Effects of fertilizers on yields and breaking strengths of American hemp, Cannabis sativa

There was little information regarding the effects of fertilizers on yields and quality of hemp fiber as produced in this country prior to 1943 when the acreage was greatly expanded. Research with flax indicated that abundant nitrogen might lower the quality of that fiber. A series of fertilizer experiments with hemp was begun in Wisconsin and Illinois in 1943. The soils were in good state of fertility and responded only moderately to fertilizers. Nitrogen at 9 pounds per acre reduced the mean breaking strength of fiber by 4.4%. The experiments of 1944 included two which responded markedly to nitrogen and two which gave no response. On the former fields nitrogen did not significantly reduce breaking strength, but on the latter nitrogen at 100 pounds per acre caused a mean reduction of 14.7% in breaking strength of fiber. In experiments in Indiana increasing the application of 8-8-8 fertilizer through 0,500 and 1,000 pounds per acre increased the yield and caused general progressive reductions in breaking strength of fiber. For the 1,000-pound rate the reduction amounted to an average of a 11.1%. In an experiment on peat soil in 1943 heavy applications of mineral fertilizers produced high yields, but the fiber was of poor quality. In 1944, the level of available nitrogen was reduced by spring plowing a sod and applications of carbonaceous materials, and minerals were applied. The yield was only moderate but the fiber had good quality and breaking strength. Abundant nitrogen causes a more leafy and succulent type of growth in hemp, and tends to increase stem diameter above the optimum range. These characters were associated with lower breaking strength of fiber in these experiments. Hemp makes a rapid growth, and adequate supplies of available nitrogen are essential for satisfactory crops. However, these data indicate clearly that excessive applications should be avoided. The problem is one of adjusting rates and balances of nutrients in such a way as to assure maximum production and at the same time maintain fiber quality. From the point of view of the grower, some loss in fiber strength may be justified if the increased yields give a greater net income.