Abstract:
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 inland valley at two different locations (Akaeze and Ikwo), to evaluate the effects of sawah water management systems on soil properties and rice grain yield. A split-split-plot in a randomized complete block design was used to evaluate these three factors (sawah types, growing environments and soil amendments) as they affect the soil properties of these two locations and the grain yield of rice as a test crop. Three sawah types and four rice growing environments were used in each of the two locations and they included; rain-fed sawah, spring type and pump type. The rice growing environments are; complete sawah- bunded, puddled and leveled rice field (CS); farmers environment- no bunding and leveling rice field (FE); incomplete sawah- bundding with minimum leveling and puddling rice field (ICS) and partial sawah- after bunding, no puddling and leveling rice field (PS). There were five levels of manure application, which were replicated three times and these 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 (2008, 2009 and 2010) using the same watershed and treatments. The treatments were applied annually, but the effects of additive residual effects of the amendments were not studied in the course of this research. At the end of each harvest, the soil physical properties analyzed for included; soil BD, total porosity, water stable aggregates, mean weight diameter, water retention and saturated hydraulic conductivity. While that of soil chemical properties included; soil pH, OC, total nitrogen, exchangeable bases (Na+, Ca2+, Mg2+ and K+). Others included CEC, exchangeable acidity, base saturation and available phosphorous, while the rice grain yields was measured. The results showed that the soil pH, organic carbon (OC) and total nitrogen (TN) were significantly improved by sawah types in all the studied soils. At Akaeze pH measured in water varied from 3.8 to 3.9, 4.3 to 4.5 and 4.5 to 4.6 in the first, second and third year (rain-fed to spring sawah type), respectively. The Ikwo soil showed pH mean values of 3.6 to 3.7, 4.4 to 4.6 and 4.6 to 4.8 in the 1st, 2nd and 3rd year of planting, ranging from rain-fed to spring sawah type, respectively. These parameters (pH, OC and TN) were also improved statistically upon by the different growing environments in different ways. The pH at Akaeze varied from 3.9 to 4.0, 4.2 to 4.4 and 4.5 to 4.8 in 1, 2 and 3rd year of study, ranging from farmers’ to complete sawah growing environment. The pH changed from 3.5 to 3.7, 4.3 to 4.6 and 4.5 to 4.9 within the three years of study and from farmers’ to complete sawah growing environment in Ikwo location. Also, the amendments equally positively influenced these parameters in the two locations. The SOC values in Akaeze location ranged from 1.05 to 1.14% (pumping to rain-fed) in the first year, 1.09 to 1.26% (pumping to spring sawah type) in the second year and 1.10 to 1.27% (pumping to spring sawah type) in the third year. In Ikwo location it ranged from 0.84 to 1.02% in the first year, 0.91 to 1.10% and 0.94 to 1.14% in the second and third year from rain-fed to spring sawah type, respectively. The exchangeable bases were also positively statistically influenced by these three factors tested and their interactions in both locations in most years of study. The results indicated that the CEC was positively improved by sawah types, growing environments and amendments in different forms in second and third years of study in both locations. The range values for growing environments in Akaeze varied positively (P<0.05) from 5.60 to6.31 cmolkg-1 for the 1st year, 5.44 to 10.70 cmolkg-1 (farmers’ to complete sawah environment), and 5.52 to 9.34 cmolkg-1 (farmers’ to complete sawah growing environment), in the 2nd and 3rd year, respectively. The mean values Ikwo location ranged from 9.56 to 10.89 cmolkg-1 in the 1st year, 10.17 to 12.73 cmolkg-1 and 10.61 to 13.24 cmolkg-1, in the 2nd and 3rd year, respectively. The results showed that poultry droppings significantly improved the CEC higher within the periods under study in the two locations. The mean values of CEC in Akaeze varied from 4.18 to 6.83 cmolkg-1, 3.92 to 10.86 cmolkg-1 and 3.78 to 9.15 cmolkg-1, in the 1st, 2nd and 3rd year of study. The mean values of CEC for the periods under study ranged from 7.36 to 11.27 cmolkg-1, 7.64 to 13.09 cmolkg-1 and 7.85 to 13.74 cmolkg-1 for the 1st, 2nd and 3rd year. The EA was also significantly reduced by these factors in both second and third years of study in Akaeze, whereas in Ikwo location, the soil EA was positively statistically reduced by these factors for the three years of study. The EA on the 3rd year varied from 2.39 to 2.99 cmolkg-1, (complete to farmers’ growing environment) in Ikwo soils, while in Akaeze, it varied from 2.99 to 3.07 cmolkg-1, (partial to complete growing sawah growing environment) on the same 3rd year of study. The available phosphorous was significantly improved by these three factors and their various interaction forms in both second and third year of study in the two locations. In the same manner, the base saturation was affected in most years of study by the studied factors and their various forms of interactions. The soil bulk density (BD) was significantly reduced differently by sawah types; growing environments and soil amendments in both sites in the three years of study. It was observed that the interactions of sawah types and growing environments; sawah types, growing environments and amendments did positively (P<0.05) reduced the soil BD of Ikwo soils for the second and third year period of study, while in Akaeze site, it was the interaction of sawah types and growing environments only that did positively reduce the soil BD in the first and second year of study. The total porosity was also improved in the same periods of study in both locations by the studied three factors and their interactions. The water stable aggregate (WSA), water retention (WR) and saturated hydraulic conductivity (Ksat) were also significantly improved upon in different forms by the three factors and their various forms of interactions. The effects of sawah water types was observed to have significantly (P<0.05) improved the rice grain yield. The mean grain yield values in Akaeze ranged from 2.87 – 3.54 t/ha, in the first year, 3.63 – 4.03 t/ha in the second year and 4.23- 5.00 t/ha in the third year of planting. The mean grain yield values in Ikwo varied positively (P<0.05) from 3.38 – 3.73 t/ha in the first year, 5.12 – 5.67 t/ha in the second year and 5.39 – 6.28 t/ha in the third year of planting with the spring sawah type yielding higher. It was also obtained that all the sawah growing environments positively improved the grain yield relatively higher than the farmers’ growing environment. The mean values in Akaeze varied positively (P< 0.05) from 2.55 – 3.92 t/ha, 3.16 – 4.46 t/ha and 4.03 – 5.00 t/ha in the 1st, 2nd and 3rd year of planting, respectively. In Ikwo site, it ranged from 3.19 – 3.84 t/ha, 4.84 – 5.86 t/ha and 5.28 – 5.94 t/ha in the first, second and third year of planting, respectively, with complete giving higher yield in both locations than other environments. It was generally observed that plots amended with poultry dropping significantly (P< 0.05) increased the grain yield in both locations in the whole three years of the study. The results from Akaeze location showed the range mean values of the rice as; 1.71 to 4.04 t/ha in the first year, 1.61 to 4.59 t/ha in the second year and 1.78 to 5.52 t/ha in the third year of planting. Also in Ikwo location, the values varied from 1.87 – 4.12 t/ha, 1.98 – 6.78 t/ha and 2.09 – 6.75 t/ha in the 1st, 2nd and 3rd year of planting, respectively. The combination of sawah management and amendment practices improved the soil properties and rice grain yield significantly (p < 0.05) in most of the years in both locations.
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