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CaBege at Agricultural !deneel

SOiybean, _.....__"".J,.,.,Fa€:ts

Defldent soybean stands. force farmers to considerreplanting. In many cases, reptantlng Is,the wrongdedston, Farmers often underestimate the yieldpotential of' a,deffdent stand: Soybeans have a .tremendous: ability to compensate for row populatfonsor gaps fill rows, M,tlillittle or no loss ofi yteld. ~

RepJ:antlng wHi!not, necessarily resulitlfa yieldshlghell than those produced- by a deft dent stand

..--.., becauseos the yield~penalty for delayecl plantinginherent toreprantfnm

The proper replant decision can. be reached byfollowing it series o~,sreps whldJ; are outHned below.First, the defidel'ltJ stand must be evaluated todetermine' the popullaUon ilnd distribution of therem·afinr'lg pFanb. Second* the potential yield of arepEanted stand ES:estiMated. Finally, the dedslon torepfant 01 naG fiS!made Oft the oasIs of economics.Although ill repa:anted! stand ma~ ot:l:tyfefd the ongfnaldeffdentl'stand!, replanting ma,)" not result fn aneconomic gain because-ofithe adtlJtfonaV seed, fuel,and'somenmes nerbtcide costs.inherent to repfan,Ung.Replantfng;wfWnot' necessarily result In' an adequatestand: If the farmer is nottotally convmces tha,'replanting would' be economically acfvantag~olJts" theOriginal stand'should.be kept

To evaluate possible dettctent stands; growersmouJ'd refer toEvaluating DeficientSoybean Stan:th,Soybean Facts SF-6~

The yield potentfa:l1 of at defict'ent standi can, bepredfcted by the use of Taoll" 11,wnrc1il,was cfr.a:wnfromthe nUno!S Agrono:my pf'cl'llld'oooi (A:nOD." 1986).Although Table 1 was devel10pecfhom researdJconducted In nUnois, IImtted researdJ fn Del'awanrIndIcates that nble 1 will also accurately predIct the

yield potential of deficient sl'ngle-crop~tJ soybeanstands hi); Delawar,e~ Table 1\ predicts, yield potential onthe basis 06 theper,centage of the stamd!lost to gaps Inrow" remaining, pl'ants peli foot of row, and 30-Inchrow widths. Plants pel foot 06 row must be adJustedfOI row wldtns othel tfialil! 30i Inches. FOil exem pie, theCO'UBlr.1lunder 6·plants pel! foot of row wou£d be usedto predfct the yield! potentialt of a stand wI"l plantspel foot 0'· row IAt liS-inch; row widths OF l!- h. pliant!per foot o. raw in 7-IndJ, row widths.

*'l;': .~nrcln.1!~ .•.IOOo6t(.•.~~~t~t_.,~t•• m~qq, r ttt." •• '!'*·I', ••.• ,I•••n·.~Tabw 1. Yield ~sponse of singl~4:fopeed soybeans in 30-

inch row spcudns to defidenti stQnds.

CJfJ stand lost Ifona,,"n, p&nb per foot of row

.!!1.!!f:!.. :__-==!.======:==!.===::==--:'====-~ fUlli yield potential--

o 100 n "10 98 9'6 9320 9'6 93 9130 9'3 90 8846 . 89 86 83SO 84 81 78

'60 7& 7S 73Source! Untv~rsFry of IHtnois

Exampfe. If 30C16of the stand was lost to gaps andthe remafni<01 roW secUons had 6 plants per foot ofrow, the stan'd can be expected to produce 90% o,f theyfeJict01 a\perie¢t stand. ]I the predIcted yleJd goal is 40but" afarme. can expect a yield 01 36 (90% of 40)flul AWith thr deffdenl stand.

Most deRdenf standJ contain gaps. OccasionallyunEform. but thin stands are produ(:ed. When gaps are

jACooperatiYe Extension Educadon it AlriQA"'- .-Id Home Economic:s. UrWtnity of Oelawn. Dele • .,. State College and If!WtUrii1ed States'Oepll1m8nt of AgricUlIJnt coopeta~. Ridlard ~ Fowtet. Oirec:tor. Distributed" kJrth&r8nce of Acts 01 Congress of Match 8 and June :30,101•. 11is 1M pcIicy of Iht 0e4aw.,. Coo~ EJtension SVStel'ft lhet no person st-.'>i\ 0. subjee1ed to cbcrimination on Ihe grounds 01

not present, sfngJe.aopped soybeans. can tolerate veryJow plmt populatlons bc:fQ~ ~gfif(~(·.linY(,ldreductfons result. Farmers should' nee consfderreplanting uniform, thin stands unless the pllntpopulation Is less than 35,000 plants. pel acre,provided, that weed' control and, soHirnolsture areadequate. Rarely will replanted soybeansoutyteld atimely planted; thin, uniform stand,

Yield prediction of replanted; soybeans. The yieldpotential for replanted soybeans can be obtained fromFIgure h r

Economic analysts, TIle yield>potential for thedefIdent stand should. be converted Into I dollar valueby multiplying. yield' potential! (as a fraction) by theexpected yield of a fuU stan.d and the price of a bushel

,__ ()!.~,qybear:!~.__ .__Examplea. Yield pctennat of defident stand. 70%b. Expected yf:efd of a fu~l stand. 40ibu/ Ac. Price of a bushel of soybeans. SS.SOd. Value of malntatnlngstand'. 0.7 x 40 x SS.50

:or Sl54! •

The same procedure would' then be done to obtai," adoHas vaJIue fOI replanted-beans. Only after addJUol'la·Fproducttors costs (fuel', seed, herblddes) are subtractedfrom the doltar valueofreplanted soybeans should areplanting decision be made. .

Replanting Double-Cropped SoybeansLess Information Is available on the effect of

defident stands-en double-crspped soybean yields,Double-croppedsoybeans are more affected! byplanting, date andplant population than sfngJ1e·cropped soybeans. pcubie-croppec soybeans rec uirehigher populations for optimum yields. tJIlar:t>slir;. gle-cropped' soybeans; A deffdent stand'wtll'reducedouble-cropped yields to a greater extent than slngte-cropped yields. However, the yteldpenatry assocrareewith replanting will also be greater for double-cropped:soybeans,

Based' on limited' data', Table 1 will overestimate theyield potential of a defldent stand of double-croppedsor.beans by about, 15%. To predict the yield potential!of a deffden1 stand' of double-cropped'soybeaas,choose the appropriate value from. Table l' andlmultiply by 0.85. FOl! example, ,ii double-croppec stand'(lS-lnch row width) reducecfby' 30% togapswitJfr.4remaining plants per foot of row would be expected toyield 79% (93 x 0.85) of a fuU stand.

. •• I , II

100

90

5/1f 6/1$ 1i/2il 7/' J 7/27"lclntinQ Oct.

t,;._.- ••- •.••..-_.-_' ••-' ••••-,..- •••-..._ •••••••.-- ••••- •••- .•••- ••••- ••• -••• -='••••..••••..••••••_ .•••••..••••••••• ..---- ... - .

Authors:B. L. Vasilu, Associate Professal', SOU and! Crop

Man8g,:mentR. W. Tayror, ExtensionSpecialut, AgronomyR. Unlatowsk1>, ~telUion Associate, Field! Crops

Notes,.,--.

SF· '-3191

Com1nereial'c:ompaniel Of products are mentioned in •• publicatian solely lor !he purpoM 01 pr:oYiding'speciflC inlormalion. MenDon or • company orpI'Oduct doe. not conatiMII • guatan •• Of watT'Wlty 01 ~ by tie Agricu,,", E.lperirMnt Swan Of DelawareCoo~ Extensionor antndOtMmtnI 0Yef' produeU ot olher c:omp.nin noe rneneoned.

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nodules. The bacteria \,vtthin tnese nod\.!;!~fix ~\l-2 ir.~inth~ r1tmosJ~thereana rnake itavailable to the iegl;z~me.The legl1me conh~1?::;teS to ~he ·{~'~far.e~f tMeb~delitt by p'tdvidlngthem with carbchydrates which tney use i~·-aii1dn1trgy source .~\fix fhe N·.THe quantity of

.N,which may be, fixed by Rhizobium are estimated; to, be between a,few pounds in somecases to over 500; Ibs/acre/year. This uppea value was encountered in optimal conditionsin some clover/qrassland systems in New Zealancf,. Under our conditions; the quantity ofN,fixed by most leg!uminous; crops is probably less than 1-50, Ibs/acre/year.

From an aqronornic point or' view, it is very. important to take into account OF credit,a certain amount of resldua] N! left in: the soil; from ell previous leg,ume crop (Table 3-6).Farmers can economize on Nl fertilizer costs ano also reduce' the potential for N03-

contamination ofsurface and groundwater resources, ..

Non-symbiotic N fixation is carriedi out by' free-I:ivi,ngbacteria! and: bl!ue-greem,algaein the soik The amount of N- fixed by these organisms is much less than the amount fixedsymbiotically. Some estimates onthe Nfixed by these orqanisms range from 20 to 45 IbIA,but a generally accepted' fig.ure is about 5 Ib/A. From an agrorlomic standpoint, thesesources of Nl are not very sig,nificant.

Table 3-6,. Residual nitrogen provided by legumes.

legumeTime passed anddensity of regume

Residualnitrogen(Ib/acre)

Alfalfa First year after alfalfa50%-75% standi25%-49% stand0%-25% standSecondi year after alfalfa50%-75%, sta'J11dFirst' yearr afte'Fclover or.trefoil25%-75-% standiFirst yeas afte,/!'soybeans fOI grain

4025

1108040

50Red cloverand trefoil'Soybeans

Source: PSU, 1990.

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