USE OF FERTILISERS

New Zealand Herald, Volume LXXII, Issue 22005, 11 January 1935, Page 16

USE OF FERTILISERS

PROFITABLE APPLICATIONS VALUE FOR TOP-DRESSING REPLACING PLANT FOODS Fertilisers have definitely proved their value for top-dressing pastures. The only practical considerations now are at what times, and in what quantities, they should bo applied, and what artificial manures, or combination of them, is most likely to give the best results under the climatic and soil conditions generally prevailing. Broadly, it can be said that New Zealand soils require lime, phosphate,' nitrogen and potash. In some particularly light soils the bulk of these could be supplied most effectively in the form of blood and hone, but on the score of expenso many formers nowadays prefer to rely on the commercial forms of lime, superphosphate, sulphate of ammonia and potash salts. Limo and phosphates are discovered to be the elements most generally deficient in the surface soil, where they are available only to tho shallowrooted grass plants. Thus soils which may contain these in considerable quantity in tho subsoil, may be very deficient in available supplies. Some volcanic soils aro particularly deficient in lime, while in other localities, and prncipally where land has once been sea-bed and is largely composed of lime deposits, the actual surface soil may bo lime-deficient as a result of leaching.

Deficiencies ol Lime Because it is readily soluble in cold water, lime is more likely to bo deficient in a wet than in a normally dry climate. A rather interesting provision of Nature, to counteract the removal of lime from the surface soil by leaching, is seen in the fact that cold water will hold in solution a groatei quantity of lime than when it is warmed. Thus cold, heavily-impreg-nated springs bring lime to the surface where, as the water is warmed by the sun, considerable quantities of lime are deposited, sometimes forming deltas and terraces tending to a still greater deposit and wider distribution of lime over the surface. This natural action, however, cannot be solely relied upon to replace tho largo quantity of calcium removed from the surface soil by leaching and by depasturing stock, and in many districts, especially where the soil is of a heavy or clayey nature, or where the rainfall is high, regular and heavy dressings of lime are essential.

In drier districts, and particularly where the soil is of a sandy or very light nature, and is deficient m humus, a heavy application of limo may do more harm than good. Through verv much the same agencies, the original supply of phosphates has been depleted from the surface soils which, in tho North Island at any rate, were never in over-supply, and in nearly every district the land will respond handsomely to top-dressing with superphosphate.

Importance of Potash

Potash salts, although giving marked results in some districts—notably Taranaki—have, in tho main, not rewarded the farmer with the obvious results that would be expected from a soil or pasture analysis. It is certain, however, from its importance in stimulating plant growth and nutritive value, that the application ot potash should not bo overlooked nor discontinued until it is conclusively proved that it is conferring no protitablo addition to tho available plant food.

Applications of nitrogen in the form of sulphate of ammonia or nitrate of soda appear to give greatest beneficial results in climates or seasons of deficient sunshine, for as it stimulates leaf growth, the plant is through them able to absorb a greater amount of nutriment from whatever sunshine is available. It is of particular use, therefore, for stimulating leaf growth in autumn, winter and early spring, when, as a result, tlio grass plants will make more growth of better quality fodder.

A Profitable Programme

As a guide for general use, *it is safe to say that tho dairy farmer who regularly applies 2Jcwt. of carbonate of lime to his grassland every year, or double this quantity every second year, and supplements this with a dressing of 2Jcwt. of superphosphate and Acwt. of potash a year, will always make a profit on the outlay. Regulation of the amounts of each ingredient and the beneficial effect of additions of nitrogen can only, be discovered by tests under pr.ictical conditions in each district.

As grass growth is usually ample in spring and early summer, top-dressing to overcomo tho shortages occurring in winter and certain periods of summer and autumn should be concentrated upon. Just as tho early practice of heavily top-dressing once in every two o]* three years has now given place to annual lighter dressings, so tho principle can be advantageously extended to top-dressing at various seasons of the year to secure extra growth and nourishment when it will bo of greatest value on the farm.

Seasons ol Shortage

On most dairy farms the feed requirements are more pressing in JulyAugust, January-February and MayJune. To provide for extra growth in thoso seasons, the application of fertiliser must bo made at from a month to six weeks prior to the growth being required, and in the dormant season — July-August —at least two months previously. Using the grass while it is in its growing stage shortly after tho application of fertilisers will mean that it is used when in the stage of its greatest nutritional value, and the maximum return will therefore bo secured from the outlay. Dressings in excess of what can bo promptly utilised by the existing sward cannot bo looked upon as economic outlay, and only careful experiment, with records of applications and results, will safely guide the farmer to tho maximum amount ho can -apply with the greatest immediate profit.