Quantcast Irrigation System Furrow Improvements (cont.)

 
  
 
Sod furrows were shown by Cary (1986) to nearly eliminate erosion, but mowing was
required. Berg and Carter (1980) found that seeding crops in furrows was effective in reducing
erosion.
Much of the sediment lost from irrigated fields occurs in the last few meters of the furrow
(Carter and Berg 1983). Tailwater ditches should be kept shallow to avoid a severe gradient and
associated increased scour and erosion. Tailwater ditches are often kept well cleaned and below the
level of the end of the furrow to remove tailwater rapidly, but this practice erodes furrow ends and
creates convex-shaped fields. To remedy the problem and to increase the productive area of the field,
Carter and Berg (1983) developed a buried pipe system with riser inlets to drain fields and trap up to
80 to 95% of the sediment in runoff.
Tailwater pollutant control devices include collection ditches, buffers or sediment traps.
Efficiency is high for these structural BMPs but they are subject to failure and require maintenance.
Concrete collection basins may reduce sedimentation by 25% (Brockway 1986). Mini-basins and I-
slots can trap up to 86% of the sediment from irrigated furrows. Efficiency for sediment basins has been
reported as 66% with a range of 53 to 85% by King et al. (1984). Carter and Berg (1983) report a
87% efficiency with a range of 75-90% sediment trapped. Sediment traps require cleaning to maintain
high levels of efficiency. King et al. (1984) found 51% phosphorus trapping efficiency for sediment
basins. The lower trapping efficiency compared to sediment is thought to be due to was lower settling
velocity and subsequent flow-through of phosphorus attached to clay sized particles .
Nitrogen content of irrigation water can have an affect on dissolved nitrogen concentration in
surface irrigation return flows. Carter et al. (1971) found that nitrogen concentration did not increase
appreciably as water passed over the soil surface. Fitzsimmons et al. (1972), Carlile (1972), and
Naylor and Busch (1973), also found little difference between dissolved nitrogen in irrigation and return
flow waters. However, when soluble nitrogen is added to irrigation water or when liquid nitrogen is
applied, increases in return flow concentrations can be expected (Carter and Bondurant 1976) and
runoff losses may be proportional to the amount applied (Naylor et al. 1972).
Nitrogen concentrations may be higher when irrigation water makes contact with decaying plant
material. Higher organic nitrogen losses may be attributable to runoff losses of organic matter and
sediment (Carter and Bondurant 1976).
Water management practices have a significant impact on runoff, nutrient losses and farm
productivity. Numerous power functions have been fit to the relation between runoff water applied
(stream size) to erosion. McNeal et al. (1982) found that runoff volume raised to the second power
gave a reasonable estimate of erosion. GMC Neal et al. (1982) summarize the combined effects of
slope and runoff water applied on sediment loss.
4.2-13

 


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