« AnteriorContinuar »
due to deep cultivation.1 Most of the stations have considered one to two inches deep, shallow cultivation, and four or more inches deep, deep cultivation. In some of the trials where deep cultivation was found the best, notably at the Wisconsin Station, deep cultivation was only three inches deep, and in the average of twenty-one trials was only one per cent
1 Miss. Bui . 33, p. 63.
stations have made tests of deep and shallow cultivation, as shown in table on preceding page.
of sixty-five bushels, while fifty-five tests of shallow culture gave seventy-five bushels per acre, a decrease of thirteen per cent
Tools for the shallow cultivation of maize. A, onehorse cultivator with three broad shovels in rear, the width and depth being adjustable, requiring the passage twice to cultivate a single row; B, two-horse walking cultivator, with broad knives for complete surface tillage, cultivating a single row at each passage; C, two-horse riding cultiv tor, shallow cultivation being secured by four, sometimes five, small shovels on each side, the depth being adjusted by means of levers shown above frame; cultivates a single row; D, threehorse riding cultivator for cultivating two rows at one passage.
greater than when cultivated one and a half inches deep. Studies of root growth of maize made at the Illinois Station indicate that fifty per cent more roots may be cut off at four than at three inches deep. The evidence in favor of shallow cultivation is even more conclusive, therefore, than the table indicates. While the evidence seems to show that the breaking of the roots while the plant is less than six inches high is not so serious as at later periods of growth, and that plowing deep at the first cultivation is not so injurious as at a later date, yet, on the other hand, evidence does not indicate any special benefit from such deep culture in the majority of cases. Doubtless something will depend upon the previous preparation of the seed bed. If the seed bed has not been properly prepared before planting, or if the land has become extremely compact from heavy rains or otherwise, a deep cultivation while the plants are quite small may prove beneficial, but the evidence clearly indicates that in the majority of cases shallow cultivation at all times will give the best results, provided such cultivation is equally effective in eradicating weeds. In practice, shallow cultivation has been found equally effective in destroying weeds, provided the weeds are not allowed to get too large, in which case deeper cultivation sometimes becomes necessary.
313. Amount of Cultivation.—The injury from root pruning has generally been greater than injury from deep cultivation. This may be due to the cultivation having injured less roots or to the beneficial influence due to stirring the soil. During five years the Illinois Station1 cultivated a plat two inches deep and four inches deep, while on an adjacent plat the weeds were removed by scraping the surface with a sharp hoe without breaking the crust of earth. The average yield was, deep, sixtysix bushels; shallow, seventy-two; none, sixty-eight bushels. During two years on one plat where weeds were allowed to grow,
1 11i. Bui. 31, p. 356.
no maize was obtained. This experiment has been verified by the New Hampshire1 and Utah 2 Stations.
Plats were also cultivated from three to five times a season in comparison with plats cultivated about three times as much. The averages for five years are as follows:
Bushels grain per acre
Shallow, ordinary 7°-3
Deep, ordinary 66.7 Shallow, frequent 72-^ Deep, frequent 64.5
Frequent, average .... 68.6 Ordinary, average .... 68.5
Eight other stations have found similar results, while the Michigan Station found that frequent cultivation gave a yield of twenty-five per cent more dry substance than infrequent culture.3
No advantage has been found in cultivating maize after the plant is three to four feet high, provided it is free of weeds at that time; and cultivation to prevent subsequent growth of weeds has not materially increased the yield, and when cultivation was deep, has decreased it.
314. Conservation of Moisture: Influence Due to Stirring the Soil.—It has been shown that allowing the weeds to grow almost prevents the growth of maize; that when weeds are removed no stirring of the soil gave better yields than deep stirring; while shallow stirring gave better results than either no stirring or deep stirring, while finally stirring two or three times a week gave about the same results as stirring once a week during the
1 N. H. Bui. 71 (1900), p. 50.
2 Utah Bui. 66, p. 108.
8 Okla, Bui. 63 (1898), p. 4. Ga. Bui. 58 (1902),p. 208. Kan. Bui. 64 (1897), p. 233. Ohio Rpt. 1888, p. 87. N. H. Bui. 71 (1900), p. 51. So. Dak. Rpt. 1900 (E. S. R.II: 511). Mich. Bui. 164,p.90. Wis.Rpt. 1894,p. 282. Md. Bui.62 (1899),p. 195. usual period. Aside from its influence in destroying weeds, which appears to be the main purpose of all intercultural tillage, a moderate amount of stirring to a depth which will not seriously injure the roots appears, therefore, to be somewhat beneficial.
If two inches of cut straw are spread upon the surface of the soil, the evaporation of water from the soil will be checked. If the surface of the soil is sheltered from rain, but exposed to the sun, and at the same time stirred to the depth, say, of two inches, the stirred portion rapidly becomes dry, and when in this condition acts as a mulch to the soil below, although not as effectively as does the cut straw. Under the above conditions the author has checked evaporation of water from the soil equal to onefourth of an inch of rainfall per week.
When, however, the soil is exposed to the usual atmospheric conditions of the humid regions, where it rains one day in three, it becomes a question whether the evaporation from the lower soil is checked more than that from the stirred portion is increased. The author has concluded from pot experiments conducted during three seasons that for humid regions during ordinary weather these two factors were nearly equal, although during rainy weather the evaporation may be increased and during periods of severe drouth it may be decreased by constant surface stirring of the soil, both of which may be desirable. The average evaporation in inches of rainfall from two pots treated as indicated below was determined for eighty-six days during the months of June, July, August and September at the Pennsylvania Station:
Evaporation in Inches of Rainfall During Eighty-Six Days.
Water. ....... 19.8
Bare soil not cultivated .... 16.0
Bare soil cultivated . . . . . 16.7
One maize plant, soil not cultivated . . 19.3
One maize plant, soil cultivated . . . 18.8
One maize plant, soil mulched with cut straw 10.6
Oats followed by oat stubble . . . 27.7
In these experiments only the loss of water from evaporation was determined. The looser soil will absorb more of the rainfall and thus lessen the amount that runs off the surface. This is especially true of compact clay soil and those having considerable slope. Generally, but not always, the looser soil will hold the most water and retard its falling beyond the reach of the roots. Since the trials which have been made indicate that surface cultivation is better than no stirring, and since occasional stirring has given as good results as frequent stirring, the inference is that so far as the conservation of moisture is concerned the most important effect of stirring the soil is to enable it to absorb and hold the rainfall.
315. Hilling and Bedding.—Some throwing of the earth towards
the row is often necessary in order to cover and destroy weeds. On all well-drained soils, hilling does not give any better results
poorly drained bottom lands of the Southern States bedding is practiced to give surface drainage. The Mississippi Station1 recommends that the beds be made eight feet wide or wide enough for two rows with water furrows in the alternate rows.
1 Miss. But, 33.