Response of selected soil physical and hydrologic properties to manure amendment rates, levels, andtypes

Manure amendments affect several soil physical and hydrologic properties. The objectives of this study were to evaluate the effect of (i) manure amendment rates (0, 168, 336, and 672 kg total N ha), levels (one-time application, and two-time application), and types (chicken manure [CM], dairy manure [DM], and swine manure [SM]) on bulk density (ρb), total soil porosity (θt), and saturated hydraulic conductivity (Ksat) of a highly weathered tropical soil (Waialua gravely clay variant, isohyperthermic Pachic Haplustolls) and (ii) measuring instruments (tension infiltrometer [TI] and double-ring infiltrometers [DR]) on Ksat. For the two-time application level, all the plots received additional manure to compensate for the amounts decomposed during the first growing season. The field was tilled to the top 15-cm depth before and after manure application during the two growing seasons. Measurements of ρb and θt were conducted on undisturbed soil core samples collected from the top 10 cm of soil from a field cultivated with sweet corn (Zea mays L. subsp. mays) and irrigated with a drip irrigation system for two consecutive growing seasons. Saturated hydraulic conductivity was calculated from steady state infiltration rates measured with TI and DR. Results show that the increased manure amendment rates and levels significantly (P < 0.01) decreased ρb and consequently increased θt. The values of Ksat increased significantly (P < 0.01) with increase in CM and DM amendment rates and levels. For SM treatments, the values of Ksat decreased with increase in manure amendment rates and levels; these results concur with those reported in literature on liquid manures. Saturated hydraulic conductivity calculated from DR data was slightly greater than that from TI data for CM and DM treatments. Opposite results were found for SM treatments. However, a good agreement (R = 0.90) was observed between Ksat values calculated from TI and DR data across treatments. We conclude that the CM and DM amendments increased θt and Ksat and may also temporarily improve soil aggregation; however, SM amendments result in decreased Ksat. Thus, it is not recommended that slurry SM be applied to the soils with low hydraulic conductivity because it could further inhibit water infiltration and increase surface runoff and soil erosion.