Sustainable Management and Improvement of Soil Physical Properties and Rice Grain Yield in Degraded Inland Valleys of Southeastern Nigeria

Nigeria is relatively blessed with rain and high potential of inland valleys. The major constraints in the utilization of these inland valleys for sustainable rice based cropping include, poor soil properties maintenance, inadequate weed and water control. In an attempt to replicate the successful Japanese Satoyama watershed management model in the African agro-ecosystems, sawah rice cultivation technology has been introduced to West Africa in the last two decades. This study was conducted in an inland valley at Akaeze, Ivo Local Government Area of Ebonyi State, Southeastern Nigeria, in 2010, 2011 and 2012 cropping seasons, to evaluate the effects of four different tillage specifications and different amendments under sawah water management system on soil properties and rice grain yield. Sawah has been described as an Indo-Malaysian word for padi (Malayan word for paddy) or lowland rice management system comprising bunding, puddling, levelling and good water management through irrigation and drainage. A split- plot in a randomized complete block design was used to evaluate these two factors. The four tillage specifications for rice growing are; complete sawah tillage- bunded, puddled and leveled rice field (CST); farmers tillage environment- no bunding and leveling rice field (FTE); incomplete sawah tillage- bundding with minimum leveling and puddling rice field (ICST) and partial sawah tillage- after bunding, no puddling and leveling rice field (PST). The five levels of manure application including the control, which were replicated three times included; rice husk at 10 ton/ha; rice husk ash at 10 ton/ha; poultry droppings at 10 ton/ha; N. P. K. 20: 10: 10 at 400kg/ha and the control (Zero application). The study was undertaken in 3 cropping seasons (2010, 2011 and 2012) using the same watershed and treatments. The effects of additive residual effects of the amendments were not studied in the course of this research. A bulk soil sample at 0-20 cm depth and core samples were collected in the location before tillage and amendments for initial soil characteristics. At the end of each harvest of the three cropping seasons, another soil sampling was carried out on the different treated plots to ascertain the changes that occurred in the soil due to the treatments application. Selected physical analyses were carried on those soils collected, while the soil amendments were analyzed for N, P, K, Ca, Mg, Na, and organic carbon. The soil physical properties analyzed for included; soil BD, total porosity, mean weight diameter, water retention and saturated hydraulic conductivity. The soil bulk density (BD) was significantly reduced differently by the tillage environments and soil amendments in the three years of study. It was observed that the interaction of the environments and amendments did positively (P<0.05) reduced the soil BD in the first and second year of study. The total porosity was also improved in the same periods of study in the location by the studied factors and their interactions. The mean weight diameter water retention (WR) and saturated hydraulic conductivity (Ksat) were also significantly improved upon in different forms by the factors and the interaction. The effects of tillage types and amendments were observed to have significantly (P<0.05) improved the rice grain yield.