HUMUS IN SOILS.

New Zealand Herald, Volume LX, Issue 18457, 21 July 1923, Page 16

HUMUS IN SOILS.

REPLACEMENT NECESSITY.

; The fertility of the soil is dependent upon several distinct factors,' sorao of which it is within the power, of man to alter: some cannot be changed. The physical properties and the chemical conditions are the two points which are most easily influenced by good husbandry. Manuring, whether by artificial or stable waste, increases the amount or! plant food, but unless the mechanical condition of the soil is suitable full use cannot be made of this food. In humus we have something which alters the mechanical end chemical conditions of thfl soil, but not only does it make a stiff clay more porous and a sandy soil more retentive, but it also replaces plant food, and from its sponge-like properties prevents undue wastage down the drain. ." •

Humus is one of the most important constituents of virgin soil, and humus carries With it a considerable amount of nitrogenous matter, which in unavailable form., is easily released for the benefit of crops when conditions for the changes needed are improved as they are by tho putting of the land into cultivation. On virgin soil in wooded lands the leaves fall year bv year, branches droop, the trees die, their roots, which have penetrated deeply into the soil, decay also, and with Mich life and death over a period of years there is made a soil which is rich in vegetable matte 1 . On the plains grass grows year after year, and dies down in *be late summer and autumn, and after a number of years we find an *cn»j«?tsS>v-Jow ; of the vegetable matter w d;* - .■■■:■- .MC ■■•• ment of goort 5---j*. ' J r- *.■':■■ --^_'"'>'"• wv* i>\--f ' & combii'fttic' >:■■ :■. i(• ■■';: *';'.'-i ,:\-; : 'v *>«.- ; lP;.i«tur«-';OT'' r .' rV.V. -': :';-it ■'■'■'• ';■•:/ tWV Pjv! ■': ■■•■:-■■ •- ■h-:-C'-y i'~: -if- the low pliiCeS • :.~;\ ii.aiu> n-:n ■'"■< ■-'•:'• *e Hud that prac- .■"•!'• :l : . ?-.-.:■ jiif. are the result of plant *#-.*«■'!•"«: :• ■ ,i death and the accumulation of the vegetable matter which is not entirely decayed. Precisely what humus is no one can exactly say, though some'of its component parts have been identified and named by chemists. The definition generally given is that it is decaying vegetable matter in the soildecaying and not decayed, as then its transformation would be complete and its. work done. TV is made up of a humbe' r.f ■;' ''> ■;•■*•nt <•> . uuations, in all of w>, .. ( '.a u.-irog- 1 . ':& 'a& insoluble form and is u.. result. > 'itay under conditions inimical to uhorough decomposition. When the land is put into cultivation better conditions for decay are provided and the humus is used up in a few years, faster in some regions than, in others. The conditions favouring the breaking up of humus or of any organic compound in the soil are plenty of air, heat, moisture ar.d alkalinity, which ' favour the action of the organisms assisting in the decay. Air.may be excluded by water, or, in a measure, by tho compactness of the soil; heat, is not sufficient in cold, wintry weather: moisture may be excessive. or it may be lacking because of exposure to wind and sun ; acidity, though sometimes high in swamp soils, usually is not high' enough to interfere with' some of the organisms that are associated with decay. » - J,' Cold weather." tends" Jo 'check the lo§s, of humus and to favour humus formation. On land' that is in perennial meadow and undisturbed for several years there is. like effect. Probably more of 1 the root's and stubble is -used in true humus"formation, but the vegetable matter, whether forming humus or not, gives off something of the benefits of humus in the betterment of the physical nature of our- soils, the increase in water-holding capacity and in the supply of nitrogen. We might say : that humus in virgin soil is a bank' v account of ;lon;g- .standing";; against which" we draw," soon depleting the account or reducing our "balance," while the vegetable matter we supply to soils under continuous cultivation is more like a merchant's capital that is turned over and oven in business transactions. We keep adding vegetable matter: 1 to the soil-and we are continually drawing it out and we may never get back to virgin soil conditions. All of -vis, therefore, are interested in the returning of vegetable matter to or/x soils. We have learned better than to burn our, old crop residues; unless necessary for the control of some pest. Humus must be recognised as one of the most important constituents of a soil. It must be recognised that it' is continually passing, into a valuable form of nitrogenic matter, which is utilised and withI drawn from the soil, and that' it must be i replaced fertility and good soil condi- ! tion is to be maintained.