VEGETABLE SOIL

Wairarapa Times-Age, 24 March 1939, Page 9

VEGETABLE SOIL

MUST BE FERTILE.

The maintenance of the soil in a highly-productive condition with the minimum expenditure is probably the most serious problem at present confronting vegetable growers. The intensive cropping associated with vegetable gardening results in the removal of large amounts of plant food constituents and, unless care and foresight are shown by the grower, the land quickly becomes impoverished, with a corresponding reduction in its productive capacity. It is estimated that carbohydrates and water constitute between 90 and 95 per cent of the weight of most of our vegetables. The plant obtains carbon from the air by means of its leaves: and water is taken up by the roots as are all the other _ plant foo’ds that are present in solution in the water. The substances that have come to be regarded as the most important, because naturally available supplies are usually insufficient for the raising of heavy crops, are nitrogen, phosphorus, potash and calcium. These, when present in sufficient and balanced quantities, are associated with a condition of high fertility and it is the object of scientific manuring and cultural practices to make good the losses and supply deficiencies of these plant foods. The importance of humus, the decayed or decaying organic matter in the soil, cannot be over stated. It not only improves the physical condition, simplifies moisture regulation and aeration of the soil, but it furnishes the growth media for bacteria, without which many of the organic nitrogenous substances applied to the soil could never be brought into a form suitable for assimilation by the plant. Humus also supplies organic acids that perform important functions in relation to other plant foods of a mineral origin. Farmyard and stable manures have been recommended and applied to the land as fertilisers for centuries past, not only because they contain the essential plant foods, but because they supply the necessary humus as well. Soils of older settled countries have been made productive of vegetables mainly with the aid of enormous quantities of stable manure drawn from the towns and and cities ever since market gardening became a specialised industry. It was unusual for market gardeners to keep live stock for the purpose of making manure, and a feature of their business in the past was the arrangement whereby the carts and wagons that conveyed produce to the markets always returned loaded with town stable manure.

Till a few years ago this manure was always freely obtainable and the growers came to depend on these supplies, but now, owing to the development of motor transport, stable manure has become scarce and supplies are still dwindling. It has become necessary, therefore. tc> cast about for other Means of mainlaing soil fertility. Although the problem is difficult it is not of insuperable difficulty and vegetable growers should be able to maintain, even improve, the present productiveness of their land, by making use of green crops, by sound methods of cultivation, by employing a system of rotation so that the' best use is made of the land and its fertility, and by intelligent use of the wide range of modern fertilisers.

In Rhode Island, a series of experiments, designed to ascertain the extern to which stable manure could be replaced by inorganic fertilisers in combination with green manuring, was continued for a period of six years. A rotation was planned that allowed five cash crops to be taken over a period of three years. The results conclusively showed that when a green crop, such as a mixture of ryegrass and clover, was substituted for one of the crops in the rotation, and ploughed in. and a complete mixture of commercial fertilisers was substituted for half the usual amount of stable manure, it was possible to obtain better yields and a higher net cash return for the three years rotation, notwithstanding the fact that one of the five cash crops was lost. In the same experiments it was ascertained that higher net cash returns in any one year were also obtainable by substituting commercial fertilisers for half the amount of stable manure

normally employed. Similar significant results were obtained in the State of Illinois in experiments carried on for a period of five years. It was found that when greens were grown to supply humus, stable manure could 'be entirely replaced by inorganic fertilisers without detriment to the crop yield.