SOIL FERTILITY

Hokitika Guardian, 18 August 1928, Page 1

SOIL FERTILITY

CAUSE AND CONTROL ! the value of phosphates. CHRISTCHURCH, Aug. 10. Sir John Russell, Director ol" the Rothamstcd Experimental Station. England, delivered a lecture on “Soil Fertility—lts Cause' and Control,” to a, large attendance in the Canterbury College Hall last evening. The Hon. Mr Smith (chairman of the Board of Governors) presided. Sir John Russell, in opening liis address, said that agricultural investigators had spent a great deal of time studying fertile soils and infertile soils. By fertilo soil he meant soil on which plants would grow well, and for that there were six requirements. In the first place it must lie deep enough tor the plant roots to move about in. If it were wet it would have to he drained, or if there were a. pan underneath that would have to he broken. Then the plant lmd to be furnished with enough wafer. It took anything from 3001 b to 9001 b of water, to produce one pound of dried crop. Further,: the roots required air. and unless the soil enabled the air to penetrate to the roots it could not bo fertile. This was one, way in which plants sulferod more than in anything else. Again, plants required food, and lastly, they should be warm enough. That was a matter which depended partly on the soil, hut, mainly on the degree ol wetness. In modern times, lie went on, the art of cultivation was not practised as much as it might ho. Labour, for one thing, was not very expert. Unless cultivation were done well soil, could not lie made any more fertile by putting more Tood into it. Cultivation was the main necessity. It regulated the water supply and ensured a supply of air to the roots, and that the land was in a good condition in which plant foods could grow. Finally, it kept down weeds. THREE MATX GROUPS.

“Weeds will do in a very short time more harm to a crop than any amount of starvation will,” said Sir Joint. “They take up food which the plant, requires, and water, which the plant ought to liavo, and they seem to have some effect on the plants themselves. Once cultivation is done well you can begin to use fertilisers with effect.” Fertilisers, he explained, were divided into three main groups—the nitrogenous, the iplTosphatro, .and the potassic organic. The organic group whs the- oldest known fertilisers, and reference to some of them was found in the oldest agriculturalists literature. The older agriculturalists know a great deal more about blood as a manure than we knew to-day. These organic manures were in the main fool-proof, and were very useful indeed ill the gardens. But they were not the best for farmers because they wore more expensive and not so quick in acting as the artificial fortilisois, which, however, required some understanding of their correct use. “At Rothamsted,” the speaker went on, “wo have five or six fields that have received superphosphate for 70 vears, and we can fc find the smallest evidence that it has made the soil acid. We have tried the experiment on soil of a different type where it had been applied every year for GO years, and here again there is no sign that it has made the soil acid. We know just how much superphosphate we have added, aind we know how much crop wo have taken off, and we make a sort of balance sheet. The amount of superphosphate that is put in the ground is all there after you take into consideration all that lias been used by the plant. That is to say, there is no waste. One of the effects of superphosphate is to increase the growth of the root (a point which was demonstrated by slides showing the growth of swedes). Nitrogenous fertilisers on the other band induce larger leaf growth. When you have satisfied tlio requirements of tbe plant for tbe thing it needs most, then you can give it the nitrogenous fertiliser.”

FOOD FOR ANIMALS. Another well-known effect of phosphates was the improving of food crops for animals. Tu his experience they did not, however, get as good results in mineral phosphate as in tbe other phosphates, such as basic slag. But where there were not sufficient stock on the grass it grew too quickly and became fibrous, so that the animals did not like it, and did not do well. It

was, therefore, necessary to keep sufficient animals to control the growth. The most nutritious herbage for animals was the young herbage, and consequently the grazing should be so arranged that the grass was always eaten down. In the intensive manuring of grass lands that principle formed the basis of their experiments, the paddocks being divided up Into small areas and the manure put on in turn, the animals being then worked through them one by one. They were rotated over the ground three or four times during a season. By applying this method of manuring farmers were enabled to extend their grazing perior by some six weeks.

Another manure was potassic manure. Tt was always a matter of experiment which crops should receive the potash. At Rothamsted they gave it, as a rule to the sugar plants, such as beet, as it was found that an acre of ground produced much more sugar where potash was used. The quality also improved. That, however, was still a subject of experimentation, as it might he that thero was already potash in the, soil. LIGHT SOILS. “There is no better way of managing light soils than by growing green crops and letting the sheep run on them,” Sir John stated, “for they constitute one of the best ways of maintaining the fertility of light soils. One of tlie best ways of maintining tlio supply of organic matter in the soil is to grow the crops in rotationswedes, barley, clover, and wheat were the old Norfolk order. The swedes aro fed off to the sheep and the clover residue is ploughed in and that keeps up the supply of organic matter. Green manuring is excellent if the crop is ploughed in while it is .still green. It is useful enough when the rainfall is sufficiently high, hut I have not seen it successful where tlio rainfall is less than 20 inches. The rotting down of straw, with properly fed organisms also provided a very valuables manure. The soil must not, only receive organic matter, hut also limestone, for plants would not tolerate an acid or sour soil. A good many soils were sour and the introduction of limestone to them was necessary. Fortunately chemists were able to measure the acidity of the soil and advise flic farmer how much calcium carbonate to put in to make it neutral.

“Tn spite of years of work on soil fertility thero still remains a great deal that we do not understand, and wo can only keep on experimenting,” Sir John cone hi del amid applause. Mr John Deans moved a hearty vote of thanks to Sir John for his lecture. Mr M. E. Lyons seconded the motion.