LIME AND POTASH

Wanganui Chronicle, Volume 74, Issue 192, 15 August 1931, Page 20 (Supplement)

LIME AND POTASH

QUESTION OF AVAILABILITY. It has long been accepted that one of

the benefits from the application of lime to the medium and heavier types of soil is its effect in liberating potash in a form available to the plant from the complex compounds known as zeolites, which compose the clay fraction of the soil. According to information in overseas agricultural papers, it now appears that the truth of this theory is seriously challenged. American research workers at the University of Tennessee Agricultural Experiment (Station, after investigations lasting over a period of 15 years, have not only been unable to substantiate the theory, but have actually proved to their own satisfaction that the opposite is the case, i.e., the addition of lime or magnesia in any of the usual forms has a depressing effect on the liberation of available potash from the soil reserves. A large number of different forms of lime and magnesia were used in the experiment at rates of dressing varying over a wide range, and the authors claim that in every case except one a similar depression in the solubility of the soil potash was noticed. The single exception was an instance where an enormous dressing equivalent to approximately 100 tons of quicklime per acre was used, in which case some liberation of potash from the soil was shown, but this, of course, has no bearing on practice. The important fact is that all the normal dressings of the various liming materials brought about a reduction in the amount of soluble potash in the soil solution of the soils studied. As further support to their contention, the authors cite cases where the excessive use of lime has brought about symptoms of potash deficiency in certain crops. It is also interesting to note that further confirmation is forthcoming from another source Investigations on certain infertile soils in Northern Illinois have shown that their unproduc tiveness is duo to a lack of available potash in conjunction with a high concentration of nitrates. This deficiency in available potash is said to be due. not to any lack of total potash in these , soils, but to their alkaline condition, which prevents it coming into solution. It is clear, therefore, that, should the conclusions of these workers become generally accepted in the future, a drastic revision of ideas on the relations of lime and potash in the soil will be necessarv.