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296. Time of Plowing.—The evidence appears conclusive that the question of time of plowing relates to economic farm management rather than to differences in comparative yields. The experimental evidence on the subject of fall and spring plowing is meager and inconclusive. At the Nebraska Station1 much better yields of grain were obtained from plowing in September than in April, but no material difference was obtained from plowing in November than April. There are fine clay soils which become during the winter, if fall-plowed, so hard and compact as to make the preparation of a suitable seed bed at planting time a difficult task. Usually, however, the frosts of winter have a mellowing influence and increase the ease of preparing the seed bed. As fall plowing seldom affects the yield adversely, at least, it is generally good farm practice to plow in the fall those areas to which manure is not to be applied during winter and spring. Early plowing in the spring as compared with late plowing tends to conserve the soil moisture both by preventing evaporation of water and by increasing the amount of rainfall held.
1 Neb. Bui. 54.
Quiroga has shown that early plowing as compared with late plowing may not only increase the percentage of moisture in the soil and the yield of maize, but that the nitric nitrogen in the soil may be considerably increased. The available nitrogen in parts per million of dry soil was found to be as follows:1
On the other hand, early plowing decreases the amount of organic matter which will be incorporated in the soil if the land is in sod or a cover crop. Where the land is badly infested with perennial weeds, such as the bindweed or morning glory, late plowing destroys the growth already started and gives the maize plant a chance at least to start even. When the land is plowed immediately before planting, it may be at once dragged or rolled and then harrowed and planted while the surface is still fresh and moist. When the plowing is done earlier in the spring the surface requires working at once to prevent it from becoming hard, thus generally increasing the amount of labor to get a good seed bed.
297. Depth of Plowing.—While the variation in the depth of plowing seriously influences the cost of raising maize, since the draft of the plow is nearly proportional to the amount of soil turned, yet the investigations on this subject are quite unsatisfactory. In only one instance has a station reported results on depth of plowing for more than one year upon the same land. Undoubtedly the best depth will vary with the soil, the climate, the season, often with the previous crop grown, and the applica
1 Ohio Stats University Bui. Series 8, No. 28.
tions made (291); but no rules can be laid down as a guide foi general practice. The following table gives the results of trials on widely different soils under widely differing climatic conditions:
In all cases the plowing was done in the spring, except at the New Hampshire Station, when the land was plowed November first. In the first trial at the Illinois Station, in place of the usual intercultural tillage, the weeds were removed by scraping with a sharp hoe with the least possible disturbance of the soil. An adjacent plat, not plowed but disked one Inch deep, yielded 56.4 bushels of grain. The land on which this experiment was conducted had not been plowed in two years.
At the Pennsylvania Station a timothy and clover sod was plowed. At the fourinch depth the sod did not cover well and the shallow cultivation (two inches deep) which all plats received did not eradicate the grass on plats plowed only four inches deep.
While in a number of trials satisfactory results have been obtained by plowing four inches deep and less, yet the most generally satisfactory depth, all things considered, would seem to be six inches. As compared with wheat and oats, deep plowing is advisable.
1 All results are in bushels of grain per acre, except in the case of New Hampshire, where tons of green fodder are given. I Depths were 3, 5, 7 and 9 inches. • Also subsoiled 6 inches deeper. t Depths were 3 and 7 inches.
298. Subsoiling, or the loosening of the subsoil without bringing it to the surface, usually to a depth of twelve to eighteen inches, has been tried by a large number of stations. In some cases benefits; in other cases injury, both generally slight, but in most instances no material difference, has resulted. Subsoiling is nowhere a common practice, and the experiments so far conducted would lead to the conclusion that it will be found profitable for maize in humid regions only in exceptional cases. Indeed, in humid regions there is danger of puddling the subsoil, especially in the spring, where the subsoil may be quite wet while the surface soil is in condition to plow. In a co-operative test with fifty-nine farmers for three years, the Nebraska Station1 concludes that in Nebraska subsoiling is beneficial on clay subsoils and useless or injurious on loam subsoils.
299. Preparing the Ground After Plowing.—Fall-plowed land is left without further preparation until spring, as this exposure aids weathering and the absorption of moisture. As soon as the surface begins to dry out in the spring it may be pulverized in order to give it a mulch, and thus prevent the soil from drying out and becoming hard. When land is spring-plowed, the upturned clods will, during a dry time, become exceedingly hard and difficult to pulverize. To prevent this, the surface should be pulverized before the drying has proceeded too far. Usually it is best thus to treat each day's plowing on the day it is done. This may be done with a wooden drag, a smoothing harrow, or even a roller.
A deep loose seed bed, with all large lumps pulverized, is desirable, but fineness of pulverization is not so important as in wheat. The three tools most generally useful in preparing the seed bed are the wooden drag, the disk harrow and the light smoothing harrow. The roller may replace the drag, and the spring tooth harrow may replace the disk harrow, especially on
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stony ground. Precise rules cannot be laid down as to number of times or the order in which these tools will be used, since this will depend largely upon the character and condition of the soil, which must be determined upon the spot.
Very much depends upon performing each tillage operation when the soil is in just the right condition. Two hours of sunshine will often make the difference between success and failure in the operation of a tillage implement. This is what is meant in part by the couplet:
He that by the plow would thrive Himself must either hold or drive.
After the maize is planted, the land should be harrowed once, at least, with the smoothing harrow before the plant is out of the ground, and on many soils may be successfully harrowed after plants are well up. This second harrowing should not be given just when the maize