Nitrogen Deficiency in Semi-Arid Kenya: Can Pigeonpea fix it?

ABSTRACT Few studies have evaluated improved pigeonpea varieties developed and released in Kenya for soil fertility improvement and contribution to the productivity of cereal-based cropping systems prevalent in marginal areas. A study comprising field and greenhouse experiments was conducted between 2009 and 2013, in order to evaluate improved pigeonpea varieties for nitrogen (N) uptake, biological nitrogen fixation (BNF), response to rhizobia inoculation and their effect on maize yields. Field experiments were conducted in Katumani Research Centre using a split-split plot design, with three pigeonpea varieties, two cropping systems and three crop residue regimes as the main plot, subplot, and sub-subplot, respectively. Greenhouse experiments were conducted at Muguga Research Centre where five pigeonpea varieties were screened for BNF and response to rhizobia inoculation in plastic pots filled with 10 kg of soil and replicated four times in a completely randomized design. Data collected on nitrogen uptake, BNF and maize and pigeonpea yields was subjected to analysis of variance using GENSTAT statistical software. Pigeonpea had significantly (p ≤ 0.05) higher nitrogen uptake compared with maize; Mbaazi II (84–114 kg N ha−1) absorbed more N, followed by Kat 60/8 (29–44 kg N ha−1) and Mbaazi I (20–37 kg N ha−1). All the three pigeonpea varieties fixed 60–70 kg N ha−1, meaning they were all good nitrogen fixers. Mbaazi II fixed significantly (p ≤ 0.05) higher N (70 kg N ha−1) compared with KAT 60/8 (66 kg N ha−1) and Mbaazi I (62 kg N ha−1) when intercropped with maize. Inoculation with rhizobia gave mixed results. Mbaazi II-maize intercrop gave the highest maize (1.9 t ha−1) and pigeonpea (1.4 t ha−1) grain yields and produced sufficient maize stover (2.1 t ha−1) and pigeonpea stalks (2.9 t ha−1).