TITLE:
A Single-Season Irrigated Rice Soil Presents Higher Iron Toxicity Risk in Tropical Savannah Valley Bottoms
AUTHORS:
Amadou Keita, Hamma Yacouba, Laszlo G. Hayde, Bart Schultz
KEYWORDS:
ANOVA; Burkina Faso; Hematite; Iron Toxicity; Rice; Soil Sampling; Tropical Savannah; Valley Bottoms; Welch T-Test
JOURNAL NAME:
Open Journal of Soil Science,
Vol.3 No.7,
November
25,
2013
ABSTRACT: With the aim of finding the
geochemical differences and helping to build alleviating strategies against
iron toxicity, two hematite dominant valley bottoms irrigating rice soils were
investigated in the Tropical Savannah region of Burkina Faso. The first site
was Tiefora, a 15-ha
modern double-season irrigated rice system and moderately affected by iron
toxicity (10% of the area with a toxicity score of 4). The second site was
Moussodougou, a 35-ha
traditional singleseason
irrigated rice valley-bottom, with 50% facing more severe iron toxicity (score
7). Nine soil extracts were taken from three depths—30, 50 and 100 cm—i.e. 27 at Tiefora and 27 at
Moussodogou. Five techniques were used to measure the data: 1) the ferrous iron concentration was
determined using a reflectometer, 2) a pH-meter yielded the pH, 3) clay-proportions were obtained by United States Department of
Agriculture (USDA) grain size analysis and densitometry, 4) the organic matter was determined by
oven drying (900℃) and v) the dry bulk density was determined by using
undisturbed soil samples. Statistical hypothesis testing of One-way ANOVA and
Welch t-test was applied to the data to isolate the similarities and the
differences between the two sites. A geochemical analysis followed to find the
causes of these differences. The results showed that while oxidation of pyrite
leads to a simultaneous increase in Fe2+ concentrations and acidity in the soils of
coastal floodplains and mangroves, the oxidation of hematite in Tropical
savannah valley
bottoms decreases Fe2+ but also increases acidity during the dry
season. As a consequence, it was found that the single-season irrigation scheme
Moussodougou is significantly (p-value 0.4%) more acidic (pH 5.7) than the double-season system of Tiefora (6.4) with also
750 - 1800 mg/l higher ferrous Fe2+.
The ferrous iron reached 3000 mg/l in some layers in Moussodougou. This result
is a justification to modernize a traditional single-season spate irrigation
schemes into a double-season irrigated rice scheme.