequate to secure large yields. Small areas of one of these mucks was treated with varying amounts of different fertilizers, minor element mixtures, and other specially selected soil supplements. None of the treatments produced very large crop yield increases as compared with the untreated plots during a two-year period. These data, together with the quick soil tests, tended to show that no soil nutrient deficiencies existed.
The results so far obtained led to the belief that possibly some soil condition as yet unknown, such as fauna or flora in the soil antagonistic to crop roots where no rotation was practiced, might be responsible for the lowering yields.
Large increases in celery yields were secured through the sterilization of the muck soil and, therefore, seemed to substantiate this belief.
In seeking a practical solution to the problem of decreasing crop yields over a period of years where little or no rotation is practiced, a two-year rotation of vegetables and soybeans was tried with good results. A high level of nitrates was maintained in the muck by supplemented side dressing and it is questionable, therefore, whether the beneficial effect of the soybean green manure crop could be attributed to the nitrogen residue left in the muck following the crop of soybeans.
The investigations here reported are by no means complete and are to be expanded to determine more definitely the causes and effects here briefly outlined.