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Evaluation of Simulated Seedling Emergence through Rainfall Induced Soil Crusts¹

ABSTRACT

Extensive areas of cultivated soil throughout the world develop rainfall-induced crusts which impede seedling emergence. Quantitative information is needed on the factors influencing the development of crusts and on the influence of ameliorating treatments on crust strength. A convenient method was developed to make impedance measurements. Soil was placed in boxes which were equipped with guided tubes to allow a probe (simulated seedling) to penetrate the soil crust from below. Measurements were made by means of a balance which supported the probe, as it was raised by means of a jack.

The equipment was used to collect data on the relationship between rainfall intensity and soil crust impedance. Simulated rainfall of intensities from 1.3 to 5.1 cm/hour and durations of 19 to 60 min were used to form the crusts. Determinations of crust impedance were made daily for 7 days with a 12-hour drying cycle.

For the loam soil tested, the maximum daily average impedances were 1,766, 2,226 and 1,851 g of force for rainfall intensities of 1.3, 2.5, and 5.1 cm/hour respectively. Crust impedance for all tests increased initially as the soil dried, then declined as cracking increased.

An inverse relation was found between mechanical impedance and the percent crust moisture between 20 and 2.8% moisture; the maximum impedance occurred in the narrow range of 2.8 to 2.2% moisture. An increase in the coefficient of variability as the soil dried was associated with cracking. Different durations of rainfall at similar intensities resulted in larger differences in impedance than did different intensities for the same duration.

¹ Contribution from the Texas Agricultural Experiment Station, College Station 77843.

² Graduate Student and Assistant Professor, Soil and Crop Sci. Dep.

Received for publication February 6, 1974. Accepted for publication May 28, 1974.