Physiological and Developmental Response of Selected Rice Genotypes to Water and Nutrient Stress in Different Soils in Western Kenya

Abstract

Drought is a major challenge for all agricultural crops, but for rice, it is even more serious, becauseof its semi aquatic phylogenetic origins and the diversity of rice ecosystems and growing conditions. The most important source of climate-related risks for rice production in rainfed areasis drought. Crop physiology has made a significant contribution to understanding the mechanisms underlying crop growth and development, and bridging the "phenotype gap" generated by the recent progress in genomics. Some studies involving plant water status and photosynthesis in upland or lowland have been recorded , but a thorough analysis of below and aboveground plant biomass in relation to genetic (G) ,environment (E) and management (M) is stilllacking. Large genotypic variations have been found for roots in upland rice; however, quantitative comparisons between the deep root morphology of rice cultivars on upland fields and the effects of soil water conditions and nutrient load upon it are still limited. This study assumesthat the genotypic characteristics required for drought resistance would be determined as affected by site-specific, soil properties and fertilizer management, and that the assessment of G x E x M interaction is necessary requirement for enhancing and stabilizing the upland rice productivity under drought-prone environments. The study aimed to determine growth and physiologicalresponse of selected upland rice genotypes (IRAT 109, Lemont and NERICA 4) to waterdeficit, fertilizer application and in different soil types. This study was carried out in the University Botanic Garden, Maseno during September 2011 to January 2012. Plants were subjectedto water nutrient stress treatment in the field and in PVC tubes. Two experiments were conducted, field trial (Exp. 1) and PVC-tubes trial (Exp. 2). Experiment 1 had three fertilizer treatments, (N, P, and NP) and a control and only Nand NP for experiment 2. Experiment 1 and2 had, 2 and 3 genotypes respectively with 2-water managements, in a split-plot design. Exp. 2 had two-soils-type in Randomized Completely Blocked Design (RCBD). Water treatment startedat 42 das in Exp. 1 and 35 das in Exp. 2., fertilizer treatment, was applied at 60 Kgha-1N, and 60 Kgha·IN + 45 Kgha-1p, at 42 and 56 das; in Exp. 2, 80 Kgha-1N, 60 Kgha-\ P and 80 Kgha-1N+ 60 Kgha-1p, was applied in fertilized tubes, at 21 and 42 das. Shoots measurements at 21,42,63 and 84thdas, roots sampling at the same interval at depths of 0-10 em, 10-20 em, and 20-40Cm. the parameters measured included. soil moisture content, growth parameters, plant biomass, N content, stomatal conductance and yields. The parameters measured recorded a similartrend in the field and in the PVC tubes. The soil moisture content had significant effect and decreased with increasing water deficit. The growth parameters like plant height, plant biomass both shoot and root reduced with decreasing water content and nutrient load in the soil. The water stressed plant, Lemont, registered the lowest growth parameters. Lemont, being the most water stressed plant had the lower stomatal conductance and N content. The yield component declined in water stressed conditions, IRAT 109 had the highest yield while Lemont the least. Results indicates that under water-nutrient deficit, IRAT 109 has a superior physiological traits such as high stomatal conductance and high N foliar content hence can be recommended for growing under rainfed conditions in Kenya. This finding will ultimately help in poverty eradication through increased income and improved food security.