WEEDS. [By Sir J. B. Lawes, Bart, LL.D., F.R.S.]

Waikato Times, Volume XXII, Issue 1829, 27 March 1884, Page 3

WEEDS. [By Sir J. B. Lawes, Bart, LL.D., F.R.S.]

It is very remarkable what totally opposite opinions may be held upon the same subject, more especially it that subject relates to agriculture. I have recently pointed out that where weeds and agricultural ciops grow together, not only would some part of the food which might produce crop be taken np by the weeds, but fuitber, if nitrate of soda were used, the pecuniary loss would be greater, be cause nitric acid was dearer than organic nitrogen ; and the oiganic nitiogen of weeds ploughed under the soil might possibly be several years before it all assumed the form of nitiic acid. In the Agricultural Gazette of October 15th a DewAshiie landowner, addressing his tenant^, is reported to have said :—": — " If a tenant kept his land clean theie was but little exhaustion ; weeds weie great exhatsteis, and if a tenant of his would agree to fai m clean under a penalty, he would give up many conditions as to the sequence of crops. " Ashoit time ago I went over a J.um which, being vacated by the tenant, was tin own upon the hands of the owner. A l.nge field of bailey had apparently been left uncut in consequence of the pioduce — which could only have amounted to <i very few bushels per acie — being uisufhcu'nt to pay the cost ot the opeiatiou. The cause ot the im^einMe crop was the amount of weeds, the most prominent being wild oats and mayweeds, the luxuriance of which supplied sufficient e» idt-neo of the good condition of the land. It is quite possible that the nitrogen in the weeds upon an acie of this land would have amounted to from 201b to 251b per acic, while the nitiogen in the bailey ciop would not have amounted to mote than 71b or 81b per acre. The wild oats, which ripen their seeds befoie the com is cut, and shed upon the lands while the straw is returned to the soil with the bailey straw. The m.iywecd would be ploughed in ; the only export of nitiogen, theiefore, would be that in the giain ot the barley, which would amount to about 51b. Let us now see what would happen as regards the exhaustion of the soil, under the relaxed conditions promised by the Devonshire landowner to a tenant who kept his land clean under a penalty. If there had been no weeds the produce of grain might have amounted to fiom 30 bushels to 35 bushels per acie, containing about the same number of pounds of nitiogen, which would be earned off the land. There can, I think, be no doubt that in this case, so far from exhausting the land of nitrogen, the weeds .stored it up in the soil ; as if theic had been no weeds, and only four or fixe bushels of barley, the nitric acid formed would have been washed out in the winter. If the " many conditions given up as to the sequence of ciops" included the permission to grow several corn crops in succession, it will be evident at once what would be the result. It appeai-3 to me to be quite impossible to maintain that weeds exhaust land ; on the contiary, they operate as one of the great economies of Nature, by filling e\eiy vacant space with vegetation. 1 may s.iy that if I wanted to exhaust land of its nitiogen as quickly as possible, I should either keep it entirely without vegetation, and stir it up frequently, or I should grow repeated corn crops with constant hoeing. In one case the land would be exhausted of its nitrogen, and in the other it would lose potasli and phosphate as well. In my first article on weeds I mentioned that in the conversion of purchasad nitric acid into growth the loss >vas more serious than if the source had been the nitric acid liberated from the organic nitrogen of the soil, The reason being that the amount of nitric acid liberated each year from the organic matter in ordinary sods does not cost so much as the purchased nitrate : or — as I have said on more occasions than one — the landowner sells fertility cheaper than it can be pui chased in its aitificial form. The best proof of this is the fact that when a farmer calculates the profit attending the application of an artificial manure— say of nitrate to a corn crop— he bases his calculation on the total inciease obtained by such application, leaving the ordinary crop to bear the whole cost of rent and cultivation. In explaining what appears to be the action of weeds, I must, however, warn your readers against thinking I am friendly to them. In our highly manured corn experiments at Rothamstead they have been — more especially during the last few years of excessive wet — a source of the greatest trouble and expense. The mischief they do to a heavy wheat crop, at the time of blooming and afterwards, is so great that it is a choice of evils— whether to leave the weeds, or injure the corn by removing them. The luxuriance of thr weeds upon the highly manured crops, and those where the application is confined to mineral manures alone, leave no doubt in regard to the identity of the food taken up by both weeds and corn.

Mr John Knoz will sell at bis Auction Mart on Saturdry next, chests tea, kerosene, fowls, plrs, ling fish, filter, and a choice collection of apples from Frankton — 215varteties. Also, on the same day, in the bankrupt estate of Beauchamp Bros., iron tanks, hydraulic ram and piping large boilers,' and in the estate of Henry and Allen, grindstone, ihoveli, ipadei, picks, fee. &c.