Sinclair, T.C.

English

Name not available

Photosynthate and nitrogen requirements for speed production by various crops

Wageningen Yield 

Reprinted from 
15 August 1975, Volume 189, pp. 565-567 
Photosynthate and Nitrogen Requirements for Seed Production 
by Various Crops 
T. R. Sinclair and C. T. deWit 
Copyright© 197.5 by the American Association for the Advancement of Science 
Photosynthate and Nitrogen Requirements for Seed Production 
by Various Crops 
Abstract. Seed biochemical composition was the basis for segregating 24 crops into 
four distinct groups. Nitrogen requirements of pulses and soybeans were so great that 
sustained seed growth demanded continued nitrogen translocation from vegetative tis-
sues. This translocation must eventually induce senescence in these tissues. restrict the 
duration of the seed-fill period. and limit seed yield. 
Seeds of crop species vary a great deal in 
their chemical composition and these dif-
ferences significantly influence their utility 
to man. The formulations of livestock feed 
or the diets of humans, for example, are 
based to a great extent on the relative pro-
portions of protein, carbohydrate, and lip-
id of the various available grains. Recently, 
attempts have been made through crop 
breeding to alter the chemical composition 
of seeds and thereby enhance their nutri-
tional and economic value. 
However, the impact of altering the 
chemical composition of seeds on the 
photosynthate and nitrogen relationships 
within the crop plant and, consequently, on 
crop productivity have rarely been consid-
ered. It has long been known that the ca-
loric values. of protein, carbohydrate, and 
0.4 0.5 0.6 0.7 0.8 
G. SEED/ G. PHOTOSYNTHATE 
Fig. l. Plot of milligrams of nitrogen required 
and grams of seed biomass yielded per gram of 
available photosynthate for the 24 crop species 
analyzed. The dashed lme represents the nitro-
gen requirement when the nitrogen supply rate 
is slg ha-l day-land the available photosynthate 
rate is 250 kg ha _, day-'. 
lipid are quite different. Assuming the 
leaves of a crop produce photosynthate at 
a fairly uniform rate and hence yield a con-
stant caloric output, it necessarily follows 
that changes only in the chemical constitu-
ents of seeds must alter biomass yield. An 
objective of this analysis was to compare 
the biomass yield per unit of photosynthate 
of seeds having different relative amounts 
of protein, carbohydrates, and lipid. In ad-
dition, altering the protein content of seeds 
also changes the amount of nitrogen re-
quired in the production of seed biomass. 
Since nitrogen fertilization is recognized as 
a critical factor in crop production, 
changes in nitrogen demand resulting from 
alterations of seed composition may re-
quire a reevaluation of management tech-
niques for crop nitrogen supplies. There-
fore, a second objective of this analysis was 
to examine the nitrogen requirements of 
seeds with varying protein contents. 
The relative amounts of protein, car-
bohydrates, lipid, and ash (on the basis of 
fresh weight) of 24 crop seeds were used in 
this analysis (1). All data were first con-
verted to dry weight and a wide range in 
the relative composition of seeds was ob-
tained (see Table 1 ). The ranges for the rel-
ative amount of protein, carbohydrate, and 
lipid were 8 to 38 percent, 19 to 88 percent, 
and 1 to 54 percent, respectively. While the 
data for a given species may. be unrepre-
sentative of some genotypes within the spe-
ci.es, the range in these data allows eval-
uation of the seed biomass production and 
nitrogen requirements of cultivars with dif-
fering chemical compositions. 
The relative seed compositions were first 
used to calculate the photosynthate re-
quirements for biomass production. The 
results of an exhaustive examination of the 
biochemical pathways for the production 
of proteins, carbohydrates, and lipids from 
l 
\ 
glucose by Penning de Vries (2) were used. lations are required to account for nitrogen even when the photosynthetic productivi-
His analysis showed that the biomass con- supplied to the seeds by redistribution ties of the crops are equal. Similarly, a 
versions were, in fact, fairly insensitive to from the vegetative tissues, which is not ni- wide range of nitrogen requirements were 
the synthesis pathway and the sub- trate. calculated among the crops~ Rice had- the 
~ffl13eite~HHH5fH:i--pFGGuGts~~e~f~ow,UrJ.wd~-:-T.Lllh~e~nLlJi":'-t rw.oli:g~e~n __ ure~qp..tui ure;<~.dLYb~y-'t~hts;e'-.Js~e~e:,ydL;_ ·.nW:.!:!aAs_1~9~W~e~s~t~d~e~m~_~a:!:nd~,l--..!.re~g~u~i~ri~n!J;;gL_ ~o~n!,;ly~_ ~1~0~--~m~g~ _ _;o;!_f_. --~-J 
that from 1 unit of glucose· about 0.83 unit also tabulated by first calculating the mass nitrogen per gram of photosynthate, while 
of carbohydrates, 0.40 unit of protein (as- of protein produced per unit mass of avail- soybean was the highest with a require-
suming nitrate to be the nitrogen source), able photosynthate. 'y'/e assumed protein ment of 29 mg of nitrogen per gram of 
or 0.33 unit of lipid could be produced. was 15 percent nitrogen by weight in order photosynthate. This threefold difference is 
Knowing the relative composition of the to estimate the milligrams of nitrogen re- not as large as the difference in protein 
seeds and these constituent conversions, we qui red per gram of photosynthate for each content among the crops, but significant 
tabulated a conversion coefficient for the species (see Table 1).·· variability among species in their nitrogen 
production of whole seed from glucose for These calculations resulted in yield esti- requirements is suggested. 
each species. These data, expressed as mates of seed biomass from 1 g of photo- To visualize more easily the differences 
grams of seed biomass produced per gram synthate ranging from 0.42 g for sesame to among the crops, the nitrogen require-
of photosynthate (that is, glucose), are 0.75 g for barley and rice, which suggests ments per gram of photosynthate were 
presented in Table 1. More detailed calcu- an almost twofold difference in seed yield plotted in Fig. 1 against biomass produc-
Table l. Chemical composition, biomass productivity (grams of seed per gram of photosynthate), 
and nitrogen requirement (milligrams of nitrogen per gram of photosynthate) of seeds of 24 crop 
species. 
Species 
Barley (Hordeum 
vulgare) 
Bean, lima (Phaseolus 
vulgaris mac.) 
· Bean, mung (Phaseolus 
aureus) 
Chick pea (Cicer 
arietinum) 
Corn (Zea mays) 
Cotton ( Gossypium 
hirsutum) 
Cowpea (Vigna 
sinensis) 
Flax (Linum 
usilatissium) 
Hemp (Cannabis 
sativa) 
Lentil (Lens 
culinaris) 
Oat (Avena 
sativa) 
Pea (Pisum 
sativum) 
Peanut (A rachis 
hypogaea) 
Pigeon pea (Cajanus 
cajan) 
Popcorn (Zea 
mays praecox) 
Rape (Brassica 
nap us) 
Rice (Oryza 
sativa) 
Rye (Seca/e 
cereal e) 
Safflower (Carthamus 
tinctorius) 
Sesame (Sesamum 
indicum) 
Sorghum (Sorghum 
vulgare) 
Soybean (Glycine 
max) 
Sunflower (Heliantus 
ann us) 
Wheat (Triticum 
escu/entwn) 
Composition (percentage of dry weight) 
Carbo-
hydrate 
80 
70 
69 
68 
84 
47 
69 
32 
27 
67 
77 
68 
25 
69 
80 
25 
88 
82 
50 
19 
82 
38 
48 
82 
Pro-
tein 
9 
24 
26 
23 
10 
25 
26 
26 
29 
28 
13 
27 
27 
25 
13 
23 
8 
14 
14 
20 
12 
38 
20 
14 
Lipid 
2 
5 
5 
25 
2 
38 
41 
5 
2 
45 
2 
5 
48 
2 
2 
33 
54 
4 
20 
29 
2 
Ash 
4 
4 
4 
4 
I 
3 
3 
4 
3 
4 
5 
3 
3 
4 
2 
4 
2 
2 
3 
7 
2 
4 
3 
2 
Biomass 
produc-
tivity 
(g/g) 
0.75 
0.67 
0.66 
0.64 
0.71 
0.52 
0.66 
0.46 
0.44 
0.65 
0.70 
0.65 
0.43 
0.66 
0.69 
0.43 
0.75 
0.72 
0.52 
0.42 
0.70 
0.50 
0.51 
0.71 
Nitrogen 
require-
ment 
(mgjg) 
ll 
25 
26 
23 
11 
20 
26 
18 
20 
28 
14 
27 
18 
26 
14 
15 
10 
15 
11 
13 
13 
29 
15 
16 
tion per gram of photosynthate. The crops 
segregated into four distinct groups. In the 
lower right-hand quadrant of Fig. 1 are the 
grain-cereal' crops that have been tradi-
tionally the world's staple crops. These 
seeds are characterized by low protein and 
lipid contents. In the lower left-hand quad-
rant is a slightly more scattered group of 
crops containing most of the world's oil 
crops, which have the common character-
istic of high lipid contents. Their yields are 
only about 60 percent of the grain yields, 
which is in good agreement with the yield 
ratio of rape seed and wheat in the Nether-
lands. The upper right-hand quadrant con-
tains crops that are low in lipid content but 
have fairly high protein contents. This 
group contains many of the pulse crops 
grown for human consumption. Soybeans 
are the sole crop in the remaining quad-
rant, which demonstrates its uniqueness 
among the world's crops in bo.th the com-
position of its seed and potential limita-
tions to its productivity. Soybeans not only 
require the greatest amount of nitrogen in 
seed production but. are also one of the 
lowest producers of seed biomass per unit 
of photosynthate. 
By assuming rates of crop photosyn-
thate production and nitrogen uptake from 
the soil, further distinctions among the 
crop species can be made based on the ni-
trogen balance. We estimate that healthy, 
adequately fertilized crops will produ~e 
photosynthate for seed production at a rate 
of about 250 kg ha-1 day-'. A nitrogen up-
take rate of 5 kg ha-1 day-' is in the range 
of maximal uptake rates for many crops. 
Division of the estimated nitrogen uptake 
rate by the photosy.nthate production rate 
yields an estimate of the nitrogen supply to 
the seed from the soil of 20 mg of nitrogen 
per gram of photosynthate. This nitrogen 
supply, shown as the horizontal dashed line 
in Fig. 1, is sufficient only to satisfy the ni-
trogen demands of 1he crops in the two 
lower quadrants. The species in the top 
part of Fig. 1 are not able to meet the total 
nitrogen demand generated by the seed tensive nitrogen translocation to the seeds portance of nitrogen availability and sup· 
from the nitrogen supplies available from from vegetative tissue, a shorter period of ply on crop yields. The seed yields of crop 
the soil. Increasing the nitrogen uptake seed development, and lower total yield species identified as self-destructive may be 
rate to 6 kg ha- 1 day-' increases the supply (4);. significantly inhibited by insufficient rates 
to 24 mg ()f mfr()gen ·pet gramn oTplT~Hftfr~~e~~0-e --uOtL-unuit+JfOIJ.lg~e;.IJn~-;ss..~.1 LJ.IPlfPU.:IY'f.. _Twhwe;:..bo.t4l. g~bwr:aaJJte~swowfwnruillt r::co~;-___ -J 
gen uptake demanded by the seeds of these cies would be unresponsive to nitrogen fer-
tilization unless it increased directly the 
rate of nitrogen uptake by the plant during 
seed-fill. The inability of the self-destruc-
tive crops to respond to nitrogen fertilizer 
is aggravated beca~se many of these spe-
cies support symbiotic nitrogen fixation, 
which tends to decrease in proportion to 
nitrogen fertilization. In soybeans the 
yields of a nodulating genotype were essen-
tially unchanged by nitrogen fertilization, 
while the yields of a nonnodulating isoline 
increased with fertilization, reaching those 
of the nodulating genotype (5). 
thate and leaves the division between the 
crop groups nearly unaffected, with only 
chick pea moving below the line. 
For the crop species in the top part of 
Fig. l to sustain the calculated rates of 
seed biomass production, wr;; hypothesize 
that the remaining nitrogen demand must 
be obtained from· the vegetative plant 
parts. Experimental observations of nitro-
gen mobilization and translocation from 
leaves to seeds during seed development 
support this hypothesis (3). Since the pool 
of nitrogen and protein in vegetative tis-
sues will be continually depleted, the vege-
tative tissues must eventually lose physi-
ological activity as the nitrogen levels de-
crease and ·the plant becomes .. self-de-
structive." Many of these self-destructive 
species in the top part of Fig. 1 exhibit leaf 
senescence and abscission during seed de-
velopment. Final seed yield of these species 
may also be closely tied to the self-destruc-
tive characteristic. Since the duration of 
the seed development period is obligatorily 
linked to productive vegetative tissues, if 
seed development eventually impairs the 
physiological activity of vegetative tissues, 
seed production in the self-destructive spe-
cies is inherently limited to a finite length 
of time for seed-fill. Therefore, the dura-
tion of the seed development period is in-
timately tied to the rate of nitrogen uptake 
by the self-destructive crop during seed-
fill. A low rate of uptake results in a 
large nitrogen demand and leads to ex-
For the species in the lower portion of 
Fig. 1 seed growth may be sustained by a 
relatively small rate of uptake of nitrogen 
during the seed-filling period without the 
necessity of nitrogen redistribution within 
the plant. However, these species may also 
translocate nitrogen during seed devel-
opment and the total amount of nitrogen 
available from the soil is often finite, so 
that self-destruction may also develop in 
the species in the lower portion of Fig. l. 
Nitrogen fertilization may at least partial-
ly alleviate the limitation of nitrogen avail-
ability in the soil and minimize the effects 
of the self-destructive process in these spe-
cies. This agrees with the w.ell-established 
phenomenon that nitrogen fertilization of 
small grains increases yield by postponing 
senescence. 
Our analysis of the chemical composi-
tion of crop seeds shows the potential im-
species may cause the rapid translocation 
of nitrogen from the vegetative plant parts. 
The destruction of. proteins in vegetative 
plant parts leads to a loss in physiological 
activity and senescence of the plant, and a 
shortened period for seed development. 
The remaining species are not generally 
limited by the potential rate of nitrogen 
supply from the soil but rather the total 
amount of available nitrogen. 
T. R. SINCLAIR* 
c. T. DE WIT 
Department ofTheoretical Production 
Ecology, Agricultural University, 
Wageningen, Netherlands 
References and Notes 
l. W. S. Spector, Ed., Handbook of Biological Data 
(Saunders, Philadelphia, 1956), p. 87. 
2. F. W. T. Penning de Vries, in Photosynthesis and 
Productivity in Different Environments, J. P. 
~ooper, Ed. (Cambridge Univ. Press, Cambridge, 
tn press). 
3. J. J. Hanway and C. R. Weber, Agron. J. 63,227 
(1971); ibid., p. 406; H. S. McKee, Nitrogen Me-
tabolism in Plants (Clarendon Oxford 1962) p 728. ' • ' . 
4. T. R. Sinclair and C. T. de Wit, in preparation. 
5. C. R. Weber, Agron. J. 58,43 (1966). 
6. Suppor.ted in part by the Agricultural University, 
Wagenmgen, Netherlands, and in part by the 
Eastern Deciduous Forest Biome U.S. lnter-
n.ational ~iological Progr.am, fund~d by the Na-
tional Sctence FoundatiOn under interagency 
agreement AG 199,40-193-69 with the Energy Re-
se:'\rch an~ Development Administration, Oak 
Rtdge NatiOnal Laboratory. Contribution No. 224 
from the Eastern Deciduous Forest 2iome. 
• Pre~ent address: U.S. Department of Agriculture; 
Agncultural Research Service, Corne11 University,· 
Ithaca, New York 14853. 
5 May 1975 


Photosynthate and nitrogen requirements for speed production by various crops

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