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The use of polyvinyl alcohol to improve emergence of vegetable crops grown on fine textured Goulburn Valley soils

C. Hunter, I. Wilson and R. Greene

Irrigation Research Institute, Tatura. Vic. 3616.

Fine textured soils in the Goulburn Valley of Victoria are prone to slaking as a result of high intensity droplet impact from rain and sprinklers. If this occurs after sowing and prior to seedling emergence a strong crust forms on drying which reduces crop establishment. Soil conditioners, such as polyvinyl alcohol (PVA) have been used successfully with wheat to prevent crust formation. Their use already appears to be economical with high return vegetable crops. The aim of this work was firstly. to determine if PVA could be used successfully on Goulburn Valley soils, and secondly, to establish the criteria for applying PVA economically under a range of known field conditions.

The methods used were:- (1) Emergence counts on field plots of 1 m2 sown with a range of different vegetables. Plots were irrigated to approximately field capacity (20% moisture content) and a 1% PVA solution (MW 110,000) incorporated to a depth of 20 mm, so as the final concentration was 0.2 g PVA per 100 g soil. All plots were then irrigated with knocker sprinklers (5 mm h-1) which produce large droplets. (2) Measurement of the saturated hydraulic conductivity Ks of cores of PVA treated aggregates. 2-6 mm aggregates were sprayed with 1% PVA solutions when either air-dry. or at 20% moisture content, so that the final concentration was 0.2 g PVA per 100 g soil. They were then packed into perspex rings, 12 cm diameter, 6 cm high and subjected to 35 mm h-1 of simulated rain.

TABLE 1. % emergence for a range of different vegetables.

TABLE 2. Saturated hydraulic conductivity of cores of PVA treated aggregates.

The emergence counts showed that PVA significantly improved emergence compared with the control (Table 1). Seedlings such as beet which in this experiment emerged quickly showed no improvement in establishment. It is believed the slaked surface had insufficient time to produce a consolidated crust to prevent emergence. The Ks measurements indicated that the aggregates were most stable when they had been wet to 20% moisture content and then sprayed with PVA MW 110,000 (Table 2).

The results clearly show that PVA will effectively stabilize fine textured Goulburn Valley soils against slaking. The most effective method of achieving this is to spray moist aggregates with PVA MW 110,000. Further investigations studying a larger range of seed bed moisture conditions, different application rates and different molecular weight polymers are proceeding before routine application of soil conditioners can proceed on a large commercial scale.

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