Pg. Hunt et Ta. Matheny, DRY-MATTER AND NITROGEN ACCUMULATIONS IN DETERMINATE SOYBEAN GROWN ONLOW-NITROGEN SOILS OF THE SOUTHEASTERN UNITED-STATES, Communications in soil science and plant analysis, 24(11-12), 1993, pp. 1271-1280
Reliable assessments of erosion potential, N fertilization need, and n
itrogen (N) non-point pollution potential for soybean [Glycine max (L.
) Merr.] cropping systems require accurate estimates of soybean dry ma
tter and N accumulations. The objective of this field study was to det
ermine dry matter and N accumulation in soybean during the growing sea
son and at harvest in samples large enough to reduce sample variation
and increase the confidence in measured values. A split-plot design wa
s used with cultivar (Braxton, Coker 338, and Davis) as the main plot
treatment and sampling date as the split-plot treatment. Each split-pl
ot contained eight rows 4.6 m in length on 0.75 m spacing. The seed we
re sown in a Norfolk loamy sand (fine-loamy, siliceous, thermic, Typic
Paleudult) on May 18 at the rate of 33 seeds/m. Water was applied by
use of an overhead irrigation gun. Plant samples were collected from 2
0 m2 of the six center rows on 89, 115, and 138 days after planting as
well as at seed harvest. Fallen plant material (crop litter) was coll
ected from each plot at each sampling date. Intact plant samples, crop
litter, and soil samples were analyzed for total Kjeldahl N. The mean
seed yield was 2.01 Mg/ha; the mean maximum dry matter accumulation f
or intact shoots plus crop litter was 10.2 Mg/ha, and the coefficients
of variation were <10%. The actual harvest index (seed yield/total dr
y matter accumulation) ranged from 0.19 to 0.28, and the mean maximum
N accumulation was 293 kg/ha. These accumulations are greater than tho
se reported for indeterminate soybean grown on high-N soils in the mid
western United States, and they clearly show that determinate soybean
grown in the southeastern United States accumulate substantial amounts
of dry matter and N.