Phosphorus requirement and sources of nitrogen in three soybean (Glycine max) genotypes, Bragg, nts 382 and Chippewa

Abstract

The effect of different levels of soil phosphorus on nodulation, N z fixation and growth of supernodulating soybean mutant, nts 382, its parent, Bragg, and soybean cultivar, Chippewa, were compared in a greenhouse study. The P rates were, 0, 30, 60 and 90 mg kg -1 soil (P0, PI, P2 and P3, respectively).The reduced shoot growth of nts 382 (25% at P0 and 17% at P3) could not be attributed to P deficiency, as nts 382 achieved near maximum yield at a lower P rate (P1) than Bragg (Pz). The P response of Chippewa that produced the lowest shoot yield, was similar to that of Bragg. Root growth of nts 382 was more retarded than shoot growth (on average 50% that of Bragg), and yet absorbed a similar amount of total P as Bragg. Also, Chippewa that had the lowest root dry matter accumulated the highest P in the shoots. The data indicate that plant growth was influenced by differences in P use efficiency rather than differences in total P.In contrast to plant growth, nts 382 accumulated 26% more N than Bragg, and Chippewa accumulated a similar amount of N as Bragg. Thus again, Bragg used N most efficiently for growth. Soil N uptake was not governed by root biomass, and Chippewa absorbed more N from soil than both Bragg and nts 382 which absorbed similar amounts of soil N. Nodulation in nts 382 was significantly enhanced, being 528 and 892% greater than Bragg at P0 and P3, respectively, and nts 382 was the only cultivar whose nodulation was consistently enhanced by P addition. The percentage of N derived from fixation (% Ndfa) was not affected by supernodulation, but because of a greater accumulation of total N in nts 382, amount of N fixed (Ndfa) was on average 30% higher in nts 382 than Bragg. Also, while % Ndfa in either nts 382 or Bragg was not influenced by P addition, total N and consequently, Ndfa increased. However, for Chippewa which fixed the lowest N, both % Ndfa and Ndfa were increased by P addition. We conclude that although supernodulation had an adverse effect on shoot and root growth, these reductions could not be attributed to a reduced uptake of the two major plant nutrients, N and P, neither was there evidence that the mutation had caused a greater demand for these nutrients, other than for the greater requirement of P for nodulation.

Relative Values of Physiological Parameters of P Response of Different Genotypes can be Measured in Experiments with Only Two P Treatments

“…Although the required SE's are generally not given in the literature it is nevertheless possible to make semi-quantitative estimates of Km. We found near proportional relationships between W1 and W2 for genotypes of Zea mays L. (Fageria and Baligar, 1997), of Phaseolus vulgaris L. (Aggarwal et al, 1997), of Glycine max (Gunawardena et al, 1993), and of various leguminous cover crops (Tian et al, 1998) all of which support the view that for these species inter-genotypic variation in Km is small. Highly significant linear relationships between grain yields of crops grown with deficient P and those grown with adequate P have been reported for 364 landraces, cultivars and wild genotypes of common bean (Beebe et al, 1997).…”

“…Greenwood et al, 1980). Thus, it should be possible, by cropping with cultivars that grow well on low P soil to increase phosphate use efficiency (PUE) defined as yield per unit loss of plant available P. Intra-species variation in the ability of crop plants to grow well on low P soils has often been reported (Fageria and Baligar, 1997;Gunawardena et al, 1993;Sanginga et al, 2000) but the reasons for these differences have not been fully elucidated. It is an objective of crop physiologists and breeders to identify genes responsible for intra-species differences in P-response by QTL analysis (Kearsey and Farquhar, 1998) and then to use this information as a basis for developing cultivars that utilise P more effectively.…”

Grain Legumes

“…Differences in N 2 fixation related to the efficiency of utilization of P were also found among soya bean genotype (Guanawardena et al 1993) andA. mangium populations (Vadez et al 1995).…”

Genotypic variability in phosphorus use efficiency for symbiotic N2 fixation in common bean (Phaseolus vulgaris)

“…[16] and Acacia mangium [27,31], showing that P requirements are generally higher for N 2 fixation than for shoot growth and mineral N assimilation, since nodules are an additional strong sink for P. Furthermore P requirements for N 2 fixation varies between genotypes in pigeon pea (Cajanus cajan) [1] and mungbean (Vigna radiata) [11], or Casuarina-Frankia symbioses [29]. Differences in N 2 fixation related to the efficiency in utilization of P were found among soybean genotypes [11], and Acacia mangium populations [32]. According to Cassman [4], efficient P utilization in N 2 -fixing symbioses may be closely related to an adequate P partitioning between shoot and nodulated root, and between root and nodules.…”