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The Effect of Stabilized, Hydrophobic Aggregate Layer Properties on Soil Water Regime and Seedling Emergence¹

ABSTRACT

Soil crusts affect both the profile water regime and the fate of crop seedlings. The former is affected via modification of infiltration, evaporation, and redistribution, while mechanical crust impedance prevents or retards seedling emergence. Growers alleviate this problem by frequent, small irrigations which are costly in water, equipment, and labor. This study was conducted to determine whether surface soil properties could be modified by layers of stabilized, hydrophobic aggregates so as to render these irrigations unnecessary.

Unstable aggregates of a clay-loam soil were treated with 7% potassium siliconate and 1% polyvinyl acetate based on dry-weight of soil and sprayed in water to wet the soil to 15% gravimetric water content. Layers of soil mixes with different aggregate-size distribution were placed in transparent columns and given a simulated rainfall; then the progress of infiltration, redistribution, and drying was followed. The most promising mix was used in large outdoor tanks as a mulch for carrots (Daucus carotta L.), using 1- and 4-cm mulch layers with 0, 25, 50, and 100% cover of the soil surface. The soil was given one post-sowing sprinkler irrigation, and the soil moisture regime was monitored by microtensiometers and a two-probe gamma gauge.

A 100% cover of 4-cm deep mulch of treated aggregates was the most effective for water conservation. It decreased water loss by 20% over a 14-day period. Seedling emergence was close to 90% under a 1-cm mulch and 50% under a 4-cm layer, both of which were superior to the unmulched control treatment.

¹ Contribution from the Dep. of Soil & Water Science, Hebrew Univ. of Jerusalem, Faculty of Agric., Rehovot, 76 100, Israel. Supported in part by the joint Holland-Israel project on Soil Management and Tillage Operations.

² Senior Lecturer and Graduate Assistant, respecively, at the Faculty of Agric., Rehovot, Israel.

Received for publication December 14, 1977. Accepted for publication May 8, 1978.