A Study of the Validity of Laboratory Techniques in Appraising the Available Nitrogen Producing Capacity of Soils

Abstract

There is urgent need for a laboratory procedure capable of determining the status of the soil nitrogen, one which will predict the ability of a given soil to quickly replenish nitrates removed by cropping and leaching. Such a method would be useful in evaluating soil management systems and in determining the need for nitrogenous fertilizers. A laboratory method is described involving incubation under controlled conditions for 12 weeks with bi‐weekly removal of nitrates produced. This method was found to be successful but time‐consuming. Distillation of ammonia from soils in the presence of alkaline permanganate gave recoveries which were well correlated with incubation results. Both procedures showed that from 200 to 400 pounds out of the 2,000 to 4,000 pounds of total nitrogen in soils are biologically active. With these methods it was possible to show that long continued use of manure leads to a backlog of biologically active nitrogen. Acidity likewise favors accumulation while excessive liming without proper provisions for maintenance depletes the active organic nitrogen supply. Prolonged acidity causes a decline in microbiological activity, permitting potentially active forms of organic nitrogen to accumulate. When this acidity is corrected, as in the laboratory procedure described or as in tier II of the Jordan plots, the yields are higher than on the corresponding less acid plots. It is suggested that either method is quite useful in evaluating soils and soil management systems, but of questionable value in determining the nitrogen fertilizer requirements for the current year. Nitrate delivery to a given crop depends, not only upon the presence of easily ammonifiable organic nitrogen in the soil, but also upon the soil conditions prevailing at the moment. The available nitrogen requirement of a given crop depends upon the adequacy of other growth factors. A very poor correlation was obtained in the field between response to nitrogen and the quantity of easily nitrifiable organic nitrogen in those soils.

Comparison of Nitrate Production and Other Procedures in Determining Nitrogen Availability in Southeastern Coastal Plain Soils1

“…The idea has been postulated that certain fractions of organic matter are more readily decomposed than other fractions (11,21). Although a considerable amount of work is being done on the chemistry of soil organic matter, no fraction yet has been identified as the so-called available N fraction.…”

Relationship Between NO3‐N Production, Dry‐Matter Production and N Responses on Coastal Plain Soils1

“…T HE conversion of soil N from organic to available forms during the growing period of a crop can be an important factor affecting yield responses from applied N. Much effort has been expended during recent years to refine the methods used for estimating the availability of soil N (1,2,4,6,9,10,11,12). This work has centered around soil tests for N.…”

Modification of the Alkaline Permanganate Method for Assessing the Availability of Soil Nitrogen in Upland Soils

“…The alkaline permanganate digestion method has been widely used for assessing the available nitrogen pool in soils, especially in India (Truog 1954; Subbiah and Asija 1956; Kresage and Mer kle 1957; Tamhane and Subbiah 1962; Bajaj et al 1967;Stanford and Legg 1968;Singh and Tripathi 1970;Ranganathan et al 1972). This method was originally developed for estimating the easily oxidizable organic nitrogen fraction in organic manures and fertilizer (AOAC 1930); its adoption for soil studies followed the demonstra tion of fair correlations between the amounts of nitrogen extracted by this technique and the mineralizable nitrogen contents of soils (Subbiah and Asija 1956; Boswell et al 1962; Kresge and Merkle 1957;Herlihy 1972;Stanford 1978; Sah rawat 1978) and nitrogen uptake and yield of different crops, including rice (Munson and Stanford 1955; Kresge and Merkle 1957;Bajaj et al 1967;Stanford and Legg 1968;Rajamannar et al 1970;Ranganathan et al 1972;Sahrawat 1978). Other studies have indicated that the method gives good correlation with the response of rice to applied fertilizer nitrogen (Bajaj et al 1967; Rajamannar et al 1970;Sahrawat 1978).…”