University of Delaware Soybean Replant Guide.

1. CaBege at Agricultural !deneel
SOiybean, _.....__"".J,.,.,
Fa€:ts
Defldent soybean stands. force farmers to consider
replanting. In many cases, reptantlng Is,the wrong
dedston, Farmers often underestimate the yield
potential of' a,deffdent stand: Soybeans have a .
tremendous: ability to compensate for row populatfons
or gaps fill rows, M,tlillittle or no loss ofiyteld. ~
RepJ:antlng wHi!not, necessarily resulitlfa yields
hlghell than those produced- by a deft dent stand
..--.., becauseos the yield~penalty for delayecl planting
inherent toreprantfnm
The proper replant decision can. be reached by
following it series o~,sreps whldJ; are outHned below.
First, the defidel'ltJ stand must be evaluated to
determine' the popullaUon ilnd distribution of the
rem·afinr'lg pFanb. Second* the potential yield of a
repEanted stand ES:estiMated. Finally, the dedslon to
repfant 01 naG fiS!made Oft the oasIs of economics.
Although ill repa:anted! stand ma~ ot:l:tyfefdthe ongfnal
deffdentl'stand!, replanting ma,)"not result fn an
economic gain because-ofithe adtlJtfonaV seed, fuel,
and'somenmes nerbtcide costs.inherent to repfan,Ung.
Replantfng;wfWnot' necessarily result In' an adequate
stand: If the farmer is nottotally convmces tha,'
replanting would' be economically acfvantag~olJts" the
Original stand'should.be kept
To evaluate possible dettctent stands; growers
mouJ'd refer toEvaluating DeficientSoybean Stan:th,
Soybean Facts SF-6~
The yield potentfa:l1 of at defict'ent standi can, be
predfcted by the use of Taoll" 11,wnrc1il,was cfr.a:wnfrom
the nUno!S Agrono:my pf'cl'llld'oooi (A:nOD." 1986).
Although Table 1 was devel10pecfhom researdJ
conducted In nUnois, IImtted researdJ fn Del'awanr
IndIcates that nble 1 will also accurately predIct the
yield potential of deficient sl'ngle-crop~tJ soybean
stands hi); Delawar,e~ Table 1 predicts, yield potential on
the basis 06 theper,centage of the stamd!lost to gaps In
row" remaining, pl'ants peli foot of row, and 30-Inch
row widths. Plants pel foot 06 row must be adJusted
fOI row wldtns othel tfialil! 30i Inches. FOil exem pie, the
CO'UBlr.1lunder 6·plants pel! foot of row wou£d be used
to predfct the yield! potentialt of a stand wI"l plants
pel foot 0'· row IAt liS-inch; row widths OFl!- 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 93
20 9'6 93 91
30 9'3 90 88
46 . 89 86 83
SO 84 81 78
'60 7& 7S 73
Source! Untv~rsFry of IHtnois
Exampfe. If 30C16of the stand was lost to gaps and
the remafni<01 roW secUons had 6 plants per foot of
row, the stan'd can be expected to produce 90% o,fthe
yfeJict01aperie¢t stand. ]I the predIcted yleJd goal is 40
but" afarme. can expect a yield 01 36 (90% of 40)
flulAWith thr deffdenl stand.
Most deRdenf standJ contain gaps. Occasionally
unEform. but thin stands are produ(:ed. When gaps are
jA
CooperatiYe 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

2. not present, sfngJe.aopped soybeans. can tolerate very
Jow plmt populatlons bc:fQ~ ~gfif(~(·.linY(,ld
reductfons result. Farmers should' nee consfder
replanting uniform, thin stands unless the pllnt
population Is less than 35,000 plants. pel acre,
provided, that weed' control and, soHirnolsture are
adequate. Rarely will replanted soybeansoutyteld a
timely planted; thin, uniform stand,
Yield prediction of replanted; soybeans. The yield
potential for replanted soybeans can be obtained from
FIgure h r
Economic analysts, TIle yield>potential for the
defIdent stand should. be converted Into I dollar value
by multiplying. yield' potential! (as a fraction) by the
expected yield of a fuU stan.d and the price of a bushel
,__ ()!.~,qybear:!~.__ .__
Example
a. Yield pctennat of defident stand. 70%
b. Expected yf:efd of a fu~l stand. 40ibu/ A
c. Price of a bushel of soybeans. SS.SO
d. Value of malntatnlngstand'. 0.7 x 40 x SS.50
:or Sl54! •
The same procedure would' then be done to obtai," a
doHas vaJIue fOI replanted-beans. Only after addJUol'la·F
producttors costs (fuel', seed, herblddes) are subtracted
from the doltar valueofreplanted soybeans should a
replanting decision be made. .
Replanting Double-Cropped Soybeans
Less Information Is available on the effect of
defident stands-en double-crspped soybean yields,
Double-croppedsoybeans are more affected! by
planting, date andplant population than sfngJ1e·
cropped soybeans. pcubie-croppec soybeans rec uire
higher populations for optimum yields. tJIlar:t>slir;. gle-
cropped' soybeans; A deffdent stand'wtll'reduce
double-cropped yields to a greater extent than slngte-
cropped yields. However, the yteldpenatry assocraree
with replanting will also be greater for double-cropped:
soybeans,
Based' on limited' data', Table 1 will overestimate the
yield potential of a defldent stand of double-cropped
sor.beans by about, 15%. To predict the yield potential!
of a deffden1 stand' of double-cropped'soybeaas,
choose the appropriate value from. Table l' andl
multiply by 0.85. FOl! example, ,ii double-croppec stand'
(lS-lnch row width) reducecfby' 30% togapswitJfr.4
remaining plants per foot of row would be expected to
yield 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,:ment
R. W. Tayror, ExtensionSpecialut, Agronomy
R. 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 or
pI'Oduct doe. not conatiMII • guatan •• Of watT'Wlty 01 ~ by tie Agricu,,", E.lperirMnt Swan Of DelawareCoo~ Extensionor an
tndOtMmtnI 0Yef' produeU ot olher c:omp.nin noe rneneoned.

3. ~
(1;
4.
J'l,;{ ...,
",, .,
)'
.£j
,."t.ll
~
.
';~.':'jj" ..
~
t.··,
••
'·11
••••
'~JI
~.;,..•1":
•
J
J
I
I
nodules. The bacteria ,vtthin tnese nod.!;!~fix ~l-2 ir.~inth~ r1tmosJ~thereana rnake it
available to the iegl;z~me.The legl1me conh~1?::;teS to ~he·{~'~far.e~f tMeb~delitt by p'tdvidlng
them 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 some
cases to over 500; Ibs/acre/year. This uppea value was encountered in optimal conditions
in some clover/qrassland systems in New Zealancf,. Under our conditions; the quantity of
N,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 Nlfertilizer 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,algae
in the soik The amount of N-fixed by these organisms is much less than the amount fixed
symbiotically. 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, these
sources of Nl are not very sig,nificant.
Table 3-6,. Residual nitrogen provided by legumes.
legume
Time passed and
density of regume
Residual
nitrogen
(Ib/acre)
Alfalfa First year after alfalfa
50%-75% standi
25%-49% stand
0%-25% stand
Secondi year after alfalfa
50%-75%, sta'J11d
First' yearr afte'Fclover or.trefoil
25%-75-% standi
First yeas afte,/!'soybeans fOI grain
40
25
110
80
40
50
Red clover
and trefoil'
Soybeans
Source: PSU, 1990.
3.21