Intercultivation and Weeding

New Zealand Journal of Agriculture, Volume 73, Issue 5, 15 November 1946, Page 446

Intercultivation and Weeding

TN growing crops there is no practice which contributes more to I - i r • 1 • • 1 < 'l <7 V • success than proper inter cultivation and weed control. Nothing on a farm is more unsightly to those who know what it means to produce a good crop. economically than a weed-infested crop.

JETHRO Tull in “Horse Hoeing HusJ bandry,” published in 1731, wrote that “tillage is manure,” and the advantage resulting was a freeing of the soil particles. - He believed that the soil was the only food for plants and that the plants fed on; the minute particles. Therefore it was reasoned that the more finely divided the soil, the better would the plant be nourished.'

At ' the beginning of the nineteenth century the conception of plant nutrition was -based on the assimilation of chemical elements from soil minerals, organic matter, water, and air. The reason for cultivation was then given as increased aeration, which , in turn increased the’ oxidation of chemical compounds to make them more available . for plant use. Other theories were later put forward such as (a) stirring and mixing the soil to change the relationship of soil in regard to moisture, temperature, and plant food; (b) deep cultivation to allow roots to penetrate deeply for nutrients and water; (c) the chief benefit was control of weeds; (d) the primary aim was to pulverise and stir the surface of the soil after being hardened and caked by rain.

Today the following reasons for cultivation are held by many:-—’. 1. Destruction of weeds. 2. Conservation and storing 'of moisture. 8. Aeration of the soil.

Weed Control The prime factor in reducing intercultivation work to obtain weed control is good ploughing and skilled cultivation. before sowing or planting of the crop. “Skilled cultivation” means the doing of the right job at the right time with the right implement. All are not in a position to possess a range of implements to meet the requirements of all soils on their farms,' but it is possible to attain the same result with careful working of the more simple implements.

It should be the aim to germinate as many weed seeds as possible just before sowing or planting, and to stir the surface soil layer slightly to kill these with the harrows. On some soils in a dry period rolling will bring the moisture to the surface in sufficient quantity to cause germination of certain bad weeds such as red root (Amaranthus spp.).

Intercultivation should begin soon after the crop rows are easily distinguished, when any weeds present are-usually at the right stage to kill by cultivation, particularly when the vzeather is' dry. Many heavily weedinfested soils are in districts where it is exceedingly difficult to attain a good kill on account of the heavy moisture content and sticky nature of these soils, and in such cases one should question the wisdom of growing crops, particularly in those parts of New Zealand where grass production can'be relied on for almost all . requirements.

It has been found from experiments carried out at Rothamsted, England, that with potatoes there is no advantage in intercultivation in the absence of weeds. Where weeds were present there was a very marked sensitivity of the potato crop to competition. Experiments in the United States on maize crops confirm this and indicate the full importance of weed control. Trial crops with the same seed-bed preparation showed an average yield over an 8-year period of 7.3 bushels per acre where weeds were allowed to grow, as against 45.9 bushels per acre where weeds were kept down.

' The removal of weeds whether by hand hoe, by pulling, or by careful use of the cultivator has been proved to be the major factor in increased yields.

Moisture Control

Cultivation directed at weed control has a bearing on conservation of moisture as well as on , aeration. This tends to be more in evidence on heavier soils and those which become hard and baked on the surface. Cultivation beyond that needed for weed control appears to be not so necessary on the freer types of soils.

Very light cultivation »on the top inch or two of soil at the most is sufficient to conserve moisture in periods of dry weather. With ■ the variety of tines and shovels available on cultivating equipment it is possible to work up a good surface soil mulch. On sticky .or heavy ■ soil types the larger shovels should be avoided and use made of the- chisel-teeth type. Where the soil is relatively free the shovel type can be safely used.

. As well as loss of moisture through evaporation there can ' be a loss through surface run-off. The mulching of the surface layers will reduce this to a minimum. It is desirable to have a granular soil mulch rather than a fine, or dust mulch, as . a granular mulch is not so likely ,to form , a crust after a . shower and also breaks the capillary rise of water more effectively. Aeration

A well-aerated soil is most favourable for bacterial activity. Air is also necessary for certain chemical and physical changes in the soil in making plant nutrients more available and improving tilth. Cultivation stirs and turns the soil in such a way as to keep the air well distributed. Again, the greater effect of cultivation on aeration is found with the heavier types of soil. The beneficial effect of cultivation on aeration is less marked with the more open types, hence the need for more careful cultivation of crops on heavier and more sticky soils.

It • is apparent that intercultivation is necessary ■in producing a good crop, and it is much more profitable to grow 1 acre well than 2 acres of only half a crop. For aeration the number ,of cultivations required will vary with conditions; in dry seasons it is necessary to cultivate more frequently than in wet seasons.

The depth of cultivation depends on the type of crop and the soil. Where root crops are grown cultivation can be deeper with little danger to the roots, but in a crop such as maize there is real danger of pr,uning surface roots which extend for long distances near the surface. It is interesting to note that at whatever depth the maize seed is planted the crown or secondary rooting system always develops at about the same depth, just below the surface. It is on this root system that the maize - plant depends during its later growth. Cultivation sufficiently deep to prune these roots will reduce the ultimate, yield of the crop. With these roots so near the surface it is evident that shallow cultivation is all that is required. ;

Experiments so far carried out have shown very important differences in favour of shallow cultivation, and it would appear generally that cultivation as often and as deep as is necessary to control weeds is best. /

If in the cultivation, of crops the aim is to keep all weeds destroyed and to keep the surface of the soil mulched, it is necessary to cultivate as soon after each rain as practicable. The time and number of cultivations required by any crop will vary with the season and the soil. 7

J. R. MURRAY,

Instructor in : Agriculture, Hamilton.