MALNUTRITION OF PLANTS.

Otago Witness, Issue 3383, 15 January 1919, Page 8

MALNUTRITION OF PLANTS.

Malnutrition, or the imperfect nourishment, of plants may arise either from an insufficiency of plant foods in the soil or from an excess of some particular food constituent. Just as doctors 'will maintain that people, as a rule, eat too much, especially too much nitrogenous food in the shape of meat, and from this cause become so much more liable to euch complaints as gout, skin diseases, etc., so do plant experts assure us that in the continuous growing of closely-related crops by the use of too much forcing manures, particularly those of a nitrogenous nature, there is a danger that plants will suffer if not actual disease, then assuredly there will be a diminution in the quality of the crop. Thus turnips may develop, undue tops and lack quality, and be of too watery a nature, potatoes may become unsightly from spotty skins, cereals get their tender stems easily attacked by insects. Plants grown in greenhouses and in market gardens, where intensive cultivation is the rule, are especially liable to suffer from an excess of nourishment of too nitrogenous a nature, or a supply of ill-balanced plant foods. Oops are grown in quick succession year after year on the same soil, continually enriched by large dressings of stable manure and fertilisers, so that the soil becomes quite surfeited with plant food, and does not get the healthy influence of a period of fallow or the cliance of a radical change of crops. An expert of an American Agricultural Experimental Station devoted for some years special study to this subject in consequence of the attention of the station having been called to an increasing number of plant troubles, and in a good number of cases he found typical cases of malnutrition, caused by an excess of some particular substance in the soil. These troubles, according to his investigation, "all originate from an injudicious use of commercial fertilisers, or from applying certain manures to crops in excess of what they can stand." In some cases, as no doubt some of our readers- have experienced, an excess of fertilisers causes burning of the roots, which results in the death of the plant; but usually the greater trouble comes from an excess of nitrates in. the soil—that is, in the case of intensive cultivation under common enough market conditions. In several instances of tomato plant disease it was found that they had been affected by the excessive use of fertilisers, and tests of the foliage for nitrates revealed an excess in the leaves. They had a curled and crinkled appearance, caused by the contorted vascular bundles or veins. These symptoms have been occasionally found in the field as well as in plants growing in greenhouses, and. analyses nave shown the nitrate excess. Some of the most severe cases of malnutrition resulted from the use oT fowl manure worked into soil already provided with an abundance of plant food, such as would be obtained from a constant use of horse manure! In numerous cases where fowl manure was freely used symptoms of malnutrition followed. An experi-. ment was made in one of the houses of the station, devoted exclusively to the growing of American Beauty roses. The soil was prepared,* as usual, with a rich dressing of stable and cow manure, and liquid manure was applied freelv once a week. The first year the roses did well, and for the purpose of experiment an attempt was made to grow a new crop of roses on the same soil, which was partially renewed by application of liquid cow manure. The plants had not been in the soil many weeks before they began to die, and it was not unusual for many to die in one week. The result of this experiment was only what was expected; the beds were then flooded with water, and analyses made of the water that drained through the soil. The result was surprising, and it was difficult to conceive of any plant living under such soil conditions. After the soil had been drenched and the injurious substances washed out, not a death occurred among the plants. From the nature of the conditions causing malnutrition a remedy is not difficult to find. The first essential is, of course, to be careful in the use of manures and fertilisers. The excessive use of nitrogenous fertilisers, unless balanced by other constituents, especiallv of lime, is to be avoided. The soil must be kept open, well drained, and aerated. The change of crops by suitable rotation is always advisable." In the treatment of beds and small surfaces it has been found very beneficial to cover the soil with a few inches of loam—new roots quickly form in the loam, and have supplied the plant with proper food for its right development.