Contour ripping is more beneficial than composted manure for restoring degraded rangelands in Central Texas

Abstract

Rangelands in the United States that have been the site of military training exercises have suffered extensive ecological damage, largely because of soil compaction, creation of ruts, and damage to or destruction of vegetation—all of which lead to higher runoff and accelerated erosion. In this paper we report on a study carried out within the Fort Hood Military Reservation in Central Texas, where we evaluated the extent to which application of composted dairy manure and contour ripping affect soil infiltrability, amount of runoff, and nutrient concentrations in runoff. We conducted experiments at two locations, using rainfall simulation at one and monitoring discharge from small (0.3-ha) watersheds at the other. At the rainfall simulation site, we used six levels of compost application: 4, 8, 12, 16, 20, and 24 Mg/ha. We found that compost application had little effect on runoff, soil infiltration, sediment production, or nutrient concentrations in the runoff—except at the micro-watershed scale (12 and 24 Mg/ha); in this case, nutrient concentrations in runoff were initially high (for the rainfall simulations done immediately after compost application). In contrast, contour ripping—carried out 22 months after compost application on two of the micro-watersheds—was highly effective: runoff on the treated micro-watershed was reduced by half compared with the untreated micro-watershed. Our results suggest that (1) one-time applications of composted dairy manure do little to enhance infiltration of degraded rangelands over the short term (at the same time, these experiments demonstrated that compost application poses very little risk to water quality); and (2) for degraded rangelands with limited infiltration capacity, contour ripping is an effective strategy for increasing infiltration rates.