The effect of different furrow irrigation regimes on infiltration and sugarcane (Saccharum officinarum L.) yield at Ubombo Swaziland.
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Date
2003
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Abstract
In surface irrigation, the soil serves as a medium for infiltration and for conveying water
from the upstream to the downstream end of a field. Soil infiltration characteristics are
therefore extremely important for surface irrigation design and management. In this
study, the infiltration characteristics of the Sibaya (Si) soil type (Glenrosa, in the South
African soil classification system) was determined by a volume balance method using a
two-point approach technique. The infiltration model adopted was that of Kostiakov. The
purpose of the study was to examine the effect of different irrigation scheduling on
infiltration characteristics, and on irrigation performance. A trial was conducted on a field
with predominately Rondspring and Sibaya soils from 1999 to 2001. The five irrigation
treatments were the Ubombo method, Penman-Monteith (PM) derived irrigation
scheduling factors of 1.25, 1.00 and 0.75, and alternate row irrigation using Ubombo
scheduling and 1.00 x PM on plant and first ratoon cane, respectively. Treatments were
arranged in a randomised complete block design with five replication. The Ubombo
scheduling method had the highest number of irrigation events followed by the 1.25 x
PM, whilst the 0.75 x PM had the least. The infiltration variables indicated that, for the
Ubombo and 1.25 x PM treatments, irrigation often occurred when the soil water content
was still less than 50% depleted plant available water (DPAW). This was in agreement
with the tensiometer and neutron probe data. The tensiometer readings ranged from -55
to -75 kPa, -50 to -65 kPa, and -8 to -12 kPa at 0.15 m, 0.30 m, 0.45 m soil depth
respectively. Likewise, 0.75 x PM was irrigated when the soil water content was greater
than 50% (DPAW). Tensiometer readings would nearly always read above -80 kPa at
both 0.15 m and 0.30 m, and above -75 kPa at 0.45 m. Further examination of the
tensiometer and neutron probe data suggested that irrigation scheduling determined the
preferential depth of water uptake by the crop. Frequent irrigation resulted in the crop
depleting soil water predominately at the 0.15-0.30 m soil depth and hardly any at 0.45 m
and below, particularly when the crop was young. There were no significant differences
in yield among any of the treatments in the plant or ratoon crops. The plant crop
consistently recorded higher yields than the first ratoon in all the treatments. Ubombo
scheduling recorded the highest sugarcane yield in both seasons at 84 tha(-1) for the plant
and 82 tha(-1) for the first ratoon cane. The 0.75 x PM had the lowest yield (78.3 tha(-1)) in
the plant crop as well as in the first ratoon (74 tha(-1)). The volume balance approach
provided a reliable and convenient way of assessing surface inigation systems to identify
alternatives that may be effective in improving the system performance, and in assessing
different irrigation schedules. Sound management which comes about by selecting the
most efficient stream size, length of field, and set time, and also a suitable irrigation
schedule for that soil type depends on detailed knowledge of the infiltration rate of a
particular soil. Information on infiltration constitutes the basis for establishing the
necessary design, evaluation criteria and operational management system in irrigation.
Description
Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 2003.
Keywords
Sugarcane--Irrigation--Swaziland., Furrow irrigation--Swaziland., Sugarcane--Yields--Swaziland., Soil infiltration rate--Measurement., Theses--Crop science.