Effects of coarse fragment content on soil physical properties, soil erosion and potato production

Abstract

Most potato (Solanum tuberosum L.) production in northeastern America is on till soils with an abundance of stones. Stone picking has removed many coarse fragments to a point that it might be detrimental to soil quality. This study was to assess the impacts of coarse fragment content (10–19 mm in diameter) on selected soil physical properties, field soil thermal and water regimes, runoff and soil loss and potato yield and tuber quality on a sandy loam soil in New Brunswick. The objectives were to evaluate both beneficial and adverse effects of coarse fragment content (0, 10, 20 and 30% by volume) on soil quality in relation to potato production over a 4-yr period. Soil bulk density increased significantly by incorporating 10 to 30% coarse fragments into the plow layer. Porosity and available soil water-holding capacity were reduced in response to this increase in bulk density. In spite of the reduction in total porosity, pore size greater than 148 µm diameter of the 30% coarse fragment treatment was significantly greater than the 0, 10 and 20% treatments during 2001, 1 yr after the treatments were applied. This increase in macropores may have been responsible for the significantly higher saturated hydraulic conductivity of the soil treated with 30% coarse fragments. The results from 2002 and 2003 show that these beneficial effects on soil physical properties were short lived in this study; however, this may not be the case under field conditions because experimental plot problems of relocation of coarse fragments beyond plot boundaries and/or dilution with incorporation of stone-free subsoil material is not an issue in the field. Volumetric water content at field capacity of −33.3 kPa matric potential declined from 20.9% for the control to 7.7% for the 30% coarse fragment treatment. Cumulative soil heat greater than 10°C of the 30% treatment showed significant increases of 11.2, 8.8, and 3.7% during the growing season of 2001, 2002, and 2003, respectively, as compared with the control. Although field soil water tension regimes revealed that soil water in different treatments was held at a somewhat similar energy status, field soil water content was reduced considerably with increasing amount of coarse fragments. No significant differences in runoff and soil loss were found between treatments, but average reductions in soil loss over the 3-yr period were 9, 36, and 47% lower than the control for the 10, 20, and 30% treatments, respectively. Although no significant difference in yield and tuber quality between treatments was found in 2001–2003, both total and marketable yield decreased with increasing time. The yield reduction over time may be directly attributed to the mono-culture of potatoes practiced during the course of this experiment. Key words: Soil temperature, soil moisture, conductivity, bulk density, tillage erosion, potato cropping