Composition of soil as affected by different cropping systems
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Among the experiments in soil fertility which are being carried out by the University of Missouri College of Agriculture is a series of plot experiments which have been in progress since 1889. There are thirty-nine plots in the field and each has received a definite treatment during this time, the aim being to compare the effect of rotations with continuous single crops, both with and without fertilizer, and to compare the effect of commercial fertilizers with that of barnyard manure. Some striking differences in yields have been obtained but no effort had been made to investigate the changes produced in the composition of the soil until 1909, when Dr. L.D. Haigh took samples from a series of the plots and determined the hygroscopic moisture, total nitrogen and acidity. The humus, total phosphoric acid and the phosphoric acid soluble in N/5 HC1, total potassium, calcium, magnesium and the lime requirement by the Veitch method have since been determined on these samples and these data, as well as the determinations made by Dr. Haigh, are presented in the following thesis. For the present study, eleven plots from the experimental field and the uncultivated soil were selected. The plots are one thirteenth of an acre in size and each has been receiving the given treatment for twenty-one years previous to the time the samples were taken. One plot has been continuously in wheat and has received chemical fertilizers. On four others, two systems of rotation have been carried out with and without manure. On the remaining six, single crops - corn, oats and timothy - have been grown with and without manure.