.AM S3 INITED STATES DEPARTMENT OF AGRICl BULLETIN No. 881 Contribution from the Bureau of Plant Industry • * _ J\^^^U WM. A. TAYLOR, Chief iCT^SOL Washington, D. C. T August 10, 1920 EFFECT OF ALFALFA ON THE SUBSEQUENT YIELDS OF IRRIGATED FIELD CROPS. By C. S. Scofield, Agriculturist in Charge, Office of Western Irrigation Agriculture. CONTENTS. Page. Aim of the experiments 1 Description of the experiments 2 Results of the experiments 3 Irish potatoes 3 Results of the experiments— Continued. Oats 7 Sugar beets 9 Summary 12 AIM OF THE EXPERIMENTS. It has long been recognized that the growing of alfalfa has a beneficial effect upon the producing capacity of irrigated lands; in other words, crops grown on land following alfalfa give larger yields than those following nonleguminous crops. In the series of experi- ments here reported it is aimed to show the extent of this beneficial effect as observed with three common field crops in several different rotations at three different locations in the northern Great Plains. These experiments were conducted by the Bureau of Plant Industry at the following places: (1) The Scottsbluff Field Station, 1 located on the North Platte Reclamation Project, near Mitchell, Nebr.; (2) the Belle Fourche Field Station, located on the Belle Fourche Reclamation Project, near Newell, S. Dak.; and (3) the Huntley Field Station, 2 located on the Huntley Reclamation Project, near Huntley, Mont. These stations are so situated as to be representa- tive of conditions on much of the irrigated land in the northern Great Plains, and it is believed that the results secured are generally applicable to that region. 3 1 The work of this field station is conducted and supported cooperatively by the United Btates Depart- ment of Agriculture and the Nebraska Agricultural Experiment Station. ' The work of this field station is conducted and supported cooperatively by the United Btates Depart- ment of Agriculture and the Montana Agricultural Experiment Station. 8 For a brief description of the agricultural and soil conditions of this region, see Scofield, C. S., Effect of farm manure in stimulating the yields of irrigated field crops. In Jour. Agr. Research, v. 15, No. 9, pp. 493-503. 1918. 185530°— 20— Bull. 881 2 BULLETIN 881, TJ. S. DEPARTMENT OF AGRICULTURE. --^/^ C~> DESCRIPTION OF THE EXPERIMENTS. These experiments are a part of an extensive series of rotations conducted under irrigation at the three stations specified. The experiments were started with the crop season of 1912 and have been continued without modification. The field plats, which include one- fourth of an acre each, are laid out in series. The series are separated by 40-foot roads, and the plats in the series are separated by 5-foot alleys. The plats at Scottsbluff are 132 feet long by 82.5 feet wide; those at Belle Fourche are 264 feet long by 41.25 feet wide, and those at Huntley are 227 feet long by 48 feet wide. The present bulletin deals with the effect produced by growing alfalfa for one, two, or three years on plats which are later used for two or three years for other crops and then are reseeded to alfalfa. The alfalfa crops are cut for hay, and at the end of the alfalfa period the land is plowed soon after the last cutting, so that only the stubble is plowed under. The results are based on seven pairs of rotations, the two members of each pair differing from each other only in that one member includes either two years or three years of alfalfa, while the other does not. Each rotation occupies as many plats as there are years in the cycle, so that each crop is represented each year. The crops and sequences involved in the 14 rotations are as follows: Rotation 20: Potatoes, sugar beets. Rotation 40: Alfalfa, alfalfa, potatoes, sugar beets. Rotation 22: Oats, sugar beets. Rotation 42: Alfalfa, alfalfa, oats, sugar beets. Rotation 24: Potatoes, oats. Rotation 44: Alfalfa, alfalfa, potatoes, oats. Rotation 28: Wheat, oats. Rotation 48: Alfalfa, alfalfa, wheat, oats. Rotation 30: Potatoes, oats, sugar beets. Rotation 60: Alfalfa, alfalfa, alfalfa, potatoes, oats, sugar beets. Rotation 31: Potatoes, oats, sugar beets (manured). Rotation 61: Alfalfa, alfalfa, alfalfa, potatoes, oats, sugar beets (manured). Rotation 32: Corn, oats, sugar beets. Rotation 62: Alfalfa, alfalfa, alfalfa, corn, oats, sugar beets. It will be noted from the list of rotations that the comparisons to determine the effect of the alfalfa are made between 2-year and 4-year rotations and between 3-year and 6-year rotations. In the first set of comparisons a 2-year period of alfalfa is used and in the second set a 3-year period. As these rotation experiments were started in 1912, in each case on land that had not previously grown alfalfa, there was no effect to be observed until 1913, and the crops grown that year following alfalfa were from plats that had been in alfalfa only one season. The first full effect of the alfalfa in the rotation was obtained in the 4-year rotations in 1914 and in the 6-year rotations in 1915, and then only in the case of crops which immediately succeed alf alf a in the rotation. EFFECT OF ALFALFA ON YIELDS OF FIELD CROPS. 3 In the above list of the seven rotations which include alfalfa, that crop was followed by potatoes in four cases and by oats, wheat, and corn in the other three. The second-year effect of alfalfa is shown in two cases on sugar beets and in five cases on oats. In the three 6-year rotations, sugar beets are grown the third year fol- lowing the alfalfa and presumably, therefore, derive the least benefit from that crop. The cultural operations used with these rotations have been only those demanded by good farming. With respect to any one crop, the same variety has been used in all rotations at each station each year. The same varieties have not been used at the different stations, nor has the same variety been used for all years at the same station. It has been the aim to use one of the best of the locally adapted varieties in each case. In the rotations where alfalfa follows sugar beets, the alfalfa has been seeded in the spring following the beet crop, and consequently it has done little more than get well established the first year. Where the alfalfa follows oats it has been customary to seed it in the fall in the oat stubble, and in general this has resulted in a good stand and nearly a full crop the following season. At the close of the alfalfa period in these rotations the alfalfa sod has been plowed immediately after the last cutting. This first plowing or "crowning," as it is called, is done only 3 or 4 inches deep, in order to cut the roots close to the surface and kill the plants. After the inverted sod has dried out well it is disked, and the land is then plowed to a depth of 8 or 9 inches. The field work of these rotation experiments has been under the direction of the farm superintendent at each station and under the immediate supervision of a scientific assistant, who is charged with performing or directing the cultural operations, the irrigation, and the harvesting, and with taking the field notes and reporting the results each year. 1 RESULTS OF THE EXPERIMENTS. IRISH POTATOES. There are four pairs of rotations at each station in which the mem- bers of the pairs differ from each other only in that one includes a period of alfalfa and the other does not. In two of these cases, 1 The following is the personnel concerned with the field work of these rotation experiments: At Scotts- bluff, Mr. Fritz Knorr wassuperintendentfroml910totheendofl916. Mr. JamesA. Holden was in charge of the irrigated rotations from the spring of 1912 until the end of 1910, when he succeeded Mr. Knorr as farm superintendent. Mr. David W. Jones supervised the irrigated rotation work during 1917 and the early part of 1918, when he entered the military service; during the remainder of the season Mr. Holden directed the work. At Belle Fourche, Mr. Beyer Aune has been superintendent since 1909. He has kept in close touch with the irrigated rotation work, being assisted at different times by Mr. John is. Wantz, Mr. X. L. Mattice, Mr. George T. Ratliffe, and Mr. Oscar Ii. Mathews. At Huntley Mr. Dan Hansen has been superintendent since 1910. The irrigated rotations were under the supervision of Mr. John M. Spain during 1912, Mr. John W. Knorr dining 1914, and Mr. Edward G.Noble from 1915 until the summer of 1918, when Mr. Xobleentered the military service. Mr. Hansen directed the work in 1913 and during the latter part of 1918. 4 BULLETIN" 881, U. S. DEPARTMENT OF AGRICULTURE. rotations 40 and 44, the alfalfa period covers two years and in rota- tions 60 and 61 it covers three years. In the above-enumerated rotations the 1913 potato crops followed only one year of alfalfa. In 1914 they followed two years of alfalfa, which is the normal course for the first two rotations, 40 and 44, while for rotations 60 and 61 the normal course of three years of alfalfa was first reached for the crop of 1915. Table I shows the yields of potatoes for the four pairs of rotations at each of the three stations. These yields, given in bushels per acre, are for the total crop, including small and diseased potatoes. The annual difference in yield between the crops following alfalfa and the check plats are also shown in the table, together with the mean annual yield of the crop for each rotation and the mean of the annual differences in yield. With each of the means the probable error is given. 1 The results given in Table I show that in nine cases out of twelve the mean of the annual differences in yield was in favor of the crops following alfalfa. But in only six of the nine cases is this mean difference significant; that is, more than three times the probable error. In the other six cases the mean is less than three times the probable error and is not regarded as significant. It has been customary in connection with these experiments to sort the potatoes in the field at the time of digging. This sorting has been done by means of a wire screen with 2-inch meshes. The smaller potatoes that pass through this screen are classed as un- marketable, while those passing over the screen are marketable. It has been observed that at Scottsbluff the percentage of marketable potatoes has been significantly larger from the plats following alfalfa than from the check plats. This has not been true, however, at Belle Fourche or at Huntley. It is clear from the facts set forth in Table I that the beneficial effect of alfalfa on subsequent yields of potatoes has been much more marked and consistent at Scottsbluff than at the other two stations. This may be due to the fact that the soil at Scottsbluff is a light sandy loam, while at both the other stations the soil is a heavy clay loam. The essential facts concerning these yields for each of the three sta- tions are summarized in the following paragraphs. At Scottsbluff the yield of potatoes, large and small, for the 48 plat years has averaged 236 bushels per acre, with a mean annual difference resulting from alfalfa of 100 ± 7. The yield of marketable 1 The probable error of the mean as used in these tables is obtained by Merriman's formula 36, which is A QA CO -j stated as follows: r o p=» ■ ' In other words, the probable error of the mean is obtained by multiply- nyra— 1 Ing the sum of the departure frsm the mean by the quotient oin-^n—l into 0.4853, where n equals the number of yields involved. (Merriman, Mansfield. Method of Least Squares, ed. 8, p. 223. New York, London, 1913.) EFFECT OF ALFALFA ON YIELDS OF FIELD CROPS. potatoes from the same plats excepting 1918, when this classification was not made, has averaged 192 bushels per acre, with a mean annual difference in favor of those following alfalfa of 101 ± 7. Again omitting the crop of 1918, the percentage of the total yield classed as marketable is 76, while the mean annual difference in percentage marketable in favor of those following alfalfa is 12 ±1.3. Table I. — Effect of alfalfa on the yields of Irish potatoes at the Scottsbhiff, Belle Fourche, and Huntley Field Stations, for the 6-year period from 1913 to 1918, inclusive. Station and rotation No. Yield of potatoes per acre (bushels). 1913 1914 1915 1916 1917 1918 Mean. Scottsbluff: 20 (no alfalfa) 398 403 146 280 88 206 142 285 131 273 87 179 165 ±29 271 + 20 Difference + 5 + 134 + 118 + 143 + 142 + 92 + 106+14 24 (no alfalfa) 235 402 146 319 109 228 217 308 134 290 150 -227 165+15 296+18 + 167 + 173 + 119 + 91 + 156 + 77 + 131 ±13 30 (no alfalfa) 329 322 216 272 146 231 226 319 167 281 79 238 194±24 60 (following alfalfa) 277±11 Difference - 7 + 56 + 85 + 93 + 114 + 159 + 83 + 15 31 (no alfalfa^ 353 380 243 299 175 220 244 306 211 346 81 249 218 + 23 300+17 Difference + 27 + 56 + 45 + 62 + 135 + 168 + 82±17 Belle Fourche: 20 (no alfalfa) 128 88 86 96 102 94 157 129 133 124 167 203 129+ 9 40 (following alfalfa) 122+11 Difference - 40 + 10 — 8 - 2S - 9 + 36 - 7+ 7 24 (no alfalfa) 109 177 112 127 111 144 151 149 120 170 191 153 132 ±10 44 (following alfalfa) 153± 5 Difference + 68 + 15 + 33 - 2 + 50 - 38 + 21+11 30 (no alfalfa) 74 97 68 105 59 105 166 119 139 108 168 170 112+17 60 (following alfalfa) 117+ 7 Difference + 23 + 37 + 46 - 47 - 31 + 2 + 5+11 31 (no alfalfa) 90 139 140 112 137 115 188 124 205 130 231 165 165 ±'16 61 (following alfalfa) 131+ 5 Difference + 49 - 28 - 22 - 64 - 75 - 66 - 34+13 Huntlev: 20 (no alfalfa) 200 250 179 156 350 350 228 247 241 224 390 415 265 ±20 40 (following alfalfa) 279 ±30 Difference + 50 - 23 + 19 - 17 + 55 + 14+10 24 (no alfalfa) 316 113 171 195 273 190 236 166 229 182 315 373 257±17 203 ±21 -203 + 24 - 83 -70 -47 + 58 - 54±25 30 (no alfalfa) 188 285 156 293 22S 397 224 292 175 23 S 286 345 209±14 60 (following alfalfa) 308± 16 Difference + 97 + 137 + 169 + 68 + 63 + 59 + 99 ±14 31 (no alfalfa) 160 277 140 184 273 420 212 in.' 91 2117 324 471 200 ±26 61 (following alfalfa) 343±34 Difference + 117 + 44 + 147 + 190 + 206 + 150 + 143+15.5 6 BULLETIN 881, IT. S. DEPARTMENT OF AGRICULTURE. At Belle Fourche the yield of potatoes, large and small, for the 48 plat years has averaged 135 bushels per acre, while the mean annual difference resulting from the growing of alfalfa has been a decrease of 4 ± 6. The yield of marketable potatoes from the same plats has averaged 107 bushels per acre, with a mean annual decrease for the plats following alfalfa of 4 ±5.6. The percentage of the total yield classed as marketable for the 48 plats is 81, with a mean annual difference in favor of the plats following alfalfa of 0.5 ±2.2. These results indicate that at Belle Fourche there has not been, so far, any beneficial effect from alfalfa on subsequent yields of potatoes. At Huntley the total yield of potatoes for the 48 plat years has averaged 258 bushels per acre, while the mean annual difference in favor of the plats following alfalfa is 50 ± 12.6. The yield of market- able potatoes from the same plats has averaged 241 bushels per acre, with a mean annual difference in favor of the plats following alfalfa of 55 ±11.4. The percentage of the total crop classed as marketable is 93, with the difference in favor of the plats following alfalfa of 1±0.55. Thus, the results from the Huntley station indicate that the beneficial effect of alfalfa on subsequent potato crops, though fairly large, is, when judged by the size of the probable error, barely significant. In an earlier paper, the effects of farm manure on the crop yields in certain of these irrigated rotations was reported, 1 and it seems proper to present here a comparison between the effects of periodical applications of farm manure and the use of alfalfa in the rotation. Such a comparison of results appears to be justified, because the two tests were made in the same fields and the same set of plats were used as checks in both cases. The experiments reported for the test of farm manure covered the 6-year period from 1912 to 1917, while those of alfalfa covered the 6-year period from 1913 to 1918. There were, however, only three rotation pairs for the potato ex- periments with manure, while there were four pairs with alfalfa. Also, in the manure experiments the manure was applied immedi- ately preceding the potato crop in two of the three cases and to the sugar-beet crop, which preceded the potatoes, in the third case. In the alfalfa experiments the potato crop followed the alfalfa in all four cases. The comparative features of the two experiments are summarized in Table II. The results brought together in Table II show clearly that on the lighter soil of the Scottsbluff station both manure and alfalfa have a beneficial effect on the yield of potatoes. The manure has resulted in an increased total yield of the treated plats over that of the check 1 Scofield, C. S. Loc. cit. EFFECT OF ALFALFA ON" YIELDS OF FIELD CROPS. plats of 40 bushels per acre, while the alfalfa has increased the yield by 100 bushels per acre over that of the check plats. At Belle Fourche and at Huntley the beneficial effects of manure have been at least significant. The alfalfa has not produced increased yields at Belle Fourche, though it has done so at Huntley. Table II. — Comparison of the effect of farm manure and of alfalfa on subsequent yields of Irish potatoes in crop rotations under irrigation at the Scottsbluff, Belle Fourche, and Huntley Field Stations. Factors compared. Yield of potatoes per acre. Scottsbluff. Manure. Alfalfa Belle Fourche. Manure. Alfalfa Huntley. Manure. Alfalfa Total crop: Yield (mean of check and treated plats) bushels. Mean annual difference do. . . Marketable potatoes: Yield do. . . Mean annual difference in yield. do. . . Percentage Mean annual difference in percentage. 208 40±7 150 40 ±7 72 8±1.5 236 100±7 192 101 ±7 76 12±1.3 131 34±6.4 105 36±6.3 7±1.9 135 -4±6 107 -4±5.6 81 .5±2.2 239 26±8.3 221 24±8.5 92 258 50±12.6 241 55±11.4 93 1±.55 OATS. The effect of alfalfa on the subsequent yield of oats is shown in Table III for six pairs of rotations at Scottsbluff and Belle Fourche and for four pairs at Huntley. The oats crop follows directly after alfalfa in only one rotation (No. 42) at each station. In all the other rotations the oats occur as the second crop after alfalfa, being preced- ed by potatoes in three cases (Nos. 44, 60, and 61), by wheat in one case (No. 48), and by corn. in one (No. 62). Because of this position in the rotation the oats did not come on plats that had been in alfalfa until 1914 except in the case of rotation No. 42. Thus, 16 compari- sons are made in Table III, of which 12 show increases in the mean yield of the crops following alfalfa and 4 show decreases. But if we accept as a test of significance of the mean that it shall be at least three times as large as its probable error, then only 5 of the 16 comparisons show definite benefits from the alfalfa, and in one case, (rotation No. 42, at Belle Fourche) there is a consistent reduction in yield following alfalfa. While these results do not show a strikingly beneficial effect from the use of alfalfa in the rotation, it is to be observed that these oat crops have been grown on soil that was virgin at the beginning of tho experiment and of relatively high productivity, as shown by the mean yields of all the plats included in the experiment. It has been noted also in connection with these experiments that the plant growth has been more vigorous on the plats of oats following alfalfa, as is shown in the yields of straw. These notes, together with the facts concerning the grain yields for each of the three stations, are summarized below. BULLETIN 881, U. S. DEPARTMENT OF AGRICULTURE. Table III. — Effect of alfalfa on the Huntley Field Stations during yields of oats at the Scottsbluff, Belle Fourche, and the 6-year period from 1913 to 1918, inclusive. Station and rotation No. Yield of oats per acre (bushels). 1913 1914 1915 1916 1917 1918 Means. Scottsbluff: 22 (no alfalfa) 90 101 76 95 16 16 49 55 75 79 53 71 60±8 70±8 + 11 + 19 + 6 + 4 + 18 + 10+2 24 (no alfalfa) 69 95 19 20 56 62 65 69 50 72 52±G 64±G + 26 + 1 + 6 + 4 + 22 + 12 + 4 28 (no alfalfa) 65 83 9 22 33 41 53 61 44 59 41 + 7 53 + 7 + 18 + 13 + 8 + 8 + 15 + 12±1.5 30 (no alfalfa) 79 84 16 18 64 56 65 74 69 77 59±7 62±S + 5 + 2 - 8 + 9 + 8 + 3±2 31 (no alfalfa) 86 83 20 19 71 56 88 76 80 90 69 + 8 65±9 - 3 - 1 - 15 - 12 + 10 - 4±3 32 (no alfalfa) 51 70 10 12 68 48 61 65 60 79 50±7 55±S + 19 + 2 - 20 + 4 + 19 + 5 + 5 Belle Fourche: 22 (no alfalfa) 45 26 77 61 99 75 57 36 71 35 87 48 73±6 47±5 - 19 - 16 - 24 - 21 - 36 - 39 -26 + 3 21 (no alfalfa) 74 110 112 116 58 58 73 72 90 83 81±7 88±9 + 36 + 4 - 1 - 7 + 7±5 28 (no alfalfa) 26 105 50 118 27 58 40 69 36 86 36±3 48 (following alfalfa) 2 years 87 + 7 + 79 + 68 + 31 + 29 + 50 + 51 + 7 30 (no alfalfa) 93 95 107 109 56 50 66 52 70 78 78+7 60 (following alfalfa) 2 years 77±9 + 2 + 2 - 6 - 14 + 8 — 1±3 31 (no alfalfa) 90 100 104 114 71 83 76 49 81 81 84±4 85 ±7 + 10 + 10 + 12 - 27 + 1±5 92 104 68 80 62 64 41 45 54 67 64 + 6 62 (following alfalfa) 2 years 72±7 Difference + 12 + 12 + 2 + 4 + 13 + 8±2 Huntley: 22 (ho alfalfa) 97 103 109 84 79 73 94 91 81 89 99 103 93±3 42 (following alfalfa) 1 year 90±3 Difference + 6 - 25 - 6 - 3 + 8 + 4 - 3±3 24 (no alfalfa) 103 105 81 77 72 83 68 62 93 93 83±5 44 (following alfalfa) 2 years 84±5 Difference + 2 - 4 + 11 - 6 + 1 + 2 30 (no alfalfa) 87 108 104 82 47 102 46 87 80 127 73 + 9 60 (following alfalfa) 2 years 101 ±6 Difference + 21 - 22 + 55 + 41 + 47 +28±10 31 (no alfalfa) 94 103 103 76 T 105 50 111 86 119 82±6 61 (following alfalfa) 2 years 103 ±4 Difference + 9 - 27 + 28 + 61 + 33 +21 ±10 EFFECT OF ALFALFA ON" YIELDS OF FIELD CROPS. 9 At Scottsbluff the yield of oats, grain, for the 62 plat years has averaged 58 bushels per acre, with a mean annual difference in favor of those following alfalfa of 6 ±1.3. The yield of straw from these same plats, omitting the crop of 1915, which was injured by hail and cut with a mower, has averaged 1.28 tons per acre, with a mean annual difference in favor of the plats following alfalfa of 0.30 ±0.05. Thus, while the yield of grain following alfalfa was increased by 10 per cent of the mean yield of all plats, the yield of straw was increased by 23 per cent. At Belle Fourche the yield of grain for the 62 plat years has aver- aged 72 bushels per acre, with a mean annual difference in favor of those following alfalfa of 5 ± 3 . The yield of straw from these same plats has averaged 1.24 tons per acre, with a mean annual difference in favor of the plats following alfalfa of 0.31 ±0.06. Thus, the yield of grain following alfalfa has been increased by 7 per cent, while the yield of straw has been increased 25 per cent. At Huntley the yield of grain for the 42 plat years has averaged 88 bushels per acre, with a mean annual difference in favor of the plats following alfalfa of 11 ±3.7. The yield of straw from these same plats has averaged 1.51 tons per acre, with a mean annual difference in favor of the plats following alfalfa of 0.55 ±0.05. Thus, while the increase in the yield of grain has been 12.5 per cent, the increase in the yield of straw has been 36 per cent. SUGAR BEETS. The effect of alfalfa on the yield of sugar beets is shown in Table IV. Five pairs of rotations are reported for Scottsbluff and Belle Fourche and four pairs for Huntley. Two of the rotations at each station cover four years, the sugar-beet crop of 1914 being the first to come on plats that had been in alfalfa. The normal course of the rotation was not in effect in these cases until 1915. In the other rotations the first alfalfa effect reached the beet crop only in 1915, and the full effect of three years of alfalfa was not obtained until the crop of 1917. Coming, as it does, in the second or third year after the alfalfa, the sugar-beet crop can not be expected to show the benefits of alfalfa in the rotation that are shown by the potatoes and oats. Yet in the 14 comparisons of mean yields shown in Table IV, 5 of the means show significant differences in favor of the alfalfa rotations; 1 shows a significant difference against alfalfa, and 8 show differences that are not significant. If we consider only the comparisons in which the full course of alfalfa has been in effect, i. e., the yields for 1917 and 1918 for the 6-year rotations, we have 40 annual comparisons, of which 24 show increased yields of 1 ton or more for the beets following alfalfa, while 8 show decreases of 1 ton or more, and 8 show differences of less than 1 ton per acre. 10 BULLETIN" 881, U. S. DEPARTMENT OF AGRICULTURE. Table IV. — Effect of alfalfa on the yields of sugar beets at the Scottsbluff, Belle Fourche; and Huntley Field Stations, 1914 to 1918, inclusive. Station and rotation No. Yield of sugar oeets per acre (tons). 1914 1915 1916 1917 1918 Means. Scottsbluff: 14.5 21.2 10.6 16.3 5.8 10.4 13.0 17.7 15.3 21.8 11.8+1.2 17.5 + 1.4 +6.7 + 5.7 +4.6 +4.7 + 6.5 + 5.7± .3 22 (no alfalfa) 14.2 20.7 12.0 16.3 7.3 7.3 11.1 14.5 14.3 21.9 11.8+ .7 16.1 + 1.8 +6.5 +4.3 + 3.4 + 7.6 +4.3+ .9 30 (no alfalfa) : 10.2 12.5 9.8 7.3 9.1 15.3 10.6 16.0 9.9± .2 12.8 + 1.4 +2.3 -2.5 +6.2 + 5.4 + 2.9±1.4 31 (no alfalfa) 15.6 15.3 17.1 11.9 16.0 19.5 20.2 23.3 17.2+ .7 17.5±1.9 -.3 -5.2 +3.5 +3.1 + .3+1.4 32 (no alfalfa) 10.1 13.3 8.8 6.8 10.8 15.4 8.9 16.5 9.6+ .4 62 (following alfalfa) 3d year 13. Oil. 5 +3.2 -2.0 +4.6 + 7.6 +3.4+1.3 Belle Fourche: 20 (no alfalfa) . 11.3 12.8 12.2 11.0 9.7 8.8 15.3 14.1 10.9 11.0 11.9+ .6 40 (following alfalfa) 2d year 11.5+ .6 +1.5 -1.2 -.9 -1.2 + .1 — .4+ .4 22 (no alfalfa) 12.3 11.1 9.1 7.0 8.1 4.2 12.7 10.0 8.6 8.9 10.2+ .8 8.2± .9 -1.2 -2.1 -3.9 -2.7 + .3 -2.0+ .5 30 (no alfalfa) . 7.3 9.4 4.6 7.2 7.4 12.7 7.3 13.7 6.6+ .5 10.7+1.2 +2.1 +2.6 + 5.3 +6.4 12.2 13.8 +4.1+ .9 31 (no alfalfa) 13.2 10.9 8.2 10.4 15.3 15.7 12.2 + 1.0 12.7+1.0 -2.3 +2.2 + .4 + 1.6 + .5+ .7 32 (no alfalfa) . . *. '. 6.8 8.3 4.0 4.8 7.6 8.5 6.0 9.9 6.1+ .7 62 (following alfalfa) 3d year 7.9+ .7 + 1.5 + .8 + .9 +3.9 + 1.8+ .5 Huntley: 20 (no alfalfa) 15.1 13.9 8.3 15.4 15.3 10.4 9.6 8.4 14.6 16.2 12.6 + 1.2 12.9+1.2 -1.2 +7.1 -4.9 -1.2 + 1.6 + .3 + 1.4 22 (no alfalfa) 10.4 9.3 6.8 7.6 11.1 11.4 11.3 5.9 10.2 13.1 10.0+ .5 9.5+ .9 -1.1 + .8 + .3 -5.4 +2.9 -.5+ .9 30 (no alfalfa) 4.8 12.9 6.7 7.4 6.7 8.3 8.4 14.2 6.7+ .4 10.7+1.6 +8.1 + .7 + 1.6 + 5.8 +4.0+1.4 31 (no alfalfa) 9.1 8.7 10.0 15.6 9.6 13.0 10.6 14.7 9.8+ .2 13.0+1.0 -.4 + 5.6 +3.4 +4.1 +3.2+ .9 In addition to recording the yield of beets from these rotation plats, it has been customary also to determine the average size of the beets by counting and weighing the product of several represent- EFFECT OF ALFALFA ON YIELDS OF FIELD CROPS. 11 ative rows, to record the percentage of sugar in the beets as reported by the local sugar factory upon the samples from each plat, and to determine the proportion of the weight of the tops to the combined weight of beets and tops. This last determination is important not only as showing something of the vigor of growth of the sugar beets, but also as indicating the quantity of feed available as a by-product of the beet crop. The facts for each of the three stations regarding the effect of alfalfa in stimulating the yield of subsequent crops of sugar beets, as shown in Table IV, and also as to its effect on the size of beets, the percentage of sugar in the beets, and the percentage of tops are sum- marized below. At Scottsbluff the yield of beets from the 44 plat years averaged 13.8 tons per acre, while the mean annual difference in favor of those following alfalfa (second and third year) was 3.4 ±0.5. The size of beets from the same plats averaged 1.53 pounds, with a mean annual difference in favor of those following alfalfa of 0.39 ±0.032. The sugar content of the beets for the 44 plat years averaged 17 per cent, with a mean annual difference against the plats following alfalfa of 0.5 ±0.15. The proportion of the weight of tops to the combined weight of beets and tops for the 44 plat years is 27 per cent, with a mean annual difference in favor of the beets following alfalfa of 2.3 ±0.6. At Belle Fourche the yield of beets for the 44 plat years averaged 9.9 tons per acre, with a mean annual difference in favor of the plats following alfalfa (second and .third year) of 0.64 ±0.36. The size of the beets from the same plats averaged 0.78 pound, with a mean annual difference in favor of the plats following alfalfa of 0.08 ±0.035. The percentage of sugar in the beets averaged 19.7 per cent, while the mean annual difference in favor of the plats following alfalfa is 0.5 ±0.19. The records as to percentage of tops are incomplete. At Huntley the yield of beets for, the 36 plat years averaged 10.7 tons per acre, with a mean annual difference in favor of the plats following alfalfa of 1.5 ±0.6. The size of beets from the same plats averaged 0.96 pounds, with a mean annual difference in favor of those following alfalfa of 0.1 7 ±0.05. The sugar in the beets averaged 17 per cent, with a mean annual difference against the plats following alfalfa of 1.3 ±0.22. The proportion of the weight of tops to the combined weight of beets and tops, omitting 1918, when the records were not made, has averaged 38 per cent, with a mean annual dif- ference in favor of the plats following alfalfa of 8 ±1.8. It is possible to make a comparison between the effect of alfalfa on the subsequent yield of beets and the effect of the application of farm manure at the rate of 12 tons per acre, as was done with the potato crop. The chief difference in the two comparisons is that 12 BULLETIN 881, U. S. DEPARTMENT- OF AGKICULTURE. where manure was used it was applied directly preceding the beet crop in three of the four cases, while in the alfalfa rotations one or two other crops occur between the alfalfa and the beet crops. There were four rotation pairs in the manure experiments previously de- scribed, 1 covering a 6-year period, 1912 to 1917. A summary of those results, together with the results given in the preceding para- graphs, is presented in Table V. These comparisons show that the period of alfalfa in the rotation has been nearly as beneficial as the periodical applications of farm manure, even though the position of the beet crop in the alfalfa rotations has not been so favorable as in the manured rotations. It is also to be remarked that while both manure and alfalfa have increased the yield of the beets, the size of beets, and the vigor of growth, as expressed in the larger proportion of tops, there has not been a corresponding increase in the per- centage of sugar in the beets. Table V. — Comparison of the effect of farm manure and of alfalfa on subsequent yields of sugar beets in irrigated-crop rotations at the Scottsbluff, Belle Fourche, and Huntley Field Stations. Factors compared. Mean yields per acre. Scottsbluff. Manure. Alfalfa Belle Fourche. Manure. Alfalfa Huntley. Manure. Alfalfa Yield of treated and untreated plats tons. Annual difference do... Size of beets pounds. Annual difference in size. do. . . Sugar in beets per cent . Annual difference do... Yield of tops do... Annual difference 15.3 +4.3±.28 1.55 + .32±.044 16.5 -. 12±.20 26 + 2.7±.6 13.8 +3.4±.5 1.53 + .39±.032 17.0 + .5±.15 27 +2.3±.6 10.7 + 1.9±.36 .84 +.08±.035 19.6 4- .3±.22 9.9 +.64±!36 .78 +.08±.035 19.7 + .5±.19 11.3 +2.6±.33 . 92 + .21±!o34 16.8 +.16±.17 32 + 3.2±1.12 10.7 + 1.5±.6 .96 + .17±.05 17.0 -1.3±.22 38 + 8. Oil. 8 SUMMARY. The effect of a period of two or three years of alfalfa in a rotation on the subsequent yields of Irish potatoes, oats, and sugar beets grown under irrigation has been tested for six years at three different stations in the northern Great Plains. Comparison is made between the yields of these crops when grown in the same sequence but with- out alfalfa. A further comparison is made in the case of potatoes and sugar beets as to the relative effect of a period of alfalfa in the rotation and the application of farm manure at the rate of 12 tons per acre once during the period of the rotation. At Scottsbluff, Nebr., where the soil is light sandy loam, the effect of alfalfa has been to increase the yield of potatoes about 100 bushels per acre, to increase the proportion of marketable potatoes about 12 per cent, to increase the yield of oats about 6 bushels per acre, and to increase the yield of sugar beets 3.4 tons per acre. i Scofield, C S. Loc. cit. EFFECT OF ALFALFA ON YIELDS OF FIELD CROPS. 13 At Belle Fourche, S. Dak., where the soil is heavy clay loam rich in organic matter, there has been no beneficial effect from alfalfa on the subsequent potato crop, and the effect on oats and sugar beets, while apparently beneficial, has been too slight to be regarded as significant. At Huntley, Mont., on a very productive clay-loam soil, the effect of alfalfa has been to increase the yield of potatoes about 50 bushels per acre, without, however, increasing the proportion of marketable potatoes, which has been relatively high on all plats. The alfalfa has apparently increased the yield of oats about 1 1 bushels per acre and the yield of sugar beets about 1.5 tons per acre. A comparison of the results from the use of alfalfa in the rotation with those from the use of farm manure shows that with potatoes at Scottsbluff the alfalfa is distinctly more beneficial than farm manure, although the latter gives excellent returns. With the other crops and at the other stations the differences between the effects are less striking, and in general the farm manure has given better results. WASHINGTON : GOVERNMENT PRINTING okeige : 1920 LIBRARY OF CONGRESS niiiiii mi mil in uii 021 490 129 8