FERTILISERS ON ACID SOILS

Sun (Auckland), Volume IV, Issue 962, 3 May 1930, Page 31

FERTILISERS ON ACID SOILS

SOME OLD IDEAS REFUTED OPNIONS OF NOTED SCIENTISTS (BY K.P.). “The average lime requirement of soils in the Auckland Province is between five and six tons of limestone an acre; the swamp soils are much more acid, showing from eight to 27 torts limestone requirement an acre.” In the course of a report to Ixis principals, the soil analyst at Messns. Kempthorne, Prosser and Company’s Westfield Works, makes the statement quoted above and it is right that the information should be made* public. It should also be explained that the above statement is made only after some years of experience ir analysing soils from all over the North Island, during which time many hundreds of analyses have been put through. Having made the announcement that most of the soil is definitely in need of lime, it now becomes necessary to indicate the best course for farmers to adopt in correcting the position. In the first place a sour soil cannot reach 100 per cent, efficiency until such time as the sourness is removed. Bacteria, tipon which so much depends in building up fertility, will not operate under acid conditions; plant foods remain more or less unavailable and artificial manures give but a poor response. Once the sourness has been overcome by the addition of lime, a wonderful series of changes take place. The harmful acid is ab sorbed and at once bacterial activity is stimulated; the soil temperature is raised substantially, and plant foods are liberated freely. Lime alone i 3 capable of changing an inert soil into one teeming with life and with ability to produce—and yet lime is not looked upon as a fertiliser. FERTILISERS THAT CORRECT ACIDITY Those farmers who have never used lime and who know that their land requires it, generally endeavour to apply fertilisers that will have the effect of correcting the acidity in the soil, but unfortunately they do not always succeed in their efforts. There is an old saying to the effect that “if you once give a dog a bad name it will stick to him.” That se'ems to be the case with superphosphate on sour laud —it is a common occurrence to hear farmers explain that it would be unwise to use super

on their land as it would only add to the acidity. No one can explain why this is so, but each one that mentions the matter has either heard or read of it somewhere, sometime, and has meekly accepted it as a statement of fact. The position is that there is not an authority today who is prepared to make such a statement over his own name, but there are several in different parts of the world who say just the opposite. SHORTSIGHTED ADVICE Much of the misconception existing among farmers is due to one of two causes:— 1. Short-sighted advice on the part of agricultural experts, or 2. Trade propaganda that tells only half the story. A recent edition of an Hast Coast daily contains an interview with an agricultural instructor, who spoke on the subject of fertilisers as follows: “Of phosphatic fertilisers, superphosphate should be given to the drier soils, while to the wetter lands, basic super, basic slag, etc., should be more beneficial.” Reading this recommendation one would be justified in thinking that there is no need to do other than use basic-super or slag on wet country to get quite good results, whereas such an assumption is absurd. "Why does such an official not go r%ht to the core of the problem by stinting that wet land should be drained and limed before it can retspond satisfactorily to fertilisers. The small amount of lime contained in basic super or basic slag would hawe to be “magic” indeed if it is to offsiet conditions such as one finds on wet undrained land. JUST AN IDEA Thltre is really no evidence available to show that a fertiliser such as basic slag has the power to correct conditions of sourness in the soil. “BasSc slag continues to be our best manure” is a statement credited to an important Agricultural Department official who. at the moment, was referring: to Taranaki conditions. Why? one asks in reply—upon what grounds is such a statement based? The answer is the usual indefinite one that Taranaki soils seem to need lime and basic slag supplies it. Does basic slilß supply it? Here is a statement by Professor Gilchrist: “The acidity of the soil on Plot 4 is quite appreciably greater than on the untretated plot in spite of the fact that it lfcas received during the 24 years the lexperiment has been in progress, a twtal dressing of about two tons of basic slag to the acre. It seems fair to conclude from this evidence that the continual application of iieavy dressings of basic slag does not suffice to supply the lime requirement of soiis under grass. On the contrary tlae results indicate that such soils am liable to become even more sour tlaan similar soils left an treated.” When we take into consideration the fact that the average New Zealand soil shows a lime requirement of three to four tons of limestone an acre, or, say, one and a-half to two tons of actual Bme, it must be realised that it is impossible: to correct this by the application of a fertiliser supplying approximately SOlb to 1601 b of lime an acre per annum. WHAT AJBOUT SUPER The claim that isuperphosphate actually corrects acidity instead of adding to it is very well supported by worldfamous authorities. Here are the statements of a £ew: Professor Connor, United States Department of Souls and Crops: “Far from increasing tie acidity of a soil to which it is applied, superphosphate assists in correcting the fault, more especially in cases where the acidity is of a mineral nature. It is. too, often assumed that soil acidity arises from the use of fertilisers in the manufacture of which sulphuric acid is used. Investigations prove that such is not the caae, but on the contrary, superphosphate, that is to si\ phosphate rendered soluble by dissolving in sulphuric acid, is an effective corrective for -certain forms of soil acidity.” Professor Dr. Kjappen (highest authority in Germany.): “We assert of superphosphate tlaut it is practically incapable of causing soil acidity, and that further it is even adapted to act under certain ci'-ciwmstances as an antidote to the most clangerous form of soil acidity, i.e., interchange acidity. Superphosphate, therefore belongs, I notwithstanding its inherently acid j composition, in no sense to the group j of physiologically acid fertilisers, but j must be regarded according to the