Maintaining Soil Fertility

New Zealand Journal of Agriculture, Volume 62, Issue 3, 15 March 1941, Page 201

Maintaining Soil Fertility

IN the highly specialised cropping of gardens any reduction in the supply of fertilisers in addition to a shortage of organic manures creates a position which requires careful attention, more especially as regards the supply of potash, which soon becomes seriously depleted with the total removal of crops over a long period. Potash is a necessity for cropping light, sandy or peaty coastal soils, and the supply under present conditions is best obtained as far as possible in the form of seaweed. In a wet state carted seaweed contains about 1 per cent, potash, but when dry the percentage rises to 5 per cent, to 10 cent., according to the kind of weed. In a general way, seaweed is comparable with farm manure, although it is rather poorer in nitrogen, much richer in potash, poorer in

phosphates, and has a high proportion of common salt. Collected in the autumn and composted with farm manure and other organic material, it will decay, and, after turning and mixing, be in good condition for application to the land in spring at a rate of about 10 tons to the acre (5 lb. per square yard). Where large quantities of seaweed are available, it can be applied to the land in autumn as soon as it is vacant in liberal quantities of 20 tons or more per acre and turned under. Dried and sheltered from the rain, it will keep without deterioration, and be available for application later in the season in concentrated form. When cropping land at a distance from the coast the labour and cost of cartage heavily discounts the value of a bulky manure such as seaweed. Apart from what animal manures may be.

available, green cover crops have chiefly to be relied upon, and the potash requirement may be supplemented with wood ash. Root crops, legumes, and fruiting plants generally have a partiality for potash, and where high feeding with nitrogen is to be done it will be most successful when balanced off with that mineral. Wood ashes from ordinary hedge clippings contain about 11 per cent, potash, common broom 33 per cent., gorse 28 per cent., and ordinary sawmill wood ash 5.88 per cent, potassium —real potash. Half a ton (10 cwt.) of sawmill wood ash will contain potash equal in quantity to that in 1 cwt. of sulphate of potash. It will also contain those “minor elements,” the lack of which is causing serious losses in crops of many kinds. Further, it will contain a considerable quantity of lime, and also magnesia, manganese, and phosphoric acid. In plants, the greatest amount of nutriment, including potash, is contained in the young growth, and not in the woody portions. Hence the richness of young grass, prunings, and trimmings from hedges, etc. In the mineral ash remaining When wood is quite consumed the potash in the form of a carbonate readily absorbs moisture and quickly runs away. The leached ash will contain most of the other minerals, but to preserve the potash wood ashes must be stored in a dry place before leaching takes place.

-WM. C. HYDE.

Horti-

culturist, Wellington.