Pigeonpea Response to Silicon, Phosphorus, and Rhizobium Inoculation in an Acid Coastal Plain Soil

ABSTRACT

Pigeonpea [Cajanus cajan (L.) Millsp.] is a legume with potential as an alternative summer crop in the U.S. Southern Coastal Plain. It has low fertilizer and pesticide requirements, and is used for both animal feed and human food. Southern coastal plain soils are acidic and phosphorus (P) deficient before liming and fertilization. Under those conditions, pigeonpea is limited in its ability to symbiotically fix atmospheric nitrogen (N₂). Calcium silicate application can reduce the adverse effects of soil acidity and also enhance the availability of P in such soils. The effects of calcium silicate on P availability and the effects of Rhizobium inoculation on the growth of pigeonpea on a Greenville soil from the coastal plain of Georgia were investigated in laboratory and greenhouse experiments. Both silicon (Si) and P applications significantly increased the growth of pigeonpea. Optimum fresh and dry shoot weights, plant-available water, shoot height, nitrogen (N) and P contents, and P:manganese (Mn) ratios were found when 1.96 g Si/pot (4.48 t Si/ha) was applied as calcium silicate. High levels of plant Mn concentrations were reduced by such application. Application of 0.1 g P/pot (39 kg P/ha) produced the optimum fresh and dry shoot weights, plant water content, and shoot height. Inoculation had no effect on plant growth. There were no interactions for growth among Si, P, and inoculation. Increased growth due to Si application was adduced to increased available N and P and reduced levels of Mn. Applied Si also increased plant-available water, which enhanced leaf erectness—an important factor in light interception and therefore in growth. Low soil-available P was increased by fertilizer P, resulting in increased growth. Although Si is not an essential element, calcium silicate improved the growth of pigeonpea grown on this low pH soil.

ACKNOWLEDGMENTS

The authors acknowledge support from the Center for International Exchange of Scholars (CIES); the U.S. Department of State for funding C. Gerroh under the Fulbright Senior Scholars Award; and the College of Agricultural and Environmental Sciences, University of Georgia. The technical assistance provided by B. H. Baldree and Cindy Roesel is also appreciated.

Notes

* Mehlich-1 extractable phosphorus.

** Determined according to Korndorfer et al. (2001).

*** Regression significant at p = 0.05 and 0.01, respectively, by analysis of variance.

†Q = Quadratic, L = linear.

* Regression significant at p = 0.05 by analysis of variance.

^ns Regression not significant by analysis of variance.

†Q = Quadratic, L = linear.