Integrated eects of mineral nutrition on legume performance
P.M. Chalk*
Soil and Water Management & Crop Nutrition Section, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, International Atomic Energy Agency, P.O. Box 100, A-1400 Vienna, Austria
Received 15 June 1999; received in revised form 8 September 1999; accepted 30 September 1999
In their review of the role of phosphorus in nitrogen ®xation in upland crops, McLaughlin et al. (1990) drew attention to the diculty of isolating the eect of P supply on host plant growth from the eect of P on N2 ®xation per se, particularly in ®eld experiments.
These authors outlined three traditional approaches, which have attempted to separate the two eects, but none are considered to be satisfactory.
. Interaction with inorganic N. If the interaction
between added N and added P on legume growth is negative, then a speci®c eect of added P on N2
®x-ation may be inferred. However, positive rather than negative interactions have often been observed (McLaughlin et al., 1990).
. N concentration in the plant. If P application
enhances both legume biomass and N concentration, then a speci®c eect of P on N2®xation may be
pro-posed. However, improved N nutrition can derive from improved exploitation of soil N by more vigor-ous root growth due to amelioration of P-de®ciency.
. Number or mass of nodules or acetylene reduction
ac-tivity. It has been shown that nodulation parameters are often poorly correlated with estimates of N2
®x-ation (e.g. Kucey et al., 1988b), while assay pro-cedures provide a point-in-time rather than an integrated estimate of the rate of biological N2
®x-ation.
McLaughlin et al. (1990) mentioned another approach (15N balance) but they did not elaborate. The purpose of this short communication is to demon-strate how the 15N isotope dilution technique
(McAu-lie et al., 1958) can provide an unequivocal resolution of the two eects. The advantage of the isotopic method is that it provides both a yield-independent and time-integrated estimate of the proportional dependence of the legume on symbiotic N2 ®xation
(Patm). These characteristics enable the eect of any
treatment on N2 ®xation per se to be separated from
an eect on legume growth during the period between sowing and harvest (Chalk and Ladha, 1999).
The application of this technique to investigate nutritional constraints to legume performance is illus-trated by examples of data published in the literature. The data of Cadisch et al. (1993) show that addition of K to a K-de®cient soil increased dry matter yield of
Centrosema, whereas the rhizobium symbiont func-tioned very eciently in the presence of K-de®ciency
Patm0:93 and did not respond to K addition
(Table 1). The soil was also de®cient in P, but in this case both Patm and dry matter yield responded
posi-tively to P addition (Table 1). Ssali and Keya (1986) obtained a similar result for common bean (Phaseolus vulgaris) in a P-de®cient soil (Table 1).
The data of Shock et al. (1984) also show a dra-matic eect of S-de®ciency on both Patm and the dry
matter yield of subclover (Table 1). When the soil S-de®ciency was corrected yield increased 3-fold and the proportional dependence on N2 ®xation almost 4-fold,
with the result that the amount of ®xed N increased more than 12-fold. These data (Table 1) clearly show that dry matter and symbiotic dependence can both be adversely aected by severe nutrient de®ciencies. De-®ciency of Mo would similarly be expected to have a severe detrimental eect on both biomass production and Patm, although the author is unaware of any
pub-lished 15N dilution data which illustrate the integrated eects of Mo on legume performance.
Soil Biology & Biochemistry 32 (2000) 577±579
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In situations where nutritional stresses are less severe, there may be a penalty on dry matter yield without a signi®cant eect on Patm. For example, dry
matter yields of four legumes (Medicago sativa, Trifo-lium pratense, Vicia faba, Pisum sativum) were reduced by S-de®ciency but Patm was not aected (Scherer and
Lange, 1996). Similarly, addition of P fertilizer increased grain yield in soybean (Rennie et al., 1988) and lentil (Bremer et al., 1989) and the biomass of
Leucaena (Sanginga et al., 1991) without signi®cantly aecting Patm.
In addition to nutritional constraints, there are sev-eral examples of the application of the 15N dilution technique to gather information on other impediments to legume performance. For example, Smith et al. (1993) showed that white clover responded negatively to induced soil salinity (saline irrigation water) through reduced dry matter yields but not through reduced symbiotic dependence, which remained very high. On the other hand, Smith (1999) found that both dry mat-ter yield and Patmof faba bean responded positively to
the amelioration of soil sodicity through application of gypsum. Water stress is another factor which can adversely eect both dry matter and Patm, with the
symbiotic dependence of soybean being relatively more aected than biomass production (Kucey et al., 1988a; Kirda et al., 1989).
The examples provided above illustrate that the 15N dilution technique can provide unique information on the relative sensitivity of the rhizobium symbiosis and the legume itself to edaphic and environmental stres-ses. Such information cannot be obtained by nonisoto-pic methodologies. The lack of a response to legume inoculation may be due to the existence of an ecient resident rhizobial population in the soil, or to some other factor limiting legume growth. The isotope
meth-odology can provide insight on constraints to legume or inoculant performance, which is crucial in the for-mulation of management strategies to maximise the bene®ts of legumes in cropping systems.
References
Bremer, E., van Kessel, C., Karamanos, R., 1989. Inoculant, phos-phorus and nitrogen responses of lentil. Canadian Journal of Plant Science 69, 691±701.
Cadisch, G., Sylvester-Bradley, R., Boller, B.C., NoÈsberger, J., 1993. Eects of phosphorus and potassium on N2 ®xation (15 N-di-lution) of ®eld-grown Centrosema acutifolium and C. macrocar-pum. Field Crops Research 31, 329±340.
Chalk, P.M., Ladha, J.K., 1999. Estimation of legume symbiotic dependence: an evaluation of techniques based on 15N dilution. Soil Biology & Biochemistry 31, 1901±1917.
Kirda, C., Danso, S.K.A., Zapata, F., 1989. Temporal water stress eects on nodulation, nitrogen accumulation and growth of soy-bean. Plant and Soil 120, 49±55.
Kucey, R.M.N., Chaiwanakupt, P., Arayangkool, T., Snitwongse, P., Siripaibool, C., Wadisirisuk, P., Boonkerd, N., 1988a. Nitrogen ®xation (15N dilution) with soybeans under Thai ®eld conditions. II. Eect of herbicides and water application schedule. Plant and Soil 108, 87±92.
Kucey, R.M.N., Snitwongse, P., Chaiwanakupt, P., Wadisirisuk, P., Siripaibool, C., Arayangkool, T., Boonkerd, N., Rennie, R.J., 1988b. Nitrogen ®xation (15N dilution) with soybeans under Thai ®eld conditions. I. Developing protocols for screening
Bradyrhizobium japonicumstrains. Plant and Soil 108, 33±41. McAulie, C., Chamblee, D.S., Uribe-Arango, H., Woodhouse Jr,
W.W., 1958. In¯uence of inorganic nitrogen on nitrogen ®xation by legumes as revealed by15N. Agronomy Journal 50, 334±337. McLaughlin, M.J., Malik, K.A., Memon, K.S., Idris, M., 1990. The
role of phosphorus in nitrogen ®xation in upland crops. In: Phosphorus Requirements for Sustainable Agriculture in Asia and Oceania. International Rice Research Institute, Los BanÄos, Philippines, pp. 295±305.
Rennie, R.J., Rennie, D.A., Siripaibool, C., Chaiwanakupt, P., Boonkerd, N., Snitwongse, P., 1988. N2 ®xation in Thai soy-beans: eect of tillage and inoculation on15N-determined N2 ®x-Table 1
Response of dry matter yield and symbiotic dependence of grain and forage legumes to the amelioration of nutrient de®ciencies
Reference Legume Nutrient Yield (g mÿ2)a
Form Rate (g mÿ2) Dry matter Fixed Nb
Cadisch et al. (1993) Centrosema macrocarpum K, P 0, 7.5 81 2.08 (0.93)
3, 7.5 137 3.26 (0.93)
6, 7.5 158 4.02 (0.94)
6, 0.5 50 0.97 (0.79)
6, 4.0 102 2.38 (0.92)
LSD0.05 25 0.68 (0.03)
Ssali and Keya (1986) Phaseolus vulgaris P 0 454 1.8 (0.16)
15 681 5.7 (0.32)
Shock et al. (1984) Trifolium subterraneum S 0 621 2.9 (0.20)
1 1373 16.7 (0.61)
8 1960 36.4 (0.75)
a
Data forCentrosemaare for shoots harvested 14 weeks after sowing; data forPhaseolusare for shoots harvested 74 days after sowing. b
Data in parentheses are Patmdetermined by15N dilution using as the non®xing reference plants,Melinis minuti¯oraforCentrosema,Hordeum vulgarefor common bean andBromus mollisandErodium botrysfor subclover.
P.M. Chalk / Soil Biology & Biochemistry 32 (2000) 577±579
ation in recommended cultivars and advanced breeding lines. Plant and Soil 112, 183±193.
Sanginga, N., Bowen, G.D., Danso, S.K.A., 1991. Intraspeci®c vari-ation in growth and P accumulvari-ation of Leucaena leucocephala
andGliricidia sepiumas in¯uenced by soil phosphate status. Plant and Soil 133, 201±208.
Scherer, H.W., Lange, A., 1996. N2®xation and growth of legumes as aected by sulphur fertilization. Biology and Fertility of Soils 23, 449±453.
Shock, C.C., Williams, W.A., Jones, M.B., Center, D.M., Phillips,
D.A., 1984. Nitrogen ®xation by subclover associations fertilized with sulfur. Plant and Soil 81, 323±332.
Smith, A. P., 1999. Nutrient cycling and grain legume nitrogen ®x-ation in ameliorated sodic soils. M. Agr. Sc. thesis, University of Melbourne.
Smith, C.J., Chalk, P.M., Noble, C.L., Prendergast, J.B., Robertson, F., 1993. Nitrogen ®xation in a white clover-grass pasture irri-gated with saline groundwater. Irrigation Science 13, 189±194. Ssali, H., Keya, S.O., 1986. The eects of phosphorus and nitrogen
fertilizer level on nodulation, growth and dinitrogen ®xation of three bean cultivars. Tropical Agriculture (Trinidad) 63, 105±109.
