(3) Weeds evaporate water. The demand of the maize plant for water is so great at certain periods of its growth that the possibility of development and yield is fixed by the supply of water available. (280) If this supply of water is in any way reduced by the growth of weeds, the yield of maize must be reduced. Sturtevant observed the difference in practice among the vineyardists in New Jersey. Those on the low lands allow weeds to grow: on the uplands the soil is kept free of weeds. The inference is that the weeds pump the water out of the wet land to the advantage of the grape, which prefers a dry soil.

310. The Effect of Stirring the Soil is to break the roots in the area stirred and to make the soil in this area looser, otherwise change its structure and to bring particles of soil into different relations one to another. This allows air, water and roots to enter more freely. The amount of water, the temperature, and probably the salts in solution are affected thereby. (297) King found that cultivating three inches deep made the soil .4 to 1.1° F. cooler than cultivating 1.5 inches deep.1

311. Root Pruning.-It has been clearly demonstrated that any mutilation of maize roots has an injurious effect. At the Illinois Station2 pruning three to four times during the ordinary season on all sides six inches from the center of the hill to a depth of four inches reduced the yield of grain from ten to thirtytwo per cent, the average decrease for five years being twenty per cent. The greater percentages of decrease were during seasons of least rainfall. Pruning three inches deep one season caused a decrease of five per cent. The Oklahoma Station3 found during one season no injury from running a knife three inches deep six inches from the hill, or six inches deep twentytwo inches from the hill, but when the knife ran six inches deep six or twelve inches from the hill the yield was much reduced.

1 Wis. Rpt. 1893, p. 192; 1894, p. 283.

2 Ill. Buls. 13, 25, 31.

3 Okla. Bul. 36.

The New York State Station found a decrease in grain of twenty-eight per cent and in stover of twenty per cent during a dry season, pruning three inches deep three to four inches from the hill. During a rainy season pruning in the same manner the second and last time when plants were only ten inches high decreased the yield of grain seventeen per cent and the stover twenty-three per cent.

312. Depth of Cultivation.-While the experiments in root pruning suggest that decided injury would result from deep culture, they do not show what influence stirring the soil might have in counteracting such injuries. Not less than nineteen

Sixty-one tests of deep cultivation at thirteen stations gave an average yield

stations have made tests of deep and shallow culti vation, as shown in table A on preceding page.

B

of sixty-five bushels, while fifty-five tests of shallow culture gave seventy-five bushels per acre, a de crease of thirteen per cent

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. Bul. 33, p. 63.

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 culti

vetor, 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 Ill. Bul. 31, p. 356.

no maize was obtained. This experiment has been verified by the New Hampshire1 and Utah 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:

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. Bul. 71 (1900), p. 50.

2 Utah Bul. 66, p. 108.

3 Okla. Bul. 63 (1898), p. 4. Ga. Bul. 58 (1902), p. 208. Kan. Bul. 64 (1897), p. 23. Ohio Rpt. 1888, p. 87. N. H. Bul. 71 (1900), p. 51. So. Dak. Rpt. 1900 (E. S. R. II: 511). Mich. Bul. 164, p. 90. Wis. Rpt. 1894, p. 282. Md. Bul. 62 (1899), p. 195