Effect of Soil Types and Soil Moisture Stress on Growth and Yield of Upland Rice in Mwea, Kirinyaga County

Abstract

Drought is one of the most critical constraints to upland rice production in Kenya. To realize stable rain-fed upland rice production, it is important to introduce varieties that are minimally affected by water deficit. The soil water content relationship and soil penetration resistance are also important since this relationship varies with soil type and the root system development is suppressed when soil becomes harder with the progression of soil drying. In Kenya, soil type varies considerably, affecting areas in which rice is grown (or potentially grown). A study was conducted with the following specific objectives: (i.) to identify rice varieties that are tolerant to drought conditions under different soil moisture regimes; (ii) to assess the critical physiological traits associated with drought tolerance in rice; and (iii) to evaluate the best performing upland rice varieties in terms of growth and yield attributes. The study evaluated the performance of 20 rice varieties under different soil moisture regimes and soil types. The selected rice varieties had a maturity range of 90 to 120 days. The study was conducted at KALRO Mwea between December 2013 and July 2015. The experiment was set up in a randomized complete block design (RCBD) with a split-split plot arrangement, replicated three times. Soil moisture regimes (well-watered and water-deficit) were assigned to the main plot, soil types (black cotton, red clay, volcanic ash, and sandy clay) to sub-plots, and rice varieties to the sub-sub-plots. The experiment was conducted under controlled shelter to protect treatments from rain and other environmental factors. To assess the effects of water regime, soil type, rice variety, and their interactions on panicle weight and above-ground biomass, three-way analyses of variance (ANOVA) was conducted using Statistical Analysis System (version 9.0) (SAS Institute Inc., Cary, NC, USA). The study aimed to identify drought-resistant varieties suitable for different soil types in Kenya. The means of panicle weight and above-ground biomass in different water regimes and soil types were separated using the least significant difference (LSD) test at P<0.05 significance. Under water-deficit conditions, the reduction in soil water potential differed markedly according to soil type after terminating irrigation. The rice varieties tested were classified into four groups, broadly consistent with differences in rice variety ecotype. It was confirmed that lowland varieties such as Basmati 370 should not be considered a candidate for cultivation under rain-fed upland conditions in Kenya. Furthermore, the results revealed that even potentially high-yielding varieties might not attain their yield potential if the cultivation environment is unsuitable. Although five upland varieties (Dular, IRAT109, NERICA 1, NERICA 4, and Yumenohatamochi) presented relatively higher grain yield under water-deficit conditions in all soil types, individual variety's grain yield depended on the soil type. Their higher yield may have been attributed to certain root traits and their yield variations due to an interactive effect between root development and soil type. The results indicated that Dular, IRAT109, NERICA 1, NERICA 4, and Yumenohatamochi are suitable for cultivation under rain-fed upland conditions across the significant rice-growing areas in Kenya. Soil type should be considered when selecting varieties for a location's maximum productivity. Early-maturing varieties were identified as more suitable for drought-prone areas due to their shorter growing period.