SOIL CHARACTERIZATION, EFFECTS OF NITROGEN SOURCES, TILLAGE METHODS AND CROPPING SYSTEMS ON SOIL PROPERTIES AND MAIZE (Zea mays L.) IN THE CENTRAL RIFT VALLY OF ETHIOPIA

Abstract

Declining soil fertility is one of the major challenges to crop production and productivity in Ethiopia. Thus, addressing this challenge through developing new techniques and application of integrated soil management practices tailored to a particular crop and location is vital to improve crop productivity and production. Given this, studies were conducted in two districts of the central rift valley of Ethiopia with objectives: (1) To characterize and identify the soils of the study areas (2) To evaluate the effects of compost, inorganic nitrogen fertilizer and their mixture on soil properties, growth, and nitrogen uptake of maize, and (3) To assess the combined effects of tillage methods, cropping system and nitrogen fertilization on selected soil chemical properties, maize performance; and organic carbon and total nitrogen stocks. Two pedons, one from each, site were excavated and characterized with respect to morphological, physical and chemical properties. Pot trials were executed using a factorial combinations of five compost rates (0, 5, 10, 15, and 20 t ha-1 ) and four inorganic nitrogen fertilizer rates (0, 46, 92, and 138 kg N ha-1 ), laid out as a completely randomized design with three replications. Field study was carried out using three-factors arranged as split-split plot arrangement in randomized complete block design with three replications. The tillage methods were used as the main plot, cropping system as a subplot, and four levels of nitrogen fertilization as the sub-sub plot. Maize variety BH 546 was used as a test crop. The results of soil characterization showed great differences in their morphological, physical, and chemical properties within and among the profiles. Accordingly, the soil of the Dore Bafeno site was classified as Cambisol (Loamic, Aric, Humic), whereas, the Bati Dubano site was classified as Someric Phaeozems (Pantoclayic, Aric). The analysis of variance showed that the combined application of compost and inorganic N fertilizer significantly improved soil chemical properties, plant growth, and nitrogen uptake, compared to the unfertilized or separate addition of compost and/or inorganic N fertilizer. Similarly, different soil management practices were significantly affecting grain yield, N-uptake xxviii and selected soil chemical properties. In both soils, the conventional tillage and haricot beanmaize rotation system increased the yield and yield components, and N-uptake in contrast to the minimum and maize monocropping, respectively. However, tillage methods differed in their effects on soil organic carbon and total nitrogen stocks, which were improved through MT compared to CT. Therefore, a CT plus haricot bean-maize rotation system with the addition of sole inorganic N at 92 kg ha-1 and integrated 46 kg N ha-1 + 10 t compost ha-1 should be recommended, to achieve better yield and yield components as well as N-use efficiency, for Cambisols in Hawassa Zuria and Phaeozems in Meskan study sites, respectively. Nevertheless, to ensure sustainable maize production in the studied soils, we recommended that the integrated application of 46 kg N ha-1 + 10 t ha-1 compost along with MT and legume-based crop rotation, which can enhance soil properties, and in the long run will improve yield, and N-uptake as well as utilization efficiency. This is because the field study was carried out only for two consecutive years and generated short-term results. Therefore, a longer-term study should be carried out at similar soils/sites to assess the long-term effects of tillage practices, cropping systems, and nitrogen fertilization on soil properties, and yield and yield components as well as nitrogen utilization efficiency