THE FARM.

Pukekohe & Waiuku Times, Volume 4, Issue 96, 15 October 1915, Page 4

THE FARM.

Farm Drainage.

By A. McTaggart, M.S.A

(Reprinted from the "Journal of Agriculture ")

The first requisite in Ihe treatment of a 6011 so that it will effectively grow a crop—be it cereal, root,' tuber, legume, grass, or fruit—is to attend to that important physical factor, drainage.

In this lirid of normally copious rainfall tbe effective draining of the tsoil is essential for tbe full development of the agricultural lesourccs of the country. True it is that the areas of greatest preciiitatijn, situated more particularly along our western, southern, acd roulh-eastein coists, are most in need of drainage; also, that tbe swamp areas, tie si iff clays, the lands with more or less impervious subsoil, and other soils waterlogged fcr either continuous or intermittent periods, call most urgently fur the handicrafc of the drainer to render them fertile or to increase fieir fertility. But there are few from among our great range of soil typss that will not respond to drainage operations systematically conducted. Even hillside soils, more especially if of clay or clay-loam formation, can be benefited by a modified system of extracting the surplus water from the soil. Land* that are sometimes erronrouely thought rot to require drainage frequently riiow marked results when systematically treated fiom this physical standpoint, either by providing them with a complete drain arrangement or by augmenting t-,e existing drains by means r.f intermediate water channels. UNDERLYING PRINCIPLES.

The benefits to be derived by the soil from effective drainage are many, and the more important may be beie outlined before proceeding to deal with actual methods and the practice of draining. A drained soli is more porous, a decidedly important fact, for an open soil with under-drains permits .he surplus water to get away readily, and hence there is Bet up a free circulation of air -instead of stagnant conditions. The air following into the soil promotes the formation of available plant-food in tie form of nitrates, and aids trn germination of seeds, consequently stimulating the growth of plants. In a poorly drained roil the air is almost entirely excluded," for the pores are full of water, thus preventing germination and plantgrowth from proceeding in a beathly manner. The email quantity of air in the pores pregnated with water soon becorms impure, sinus the roots give off poisonous substances, and the fubstitution of fresh or impure air is slow, owing to tie smallness of the pores. The veotilathn of a well drained soil with is larger pores, however, is much more rapid and tin soil-air much purer. Effective under drainage being provided and the air being admitted freely into the soil, there is act up a free circulation. The air over the surface of the ground heats rapidly under the strengthening waimth of the sun's rays, and this circulating through the sill causes the soil particles, especially in the surface layers, 10 absorb heat, plant growth being etimulated thereby. This is nf special importance in the spring, when new growth begins to appear, for a favouring factor like thorough diainage is then specially desirable. It has been calculated that a drained soil is warmer thin an undrained in the spring time by from 5 (o VI degrees. The beat received from ihe sun is used h three ways: some of it evaporates water from the soil, some heats the surface layers or seed bed, and the remainer is conducted to lower layers. It is not fully realised how much of the sun's heat is used in evaporating water from the soil. As long as the latter lojks wet on the surface evaporation is going on about as rapidly as from i'rea water, and the amount of heat used by it luns from 25 to 50 per cent, of the txtal amount received from the sun. This at a time when warmth is needed to germinate crop seeds h a serious loss. As soon as the eoil begins to look dry en the surface the ra'.e of evaporation falls off materially, and much of the heat formerly used jn turning water into vapour is available for beating the surface layers. Undrained soil, being the more compact, remains moist n the surface, and evaporation from it continues at full speed long after it his been checked on the paious drained land. Moveover, loose soil is a poorer conductor cf heat, and hence carries less of it down to the l:wcr layers. The nifferenc? arising from these conditions is accentuated by another cause. Water is the hardest knorn substance to heat, and since during most of the time the undrained soil is too wet and has more water in it than th». drained, it follows that it must be colder. With the drained land saving heat because evaporation is checked, conducting less to the lower layers, and at the same time being easier to heat the temperature of its seed bed is easily maintianed from 5 to 12 degrees higher than that of the undrained, . . .

Effective drainage, by lowering the permanent water-tat-13 and setting up greater pore-space, enables the routs of a phnt to P'jn t:ate more deeply ia search of fuod and moisture. Ibus tbe feeding puwer, hence productiveness, of a plant is enhanced. The plant baa also greater foothold and penetrating power, and can more or less withstand adverse conditions sucb as high winds and dry periods. When roots cf deep-rooted plants decay tbey provide humus for the lower reaches ot the surface soil, also air passages wbicb increase the aeration and ventilation.

Tbe first and one of tbe ipmortant results ot toe difference in temperature caused by drainage is that seeds germinate better. Every kird of seed has a temperature at which it germinates better than at any other. At tco low temperatures many of the seeds will not germinate, and those that do grow very slowly. Drainage overcomes this slow incomplete germination. Owing to its higher temperature,, coupled with the presence of more freab air, tbe drained soil is supr-rior to undrained in another way. Scil contaios myriads of bacteria, and these mnute organisms prepare the food for plants. By their agency soil-constituents and manure are transformed into salts, which dissolve in water and with it pass into the roots to sustain the plant. 1 hese bacteria need fresh air as much as plants or aoin.als do. In the drained land th:re is plenty of it. Moreover, a congenial temperature is needful ai much to them as to man, and this, too, they find in the drained soil. Here, then, they thrive and flourish, combining thj elements of the air with those of the soil, and give to tbe plant abundance of food made to its own liking. In the undrained soil, however, the s:ant supply of air becomes impure, and this, together with the cold, renders moat of them so inactive that but littls plant food is prepared; one of the vari.its, indeed, is so constituted that when air is scarce it ilves on tbe lood already fitted for the plant. It follows readily that the amount ot plat. Wood available in drained far exceeds that in undrained land, while tbe more extent ive root systems in the former enable the plants to make full use ot this advantage. Ari-ing out of these various special advantages of drainage are the larger practical benefits, being tjiose of greatly increased productiveness, ability to cultivate or facilitate cultivation, and the promotion of healthier stick.

There are certain general indications that point to the need of a soil lor drainage. These are tbe presence of rushes, sedges, and other wat-r-lovirg plants; the tendency of pasture to run (0 the inferior bent grasses (florin, redtop, etc), or to other inferior grasses and weeds; tbe yellowing and disappearing of clovers, and a non-thrifty condition of pasture generally.