Farm and Garden

King Country Chronicle, Volume IV, Issue 223, 8 January 1910, Page 3

Farm and Garden

TO THE NEEDS OF A SOIL.

"Mark Lane Express." To ascertain the needs of a soil for plant food is not a simple matter. Chemical analysis, while it supplies useful information, is not a certain guide, especially with regard to soils that have, been under cultivation for some time. For example, as Mr Fraps, of Texas Experimental Station, pointed out in a recent lecture, the rice soils of Texas contain from 5001b to 8001b of phosphoric acid per acre in the surafce foot, but the application of 281b phosphoric acid in superphosphate has a great effect upon the yield. There is plenty of phosphoric acid in the soil, but not, sufficient of it is in such forms that plants can take it.up, hence the decided effect of the addition of a comparatively small quantity of phosphoric acid that plants can take it up. Ordinarily chemical analysis shows the amount of plant food in the soil, but it does not distinguish between that which the plant can take up and which it cannot. Hence while this chemical analysis shows the possibilities of a soil under good treatment, it does not show the immediate needs of the soil. Another method of ascertaining the need of a soil for plant food is by means of field tests. A field is selected uniform in all respects, and it is divided into plots, say one-tenth acre each in size. These plots are treated alike in all respects, excepting that they receive different fertilisers. The yield of the crop planted is taken as a measure of the effect of the various applications. Plot experiments are subjected to vicissitudes of the weather, the depredations of insects, and other variable conditions. A soil which appears uniform may really be variable in depth or chemical composition. Heat and cold, moisture and drought, affect the crop, and the controlling influence in the development of the plant may be, at various periods during the season, other than the plant food in the soil. For these reasons the results of plot experiments are ofter irregular, contradictory and unsatisfactory. Yet, if carried on for a sufficient number of years, land when properly planned and conducted, plot experiments give results which can be secured by no other means of experimentation, and the ultimate test of laboratory conclu • sions must be in the field. Plot experiments are • expensive, require considerable time, and the results are applicable only to the kind of soil under experiment. The results of such experiments should be correlated with the various types of soil before general application is made of the results. Another method of ascertaining the need of the soil is by pot experiments. In these experiments the soil is mixed thoroughly, and portions of 101b or more placed in pots, and plants grown therein. For example, if we desire to ascertain whether or not a given soil is deficient in phosphoric acid, we would compare the crop produced by complete plant food with the crop made in the same soil without phosphoric acid. The difference between the two shows the effects of the phosphoric acid. A pot experiment can be arranged so that the soil and plant food are controlling factors in the growth of the plant. The results are secured comparatively quickly. For certain problems it is unequalled. How far the results of pot,experiments can be applied to the field is an open question. In the field the plant has a larger quantity of soil to draw from; soils may appear more deficient in pots than they do in the field. Further, the depth of the soil is a factor. That the same soil 6in deep in one place and 12in deep in another affords different amounts of plant food is too obvious for discussion. . In some cases the subsoils may supply plant food, while others do not. It is merely intended to indicate the complexities of the problem which confronts us, and yet, after all, while an analysis of the soil is interesting, especially from a scientific point of view, is it essential that a farmer, dealing with old cultivated lands, should be acquainted with the exact constituents of the soil of his fields? May it not be sufficient for him to know that all soils, unless farmyard manure is applied in large quantities, require applications of phosphate of lime in an available form, that all crops apart from the leguminose are the better for dressings of nitrogen, and that it is advisable to try the effect of potash, especially for potashloving crops, such as potatoes and clover. The farmer knows at the must avoid the application of illbalanced fertilisers, and he can learn much by a few simple experiment i on his) own farm and by'comparing notes with other farmers in the locality.