SOIL FERTILITY.

Putaruru Press, Volume VIII, Issue 349, 31 July 1930, Page 6

SOIL FERTILITY.

SUPPLY OF PLANT FOOD. 1 Factor s whicu influence soil fertility.' the principal ones being tile available supply of and the physical and biological condition of tne soil, are dealt with in a pamphlet Jaiely issued by the New South Wales Department of Agriculture. The conditions necessary tor optimum plant growth are given a s follows:—(I) i'liere must be a su ciency of water; (2) There must be a sufficiency of air; (.3J There must be a sufficiency of plant-food; (4/ Tlie conditions regarding temperature | must be correct; (5) The plant, must [ have adequate root room; (0) Toxic or j poisonous substances must be absent, j Any one of these may be a 4 ‘limiting I factor” as regards fertility of soil.

The soil is not an inert mass of material, out of which the plant picks whatever material is present for its nourishment, and having regarded as the medium in which the plant grows, and in which complex changes, chemical and biological, are taking place among the constituents. When we talk of change s that take place in the soil, says the writer, we must realise that the changes are constantly going on, that the material of which the soil is composed i s continually altering, that the growth and decay of plants, the movement of earth worms and minute organisms, the fall of rain, the evaporation of moisture, alterations of temperature, of night and day, of summer and winter, even alterations \of atmospheric pressure, the passing j of clouds, and countless other pheuoI nicira of which we take no heed, or • whose action wc do not yet fully under I stand, all these agencies produce an { incessant series of changes within the J soil. When we add to these the J changes produced by human agencies— I by cultivation, by ploughing, liming, \ manuring, etc- —it will be seen at once ) that a mere statement of the amount

of fertilising material (potash, lime, phosphoric acid, and nitrogen) in the soil, even if we could say how much was actually available for any particular crop, is not all that is required to permit an evaluation of the soil’s fertility. The fertility of a soil depends, then, in the first place, upon the presence of a sufficiency of plant-food in a readily available form, and secondly, upon certain physical characteristics, possessed more or less by all soils, which affect the splitting up of the mineral ingredients and nitrogenous matter in such a way as to render them available to plants, as well as regulating the supply of water, warmth, ©to.