DORMANT WEED SEEDS

Hawke's Bay Tribune, Volume XVII, 26 November 1927, Page 12

DORMANT WEED SEEDS

HOW LONG CAN THEY SURVIVE It is a fairly common belief that if land which has not been stirred for a long period is ploughed up a largo crop of arable weeds, which were not. seen in the pasture, will spring up thefollowing year, and in such numbers as to preclude their having been brought there by such common means as birds or winds. There is obviously much truth in this belief, but close investigation has shown that most of tho authentic cases havo been on lands which had at some tine or olhor been under arable cultivation and were not real old pastures. If very old pasture be ploughed up it is improbable that arable weeds will appear to any very great extent tho first year. Soma few seeds, as those of groundsel! sowthistle and dock, may be carried by the wind, and other arable weeds may bo introduced by tho crop seeds, etc., so that, in the course of a very few years, even bokon-up pasture can become colonised by a typical arable weed flora. If more recent pasture 30 or 40 years old, be broken up. tho case is different. The seeds of certain weed species are capable of lying dormant in the soil long periods of years, and of germinating when the land is broken up and conditions of growth become favourable. Most of tho weed seeds in the top few inches of soil tend to germinate, although the land is grassed over and tho •seedlings are stifled by the grasses and clovers. Consequently, there are less terminable word seeds in these top inches when the land is ploughed. Seeds in the lower depths are unable to germinate especially from five to nine inches, owing to unfavourable conditions. ’These seeds retain their power of growth for a long time, but they gradually di e off with the pro gress of time. The length of time such seeds cun lie dormant varies with the species. There are, again, usually fewer seeds in the ’ lowest three inches, because under ordinary conditions of cultivation only about nine inches of tho soil is well worked and any seeds >n lower depths nave had to work their way down through cracks and crannies and worm-holes inf/. tho harder layers of the subsoil. In dealing with remedies it must not be forgotten that land under ordinary farm tillage contains great numbers of arable weed seeds capable of growing, especially in the top seven inches of soil, which is best cultivated. These seeds do not ne cessarily all germinate the year after they are shed, but a certain proportion Ho dormant for varying periods nud start into life among Inter crops'. The methods of cultivation and manuring havo an important benring on the number of weed seeds that are present in the soil. Root crops are valuable aids in cleaning the land, ns the constant hoeing not only cuts off the young seedlings, so clearing the land for the standing crop, but also prevents tho weeds from forming seeds, so that later crops are likely to bo freer from weeds.