Drip fertigation : effects on water movement, soil characteristics and root distribution

[摘要] ENGLISH ABSTRACT:The application of water and nutrients via a drip irrigation system influences the waterdistribution in the soil, soil characteristics and root distribution beneath the dripper. Todetermine the water distribution pattern beneath a dripper in sandy soil, EnviroSCAN(Sentek) capacitance probes were installed directly below the dripper and at distances of20, 40 and 60 cm from the dripper. The continuous monitoring of the soil water content(SWC) beneath the dripper provided a good indication of how the water applied throughthe dripper is distributed in the soil. In this study a semi-impermeable layer in the soilwas detected through observing water accumulation patterns in the SWC. Wateraccumulated above the layer and SWC values increased to far above the upper level ofeasily available soil water (EAWupper),while the lower soil layers remained drier. Themeasurements also show that the horizontal water movement is restricted to 20 cm fromthe dripper. Specific parameters, such as the lower level of easily available soil water(EAWlower),can be used to determine optimal irrigation management. Together with thewater distribution study, the root distribution beneath a dripper was also investigated. Ahigh concentration of roots in the area beneath the dripper was found, whichcorresponds with the area wetted by irrigation.In another study, three irrigationlfertigation methods where investigated to ascertain theinfluence on soil characteristics and root distribution. These were: micro irrigation (MI)(micro-spinner irrigation with broadcast granular fertilization), conventional dripfertigation (CDF) (daily drip irrigation with daily or weekly fertigation with aunbalanced nutrient solution, containing macronutrients only) and daily drip fertigation(DDF) (daily fertigation of a balanced nutrient solution, containing macro- andmicronutrients). The study was conducted in two locations, viz. in the Western CapeProvince, on sandy soil, and in the Eastern Cape Province, on silt loam soil.Micro Irrigation: A wide and even root distribution in the entire wetted volume wasfound on the sandy and silt loam soil. On the sandy soil, the soil pH(KC1)directlybeneath the spinner was significantly lower than the pH(KC1)at positions further awayfrom the spinner.Conventional Drip Fertigation: Root studies on sandy soil indicate a poor rootdevelopment beneath the dripper, with a high concentration of roots in the area betweenthe drippers. The poor root development directly beneath the dipper may be due tooxygen deficiency and/or acidification beneath the dripper. The soil pH(KC1)valuesshow a significant lower pH(KC1)value directly beneath the dripper than further away. Incomparison to the sandy soil, the roots developed well beneath a dripper in a silt loamsoil. It appears as if soil acidity and/or oxygen deficiency was not a problem on this soiltype. The rest of the root system was also well developed. This may be due to thissoil's higher water holding capacity which creates a bigger wetted zone.Daily Drip Fertigation: In the sandy soil it seems that the roots developed in acontinuous column beneath the dripper line, with little root development further than20 cm from the dripper line. Where over-irrigation occurred, it caused a poor rootdevelopment directly beneath the dripper. The root density in this treatment was muchhigher than in the other two treatments. The use of a balanced nutrient solution andpulse irrigation may be reasons for the better root development. In a silt loam soil avery high concentration of roots was found beneath the dripper and the rest of the rootsystem was also well developed. As with the CDF treatment, it appears as if oxygendeficiency was not a problem on this soil type.

[发布机构] Stellenbosch University