ONION SOILS.

Auckland Star, Volume LXVI, Issue 70, 23 March 1935, Page 6 (Supplement)

ONION SOILS.

AND THEIR MANAGEMENT. In a bulletin on "onion growing, the Ministry of Agriculture (England) says:—The soils in which heavy crops of good onions are produced are all freely supplied with water, yet well drained. They are easy to cultivate, and can be made into a firm bed with a fine tilth at the surface, and yet rem'ain free from any tendency to pack hard. In Bedfordshire the easily worked loarns that bed down well are selected as being the most suitable for onions. These soils belong to several types. In the United States the "muck" soils are generally considered the most suitable for main crop onions, which are grown in New York State, Ohio, Indiana, Michigan and California. Muck soils consist largely of plant remains that have almost completely decomposed. They are easily brought into good tilth, and have a high waterholding capacity, a feature of even greater importance in the United States, where the summer is hot ami dry. Drier soils such as sandy and silty loams and silts are also used for early crops that mature at the beginning of the-long summer drought. Alluvial silt soils, and even sands, are used for growing onions in Holland, Spain and Egypt. Light sands can be used, provided that the water table is sufficiently high for the onions to obtain the abundant supplies of water that they need, and such conditions are realised in Holland. On these soils a high Wciter-holding capacity is less essential. The alluvial soils of the onion-growing district of southern Spain are well watered by irrigation canals. Where onions are grown in the Nile valley of Egypt, the soils are rich alluvium, of which the "yellow land," a sandy silt, is regarded as the best. Alluvial and sandy soils, or a mixture of these, are well suited to onion production, provided they are well supplied with moisture. The manuring of the onion crop depends largely on climatic conditions. Bedfordshire growers have relied in the past very largely on London dung or farmyard manure, which, in addition to its fertilising action, has an important beneficial eifect on soil texture, jjreventing it from drying out in the early summer. I i many parts of Holland the requirements are different, for the necessary moisture is maintained by the very high water table, and growers are able to dispense almost entirely with farmyard manure. In parts of the United States, where farmyard manure is difficult to obtain, growers often turn in a green manurial crop before growing onions. Farmyard or stable manure, when used, must be well decomposed before the seed is sown; it is, therefore, kept for several months in a stack and then spread over the :Soil some two or three months before seeding. American growers in southwestern Texas use considerable amounts of sheep and goat manure, which is stored for several months in compost heaps so as to reach a suitable condition. This compost is applied at the rate of 20 tons per acre, supplemented by 10001b to 20001b of cotton seed waste or artificial fertiliser per acre, and sometimes a topdressing of nirate of soda fs applied. Unless the manure is sufficiently decomposed or "short," the plants are stimulated into excessive leaf growth at the expense of bulb formation, and later become coarse. , Where farmyard manure is not available generous dressings of fertilisers must be applied, for onions are gross feeders. Dutch growers rely almost entirely on artificials, and an example of the mixture applied is Bc\vt eulphate of ammonia, 2cwt sulphate of potash per acre, per annum.

As previously mentioned the high water table in Holland makes it possible to use artificials instead of organic manure. In the United States a "complete" fertiliser such as is used for potatoes is commonly applied shortly before sowing the seed in spring. Muriate of potash is preferred to sulphate of potash, the mixture containing approximately 4 per cent to 5 per cent nitrogen, 8 per cent to 10 per cent phosphoric acid, and 8 per cent to 10 per cent potash, and is applied at the rate of 10001b per acre. Thorough

experiments have been carried out on the muck soils; . these are naturally well supplied with decomposed vegetable remains, so that farmyard manure is unnecessary, and growers rely largely on chemical fertilisers. An application of a mixture such as the following is usually sufficient: —5001b superphosphate, 2001b to 4001b muriate of potash, per acre. Nitrogen is not usually required, although nitrate of soda (1001b per acre) may be applied on these soils to give the' onions a start in the spring. In England, dung has been the standard manure, and fertilisers have hardly been fully tried out. Where used in Bedfordshire, however, mixtures such as the following have given satisfactory results: —3 parts superphosphate, 2 parts sulphate of ammonia, 1 part sulphate of potash. An adequacy of nitrogen alone is not in itself sufficient for the production of good crops of satisfactory onions; potassium and phosphorus are also important. Phosphates increase yield and potash promotes early ripening, and appears to improve the keeping quality and attractiveness of the bulbs. When there is a deficiency of potash, which generally means a relative excess of nitrogen, the bulbs do not ripen well and are liable to develop neck rot. Experiments at the Horticultural Research Station, Cambridge, indicated that a dressing of 4cwt of sulphate of potash per acre, applied either in spring or in autumn, gave beneficial results. Larger quantities led to an excess of potash, causing rather premature ripening, and consequently rather smaller bulbs, which, however, kept particularly well, and were remarkably free from neck rot (botrytis rot). A plentiful supply of lime is essential. It is significant that all the samples of good "onion land" in Bedfordshire analysed, contained a large proportion of lime, while practical experience with soils containing less natural lime has indicated the very good results obtained by liming in the autumn before sowing. Growers consider that when lime is abundant the bulbs are of better quality, keep longer and are less susceptible to infection with the fungus botrytis.