Soil organic matter and manurial treatments
1927
White, J.W.
From a brief review of the literature concerning the relation of manurial treatments to the maintenance of soil organic matter, it may be concluded that the evident differences of opinion among investigators is due to variations in methods and conditions of experimentation. Where lime in its several forms has been used in connection with manure or a balanced mineral fertilizer, the temporary decrease in organic matter as the result of stimulated bacterial action is compensated by increased crop residues. There is no measureable difference in the action of caustic lime and neutral carbonate on soil organic matter when applied in their equivalent neutralizing values. Liberal use of mineral nitrogen as measured by long-time field experiments has stimulated the decay of organic matter in excess of such action by mineral fertilizer without nitrogen. The laboratory observations of Sievers and Holtz concerning the effect of nitrogen on the conservation of organic matter is therefore not substantiated by long-time field experiments. The economic importance of acid phosphate and potash used in connection with a grain rotation is emphasized by the fact that for 40 years without the use of applied nitrogen this treatment has maintained crop yields and soil organic matter. (Pennsylvania field plat experiments.) The value of PK treatment in influencing the fixation of atmospheric nitrogen is shown from the fact that a total of 1,616 pounds of nitrogen have been removed by cropping on the Pennsylvania plats in 40 years and still the soil thus treated contains more residual nitrogen and organic matter than the plats treated with nitrate of soda or sulfate of ammonia.
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