Paper Reviewed
Lenka, N.K., Lenka, S., Singh, K.K., Kumar, A., Aher, S.B., Yashona, D.S., Dey, P., Agrawal, P.K., Biswas, A.K. and Patra, A.K. 2019. Effect of elevated carbon dioxide on growth, nutrient partitioning, and uptake of major nutrients by soybean under varied nitrogen application levels. Journal of Plant Nutrition and Soil Science 182: 509-514.

Field studies on the interactive effects of elevated CO2 and nitrogen (N) supply on plant metabolism and nutrient assimilation remain scarce for soybean. To help remedy such lack of data, Lenka et al. (2019) recently investigated the effects of elevated CO2 and various levels of N supply on the biomass, grain yield, nutrient concentration and uptake of soybean.

The work was conducted in open-top chambers at a research farm of the Indian Institute of Soil Science, Bhopal, Pune, India in 2016. The two CO2 concentrations investigated were ambient (395 ppm) and elevated (535 ppm, applied during daylight hours only) and the four N-supply levels included 0, 50, 100 and 150% of the normal recommended dose. Two other nutrients, phosphorus (P) and potassium (K), were supplied in each treatment at their normal recommended dose. The soybean cultivar utilized in the experiment was JS-20-29.

In discussing their findings, the ten Indian researchers report that both elevated CO2 and N-supply positively impacted soybean growth and yield. Aboveground biomass of soybean at harvest, for example, increased by 40, 38, 65 and 30% in the 0, 50, 100 and 150% N supply treatments, respectively. Similarly, soybean seed yield increased by 39, 59, 51 and 26% in the 0, 50, 100 and 150% N supply treatments, also respectively (see Figure 1). Furthermore, under elevated CO2, the highest aboveground biomass and seed yield values occurred in the normal N supply treatment (i.e., 100% of N supply recommendation), whereas under ambient CO2 they occurred in the 150% of normal N treatment.

Lenka et al. also found that soybean seed N and K concentrations were unaffected by either CO2 or N application. Seed P concentration, on the other hand, was reduced in all N applications under elevated CO2 with the exception of the highest N supply treatment. More specifically, seed P decreased by 7, 9 and 3% in the 0, 50% and 100% N-supply treatments, whereas it increased by 7.5% at the highest N-supply level (150% of normal). Nevertheless, despite the relative decline in seed P concentration at elevated CO2, the total plant P uptake significantly increased by 23-62% depending on N-supply level. Elevated CO2 also stimulated plant N and K uptake by 18-61% and 22-62% at the various N treatments.

In summarizing the above findings, both elevated CO2 and N-supply improve soybean seed yield, with the greatest yield value observed under elevated CO2 and 100% of the recommended supply of N. And these yield gains come with no effect on seed N or K concentration and only minimal decline of P concentration, which decline would most likely be overcome with the application of a little more P-supply as a soil management technique. Thus, the future looks very bright for the production of soybean.

Figure 1. Soybean seed yield under ambient (395 ppm) or elevated (535 ppm) CO2 and 0% (N0PK), 50% (N50PK), 100% (N100PK) or 150% (N150PK) of recommended soil nitrogen levels. The red text indicate the percent increase in seed yield due to elevated CO2 for a given N-supply treatment. Source: Adapted from Lenka et al. (2019).