Dry peas grown as a cash crop in southern Idaho
are usually harvested by the first of August, which
leaves the land bare and unproductive for the last
third of the growing season, unless the
peas
were
used as a nurse crop to establish alfalfa. This raises
the question: Could August, September and the
early part of October be utilized for forage production
from plants other than alfalfa

Cary, J.W.

USDA - ARS - NWISRL

Idaho FallsD.gre. 5130Days25October9 1 . 23	 6 13 202 4 11 18228NUMBER 167	CURRENT INFORMATION SERIES 	 JUNE 1971DOUBLE CROPPING DRY PEASAND FORAGE IN SOUTHERN IDAHOJ. W. CaryDry peas grown as a cash crop in southern Idahoare usually harvested by the first of August, whichleaves the land bare and unproductive for the lastthird of the growing season, unless the This wereused as a nurse crop to establish alfalfa. rh'Is raisesthe question: Could August, September and theearly part of October be utilized for forage produc-tion from plants other than alfalfa?The quality of this part of the growing season isshown in Figure 1. The three solid curves give theaverage degree days with a base 50°F, for threelocations in southern Idaho, (a day with averagetemperature of 57°F would be counted as 7 degreedays, since the average was 7 0 above the 50 0 Fbase). The two dashed curves show the degee-daysat Twin Falls in 1969 and 1970.Although the development of plants depends onmany factors, such as weed management, soil mois-ture, soil fertility, day length and temperature ex-tremes, most plants must have maximum tempera-tures above 50 °F to make significant growth. Thus,with other factors ual, the larger the number ofdegree days during the growing period, the greaterthe potential production.Of course, the number of degree days in the fallis of little value for plant growth if the plants havebeen severely damaged by frost. The two marks oneach of the solid curves indicate theted datefor fall frost. The first mark indicates theexpec date, inone year out of ten, by which a 28°F minimum airtemperature will have occurred. The second markindicates the date with a 50-50 chance of the 28°Flow having occurred.Most frost-senstive plants, such as corn, sorghumand potatoes, will be severely damaged when airtemperatures fall to 28°F or below. More tolerantplants, such as grain, alfalfa, peas and beets, willcontinue to grow during the warmer part of the day,even though light frost occurs at night.By the end of October, the night temperaturesacross southern Idaho dip into the low 20's, which,combined with the short, cool days, essentially haltsthe growth of even the more hardy plants.FIELD TESTSTo demonstrate the forage production potentialof the last third of the Twin Falls. Following the har-vest of a pea field in 1969, three hybrid crops —corn, sorghum, and Sudangrass — were planted andirrigated up to the first week in August. As shown inFig. 1, the 1969 season was warmer than average;killing frost did not occur until October 3. Forageproduction from the Sudangrass and sorghum wasdisappointing; however, the corn in the best por-tions of the field with a population of 40,000 plantsper acre produced nearly 3 tons of dry matter peracre.Based upon these preliminary results, a secondstudy was initiated during the 1970 growing season.The experimental site was fertilized with phos-phorus in the fall of 1969. On March 25, 1970, one pintper acre of treflan was disked into the soil and thefield was subdivided to accommodate six differenttreatments, each replicated three times (Table 1).Four of the treatments were planted to peas,one to peas and 20 pounds of alfalfa per acre, andone to peas and approximately one pound of turnipsper acre. All peas were planted at 190 pounds peracre with a grain drill, using an alfalfa attachmentfor the alfalfa and turnip seeds. The field was thencorrugated on 24-inch centers.A good stand resulted, and the entire area wasuniformly irrigated according to the best availablerecommendations for dry pea production. At the endof July, the field was cut with a swather and thepeas harvested with a combine.The yield of dry peas averaged 28.6 sacks peracre from the pure stand of peas, 28.2 sacks peracre from the pea and alfalfa mix, and 24.5 sacksfrom the pea and turnips mix. Pea yields of 28 to 30sacks per acre for the 1970 growing season in theTwin Falls area were considered acceptable, sincethe weather conditions were not particularly favor-able for dry pea production and a -hail store near theend of July shelled out about a sack per acre.Figure 1. The degree days. base 50° F. for three locationsin southern Idaho (solid lines) and for individualperiods in 1989 and 1970 (dashed lines) near TwinFalls. The average number of degree days for thewhole growing season in the Twin Falls area isaround 2,200.11000	96750CaldwellTwin FaitsCOOPERATIVE EXTENSION SERVICE	 AGRICULTURAL EXPERIMENT STATIONCOLLEGE OF AGRICULTURE	 UNIVERSITY OF IDAHOTable 1. Yields and nitrogen status of forage crops. Plant-ing was done August 1. with the exception ofalfalfa and the first group of turnips, which wereHarvest	WetCrop	date	 weightCorn + peasAlfalfaWheat + peasSecond crop peasTurnips (March)Turnips (August)In addition to the information on yields and nitrogenanalyses shown in Table 1, the following items shouldbe noted:(a) The peas were all volunteer from seed left onthe surface after combining. Peas germinatedand grew well with the wheat and corn, but didnot appear in the turnips or alfalfa. The averageyield for second-crop peas came from three bor-der areas with the thickest volunteer stands,thicker even than one would plant for dry peaproduction.(b) Yields were measured on an oven-dried basis,which are lower than field-dried values. For ex-ample, the field-dried yield of alfalfa was 1.9tons per acre, while the oven-dried yield was1.5 tons.On August 1, 60 pounds per acre of nitrogen wereapplied to the field, and the four bare plot areaswere disked and planted to the forage crops shownin Table 1. The crops were planted with a graindrill and alfalfa attachment. The residual alfalfaand turnips on the two remaining plot areas werenot disturbed. The field was furrow irrigated twicein August and once in September.CONCLUSIONSThe results in the table and the climatic datain the figure show some potential for forage produc-tion from cool season plants following the harvestof dqwreas. The area of most promise extends fromthe Twin Falls region on west to the Oregon border.Lower second-crop yields can be expected to theeast of Twin Falls because of the rapidly decreasinglength of growing season.Alfalfa seeded with peas is already utilized fordouble cropping. Although alfalfa did not reduce theyield of dry peas during the 1970 season, successof the operation depends upon removal of the peacrop before the alfalfa makes significant regrowthin the early part of August. Turnips should not beplanted with peas, as they reduce dry pea yields.If pea fields are to be planted to a forage cropafter the pea harvest, then cool season plants suchas peas, a pea and grain mix, or turnips may be con-sidered.Corn and related plant species are not the bestchoices to follow peas because of the possibility offrost and cool weather in September. However, cornplanted to produce stands of 40,000 to 60,000 plantsper acre might be considered for fields on whichseeded with pees in March. Yields are averagesfrom three plots and include both tops and rootsin the case of turnips.Oven	Nitrogendried	Total	inweight	Nitrate	 nitrogen	forage(c) The turnips were all infested with maggots. Thoseplanted with peas in March lost most of theirtops to aphids in September. Those planted inAugust generally had healthy tops at harvest,but the largest roots were only 1 or 2 inches indiameter, even though they were planted at thelow rate of about 1 pound per acre.(d) The corn was planted to give 60.000 plants peracre. Hybrid seed was not used because of itsgreater cost, and because there would not betime for ears to form. The plants were between2 and 3 feet tall at the end of the growing season.The lower yield in 1970, compared to the maxi-mum of 3 tons produced in 1969, was primarilya result of fewer degree-days and cold tempera-tures that ended most of the corn's growth bySeptember 14 (Fig. 1).crop failure occurred in June or early July as aresult of an unseasonable freeze or a severe hail-storm.RECOMMENDATIONSAs the yields reported in Table 1 are for a singlegrowing season, and since no feeding trials wereconducted, specific recommendations would bepremature. However, the results indicate the poten-tial production of forage following peas in southernIdaho. If any of the crops would be useful in yourfarm or ranch operation, try them on a limited basisthe first year to gain some management experiencein growing the crops and in feeding the resultingforage.(For additional information on feeding the for-ages shown in Table 1, see Feeds and Feeding, byF. B. Morrison, Morrison Publishing Co., Ithaca,N. Y., 1954.)ABOUT THE AUTHOR: 3. W. Cary is research sail scien-tist at the Snake River Conservation Research Center,Northwest Branch, Soil and Water Conservation ResearchDivision, tura] Research Service, U.S. Depart-ment ofPublished and Distributed in Furtherance of the Acts of May 8 and June 30, 1514,by the University of Idaho Agricultural Extension Service, James E. Kraus.Director; and the U.S. Department of Agriculture, Cooperating.James E. Kraus, Director	 3M-841- tons/acre - lbs./acre9/18 6.1 1.1 0.30 2.5 4010/13 6.4 1.6 .25 2.3 8910/13 6.1 1.2 .18 2.7 8510/19 7.9 1.7 .34 2.9 9810/20 13.9 2.3 .13 1.5 8910/20 14.7 2.7 .20 1.7 92

Double Cropping Dry Peas and Forage in Southern Idaho

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Double Cropping Dry Peas and Forage in Southern Idaho

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