Long-Term Effect of Different Carbon Management Strategies on Water Flow and Related Processes for Three Loamy Soils

Abstract

The decline in organic matter of arable land, induced and accelerated by modern agriculture, has been identified as a threat to sustained soil quality. In this article, we studied strategies to counter this decrease by building up soil organic carbon (SOC) levels in the soils using several approaches. They included return of organic matter, such as straw, animal manure, and slurry, to the soil and diverse crop rotations with, for example, grass-clover leys. We used three field sites in Denmark with different C repletion strategies to assess and quantify the effect of these approaches on preferential flow and loss of colloids during heavy irrigation events. The field sites were all under long-term management and therefore represent up to 30 years of pairwise different management strategies. One field in each field pair was managed with a more C-repleting strategy (HighC) than the other (LowC). Only small differences in SOC contents were identified, and none of the management strategies had succeeded in building up SOC pools large enough to saturate the soil with C. Only at one field site was the content of water-dispersible colloids lower in the HighC than the LowC treatment. Preferential flow patterns showed a rapid breakthrough of irrigation water but only little or negligible effect in reducing the risk of colloid loss and chemicals leaching from the root zone, despite 20 to 30 years of different management strategies with this aim. Previous studies reported in the literature have emphasized high SOC contents and grass ley soils to significantly reduce nonequilibrium water flow. Our results thus indicate the need for more effective management options than those addressed in this study.Mean values based on four replicate blocks (R) or nine grid subsamples. ** and *** represent a statistical difference with P < 0.01and P < 0.001, respectively, between the two sites in each location.Vendelboe et al.

Long‐term Effects of Organic Waste Fertilizers on Soil Structure, Tracer Transport, and Leaching of Colloids

“…However, the difference in the shape of the EC curves (i.e., the later peak in EC) might be seen as an indication that the CMA and CHA treatments exhibit a larger degree of lateral mass transfer compared with the U, CS, and SA treatments. Previous studies analyzing relations between either SOM or clay/OC (Dexter) ratio and 5% mass recovery of 3 H 2 O at free drainage conditions did not find significant correlations between the soil C parameters and early tracer breakthrough Soares et al, 2015;Vendelboe et al, 2013). This is in accordance with the present study in which a wide range in the clay/OC ratio did not affect either early tracer breakthrough or mass recovery in general.…”

Preferential Transport in Macropores is Reduced by Soil Organic Carbon

“…However, the effects of SOC per se on solute transport in arable soil have hardly been investigated and are not well understood. The results from two earlier studies that attempted to address this question were inconclusive (Vendelboe et al, 2013; Soares et al, 2015), probably because the range of variation in SOC content (17–22 g kg −1 ) was too small. Other studies performed at the field and catchment scales for a limited number of soil columns have suggested that preferential transport may be weaker in conventionally tilled arable topsoils with larger SOC content (Jarvis et al, 2007; Ghafoor et al, 2013; Paradelo et al, 2016).…”

When does the fluazifop-P-butyl degradate, TFMP, leach through an agricultural loamy soil to groundwater?

“…Preferential flow can occur readily during both near-saturated and unsaturated conditions (e.g. de Jonge et al, 2004;Rosenbom et al, 2008;Vendelboe et al, 2013), allowing water to bypass the soil matrix and its retarding effect (degradation and sorption), and providing a direct pathway to drainage and groundwater (Jarvis, 2007), which may increase leaching of pesticides and their degradation products, such as TFMP. Kjaer et al (2005) found preferential flow occurring within a short time of application of glyphosate to be the governing factor for glyphosate leaching, and Rosenbom et al (2014) found that MCPA only leaches out of the root zone if preferential flow occurs.…”