546

BULLETIN No. 546

Contribution from the Bureau of Plant Industry

Washington, D. C.

WM. A. TAYLOR, Chief

PROFESSIONAL PAPER

June 27, 1917

EFFECT OF FALL IRRIGATION ON CROP YIELDS AT BELLE FOURCHE, S. DAK.

By F. D. FARRELL, Agriculturist in Charge of Demonstrations on Reclamation Projects, and BEYER AUNE, Farm Superintendent, Western Irrigation Agriculture.

One of the conspicuous features of the climate of the Great Plains area is the light precipitation received during the winter months. Throughout most of the Plains region, about three-fourths of the annual precipitation occurs during the six months from April to September, inclusive,' so that the winter months are, comparatively, very dry. As a result, it is commonly found that after producing a crop the land remains dry from harvest time until the rainy season of the following year. The soil on such land during this period may be deficient in moisture not only near the surface but throughout the zone of action of the roots of crop plants. It has been assumed that this soil-moisture deficiency might have an unfavorable influence on the growth of crops, both by hindering the germination of springsown seed and by retarding or preventing the desired movement of the water received as precipitation or applied in irrigation during the growing season.

The practice of fall irrigation-the application of water to the land in the fall of the year-has been advocated as a corrective of this condition in irrigated regions. Various writers on irrigation. have suggested the desirability of fall irrigation, and a few investi

1 Briggs, L. J., and Belz, J. O. Dry farming in relation to rainfall and evaporation. U. S. Dept. Agr., Bur. Plant Indus. Bul. 188, 71 p., 23 fig., 1 pl.

85963-Bull. 546—17

1910.

METHODS USED IN THE EXPERIMENTS.

The experiments were conducted in field P, Series I, II, III, and IV, seven tenth-acre plats being used in each series. A diagram of these plats is shown in figure 1. The land was first broken in August, 1911, and it produced oats in 1912 and again in 1913. It is uniform in topography and soil. The crops of 1912 and 1913 were harvested from the field as a whole, no record having been secured of the production of the different series of plats. Series II and IV were irrigated on November 11, 1913, November 11, 1914, and November 10, 1915. Except for this fall irrigation, the treat

FIG. 1.-Diagram of a part of field P, Belle Fourche Experiment Farm, showing the location of the plats used in the fall-irrigation experiments. The arrows indicate the direction of the flow of the water in the irrigation laterals supplying these plats.

ments applied to Series II and IV were uniform with those applied to Series I and III.

The fall irrigation was applied each year after the plats were plowed, except that in the autumn of 1914 the plats which that year had produced intertilled crops were not plowed. Low earth dikes were thrown up at the lower side of the plats to impound the water sufficiently to insure a complete covering of the land. The water was then applied by flooding and allowed to run on each plat from three to four hours. The summer irrigation of each crop was uniform on all four series as to both time and method of application. No attempt was made to measure the water applied, but the methods of irrigation recognized in the locality as good-farming methods were followed. The sugar beets and potatoes were irrigated by the furrow method and the other crops by field flooding.

The experiments were conducted in duplicate each year, the seven plats in Series I duplicating those in Series III, while the plats in Series II and IV were duplicates. The following crop varieties were used: Oats, Great Dane in 1914 and Swedish Select in 1915 and 1916; sugar beets, South Dakota No. 40 in 1914 and Kleinwanzleben in 1915 and 1916; flax, Minnesota No. 25; potatoes, Eureka in 1914 and 1915 and U. S. No. 4452 in 1916; barley, Minnesota No. 6 in 1914, Himalaya (Guy Mayle) in 1915, and Chevalier in 1916; corn, Payne White Dent in 1914 and 1916 and Martens White Dent in 1915; and wheat, Defiance in 1914, Pringle Champlain in 1915, and Marquis in 1916. The positions occupied by the crops on each of the four series each year, the crop sequence on each plat during the 3-year period, and the number of summer irrigations applied are shown in Table II.

TABLE II.-Sequence of crops and number of irrigations applied to each in the fall-irrigation experiments at the Belle Fourche Experiment Farm in 1914, 1915, and 1916.

As shown in Table II, an intertilled crop followed a a close-planted crop on each plat except No. 13 in 1915 and 1916 and No. 10 in 1916. More irrigation was necessary in 1914 than in either 1915 or 1916, as the growing season of 1914 received somewhat less rainfall than either of the others. The variations in both crop sequence and summer irrigation were the same on all four series.

All cultural operations on the four series were uniform as to both character and time of performance throughout the period of experiment. These included the ordinary operations incident to the production of the seven field crops involved. The land was manured from October 6 to 10, 1915, when 12 tons per acre of well-rotted barnyard manure were applied uniformly to all the plats.

RESULTS OF THE EXPERIMENTS.

In the conduct of these experiments attention was directed chiefly to the crop yields secured on fall-irrigated land as compared with those of land not so irrigated and to the soil-moisture conditions on the two groups of plats, particularly before the first summer irrigation each season. It was to be expected that any important

differences in the yields of the crops on the several plats would be associable with soil-moisture differences in the spring, as the only variation in the treatment of the land was the irrigation applied to half the plats in the fall of each year.

CROP YIELDS.

Two plats of each of the seven crops were grown each year on the fall-irrigated land, and the same number were grown on check series, the latter receiving no fall irrigation. The yields are reported in detail in Table III.

TABLE III.-Yields of crops in the fall-irrigation experiments at the Belle Fourche Experiment Farm in 1914, 1915, and 1916.

In order to facilitate comparisons of the yields shown in Table III, (the figures have been calculated in percentages, and the relative yields are shown in Table IV, in which the yields of the check plats are represented as 100 per cent. The yield shown for each crop is the average of duplicate plats.

TABLE IV.-Relative yields (expressed in percentages) of crops in the fall-irrigation experiments at the Belle Fourche Experiment Farm in 1914, 1915, and 1916.

The figures in Table IV show that in 1914 the yields of wheat, barley, and corn were higher on the fall-irrigated plats than on the check plats, the increases being 37, 2, and 1 per cent, respectively, while the yields of the four other crops were lower on the fall-irrigated land, and that the average yield increase of the seven crops in that year was 2 per cent in favor of fall irrigation. In 1915 the yields of all the crops were lower on the fall-irrigated land, the average decrease being 11 per cent. In 1916 all the crops yielded less on the fallirrigated plats than on the checks, except potatoes, which yielded 5 per cent more. In the 3-year average, wheat on fall-irrigated land showed an increase of 10 per cent, while all the other crops showed decreases ranging from 3 to 10 per cent, the average yield decrease of the seven crops on fall-irrigated land for the 3-year period being 4 per cent of the average yield of the check plats.

The fact that of the 42 duplicate plat averages secured in the 3-year period only four were in favor of fall irrigation would support a presumption that fall irrigation on this soil was detrimental. However, since not all the yields were against fall irrigation, it is possible that the yield variations were accidental. In order to determine whether these differences were significant, the probable errors of the average yields have been calculated. The results are shown in Table V, in which the yields secured during the 3-year period are summarized. TABLE V.—Summary of the yields secured in the fall-irrigation experiments at the Belle Fourche Experiment Farm in 1914, 1915, and 1916, showing the probable errors of the

The figures in the last column in Table V show for each of the seven crops the difference between the average yield of the fall-irrigated plats and that of the check plats during the 3-year period. None of the differences was as great as the probable error, so that all must be regarded as insignificant. A similar tabulation of the yields of straw and stover (which are not shown here) produces a like result, there being no significant differences in the average yields of these products.

The explanation of the somewhat lower average yields secured on the fall-irrigated land lies in the relatively low productivity of Series