Assessing the impact of organic versus conventional agricultural management on soil hydraulic properties in a long‐term experiment

Abstract

Investigating the effects of various agricultural management systems on soil hydraulic properties in long‐term field experiments allows farmers to evaluate their efficacy in mitigating the effects of droughts and floods, which are expected to intensify in the coming decades. This study's main objective was to quantify soil structural and hydraulic properties in plots under organic manure, organic leguminous, and conventional agricultural management and related tillage practices at Rodale Institute's Farming Systems Trial. Soil cores were collected at depths of 0–10, 10–20, and 20–30 cm and analyzed for soil water retention, saturated hydraulic conductivity (Ksat), soil organic C (SOC), bulk density, and particle size distribution. Management practices had a measurable effect on SOC and bulk density, but not on Ksat, the parameters of the soil water retention model (rm and σ), or the calculated indicator water content values: field capacity (θfc), wilting point (θwp), plant available water (θpaw), and air capacity (θAirCap). Tillage practices (no‐tillage vs. tillage) had a measurable effect on SOC, bulk density and θAirCap, but not on Ksat, θfc, θwp, or θpaw. Significant differences by depth were observed for θfc, θwp, θpaw, θAirCap, SOC, and bulk density, but not for Ksat. Our results suggest that relatively minor differences between management practices may be insufficient for generating quantifiable differences in soil structure, and more substantial changes to management practices will be necessary to achieve the outcomes for developing climate‐resilient agricultural soils.

Do organic farming practices improve soil physical properties?

“…Indeed, Table S7 shows that OF, when it increased K sat , also increased soil organic C concentration in most cases. OF increased soil organic C concentration by 1.2-3.2 times compared with CF (Table S7), which indicates a large impact of OF on soil C. However, in some cases, OF may not increase K sat even with increases in SOC concentration (Alfahham et al, 2021;Williams et al, 2017). The use of tillage for OF may reduce soil macroporosity, which may eliminate the positive effects of OF on K sat .…”

“…Soil hydraulic properties determine the ability of the soil to transmit and retain water (Alfahham et al., 2021; Williams et al., 2017). Some of the relevant hydraulic properties include water infiltration, saturated and unsaturated hydraulic conductivity, water retention, available water content, and water repellency.…”

“…Even large additions of organic amendments and long‐term OF management do not seem to alter K unsat under OF. For instance, a 40‐year study at the Rodale Institute in Pennsylvania, U.S., found two OF rotations with cover crops (cereal rye and hairy vetch) with and without composted animal manure (33.6 Mg ha −1 applied every 2 or 3 years) increased soil organic C concentration and reduced soil bulk density but did not alter soil hydraulic conductivity (Alfahham et al., 2021). Also, a study across 114 soils in southern Spain reported OF had mixed effects on K unsat (Parras‐Alcantara & Lozano‐Garcia., 2014).…”

“…The few studies on unsaturated hydraulic conductivity ( K unsat ) found that OF does not generally alter this parameter compared with CF (Alfahham et al., 2021; Parras‐Alcantara & Lozano‐Garcia., 2014). The limited or no effect of OF on K unsat is not surprising as this soil property is not as sensitive to management shift as K sat and other hydraulic properties.…”

“…While some individual studies on OF have found positive effects of OF on soil physical properties (Williams et al., 2017), others have found that these impacts of OF can be mixed, depending on OF management (i.e. amendment type, years under OF), soil properties, and others (Alfahham et al., 2021; Papadopoulos et al., 2014). We need to better understand how OF affects soil physical properties.…”