Effects Of Sawah Water Management Systems On Soil Properties And Rice Grain Yield In Ebonyi State Southeastern Nigeria

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