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Migration of Salt from Feedlot Waste as Affected by Moisture Regime and Aggregate Size¹

ABSTRACT

The migration of salt from three different aggregate sizes of feedlot manure under three moisture regimes was evaluated. The three sizes were small (to pass a 40-mesh sieve), medium (0.9 cm in diameter, 2.25 cm in length), and large (4.8 cm in diameter, 2.6 cm in length). The three moisture regimes were: (i) 12 hours saturation, 12 hours drainage by gravity, this step was repeated five times; (ii) 12 hours saturation, 12 hours drainage by gravity, 48 hours oven drying at 60C, also repeated five times; and (iii) continuous leaching for 60 hours at a constant rate. After each 12- hour saturation period the leachates were collected and the electrical conductivity (EC), pH, and concentrations of K, Na, Ca, Mg, NH₄, NO₃, Cl, S, P, and eight trace elements determined.

The EC of the leachate for the first saturation period was highest for the small-sized aggregates under all three moisture regimes (21.3, 21.2, and 19.3 mmhos/cm, respectively) and the lowest for the large-sized aggregates under continuous leaching (8.3 mmhos/cm). During the later leaching periods, the EC of the leachate for the large aggregates was higher than the other two sizes. Continuous leaching resulted in a lower EC for the first and a greater EC for the later saturation periods compared to the other two treatments. As for the individual salts, the migration pattern for K, Na, S, and Cl was similar to that for EC, however, the pattern for the other ions was dissimilar.

Key Words: salinity • water management • manure disposal

¹ Arizona Agric. Exp. Sta. Paper No. 2364. This research was supported in part by funds from the Regional Research Technical Project W-124.

² Graduate Assistant, Professor, and Associate Professor, Department of Soils, Water & Eng., The University of Arizona, Tucson, AZ 85721.

Received for publication November 14, 1974.