THE VALUE OF SOIL ANALYSIS TO THE FARMER.

Otago Witness, Issue 3100, 13 August 1913, Page 14

THE VALUE OF SOIL ANALYSIS TO THE FARMER.

The various agencies which have been at work in farming on soils for ages past need not concern us at present, except to state that all soils are mainly composed in varying proportions of sand, clay, chalk, and humus, and the ideal soil is a judicous

blend of these. They are all necessary in a fertile soil, bat, perhaps, chalk, or lime, is the chief basis of fertility in any soil. It is not merely compounds containing lime, like bones, superphosphate, or slag, that are necessary, but quicklime, or carbonate of lime, that will provide a base to neutralise the acids that are always arising from the decay of vegetable' matter. Methods of analysis which will measure a very small amount of lime are possessed by the analyst. Despite many years of continuous work and experiment, scientific men have not yet

completely solved tlio problem of the fertility of the soil, but in recent years vast strides have been made, mainly in the direction of regarding the soil as a “living” mass instead of dead, inert natter. The analyst was confronted with the fact that there was little difference in composition between one cfop and .mother, between a healthy and diseased one -All plants contain the same range of elements drawn from the soil and in very nuch tne same proportions. The amount they extract from the soil is only a fraction of what exists there, yet the addition of a small quantity of one ingredient may increase the crop 20 per ,cent. .Many attempts were made to obtain a precise distinction between the available and the dormant plant-food, but without any great measure of success. Judging from analogy the analyst can advise the farmer.. He can tell whether the land gives an alkaline or acid reaction, whether to lime It or not, whether to use nitrate of soda or sulphate of ammonia, when he wants a quick-acting fertiliser, whether for his turnips superphosphate or basic slag should be chosen, or some neutral body like phosphatic guano or steamed bone flour. But other resources are available to the scientific adviser, and Mr A. H. Hall describes them in the Royal Society’s Journal. He shows that a mechanical analysis of the soil gives precision, and reduces to definite figures the farmer's way of considering his soil. The farmer defines his land as heavy or light—a loam, a sandy clay, etc; the mechanical analysis reduces the relative proportions of sand and clay to figures which are independent of the personal equation and of climate, and which so greatly affects the impression a soil gives. It gives at once a good deal of information as to its behaviour under cultivation, but takes the investigator very little nearer the answers to the question why a given soil does not answer for a particular crop, and how it can be ameliorated. The mechanical examination, however, brings the analyst closer to the farmer’s demands. Soils and their behaviour can be grouped more effectively by the mechanical condition than by their chemical composition, it was found that all fruit soils, for instance, fell within the limits of a faii-ly well defined type; the potato soils, again, constituted another somewhat different type, as also did the barley soils. The adaptability of- a soil to a particular crop was therefore determined in the first place by its physical structure as revealed by the process of mechanical analysis. Further, by correlating from a large number of cases, and recording the crops known to answer them, a specification, as it were, of a wheat soil or a barley soil, a soil suitable for any crop might bo worked out which would in the main be simply a generalisation from actual experience on the ground. It could thus be determined whether or not a particular crop could be extended into a new district. The soil analyst could tell to what extent the soil agreed with the soils on which the. crop had been successfully grown, and between them a warning might be given of an unprofitable venture. Although highly useful, the mechanical condition of the soil is only one more factor in a very complex and obscure result. We have also to take into account the rainfall, situation, and other climatic considerations. Another line of attack has recently been attempted. The soil can he put under standard conditions of moisture and warmth in tire laboratory, and the rate determined at which ” it undergoes chemical change by reason of the bacteria, it contains.' This method discriminates between fertile and poor soils, but does not yet throw any light on the causes of the differences in the crop stated, and has to be applied to a large number of known soils before their value in forming an opinion can be assessed. Air Hall summarises tne present position of soil analysis as follows: (1) Mechanical analysis enables us to classify soils and assign an unknown example to its type; (2) from the type, combined with knowledge of the situation and climate, we may predict its suitability or otherwise for”particular crops; (3) chemical analysis will tell ns whether a soil is getting acid or needs liming to make it work properly and utilise the manure supplied to it; (4) from chemical analysis we can settle what class of manures ought to be used—whether sulphate of ammonia or nitrate of soda, superphosphate or basic slag; (5) chemical analysis will often reveal deficiencies and”the specific for phosphates or potash, but to do this with any certainty the composition and behaviour of soils of that type should be known from a previous coil survey.