|Novak, Jeffrey - Jeff|
Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2007
Publication Date: 8/17/2007
Citation: Busscher, W.J., Novak, J.M., Caesar, T., Sojka, R.E. 2007. Amendments to increase aggregation in United States southeastern Coastal Plain soils. Soil Science. 172(8):651-658. Interpretive Summary: Because SE Coastal Plain sandy soils hold little water and harden to root-restricting strengths as they dry, they cannot provide adequate water for unstressed plant growth. Soils can provide more water to the plant if they are deep tilled which allows roots to penetrate hard layers; but tillage is expensive, especially as fuel costs increase. To reduce soil hardness and improve its ability to provide plant water without tillage, soil was amended in a lab experiment with wheat residue and polyacrylamide (PAM). Amendments included a large amount of field residue (the equivalent of 6.5 tons/acre) and a small amount of PAM (either 60 or 240 lbs/acre); duplicate sets of treatments were incubated at 10% water content for 30 days and 60 days. Amendments of wheat residue, the higher rate of PAM, and the mixture of the two increased soil water holding and decreased soil strength, especially when treatments were allowed to incubate for 60 days. Although rates of amendment and mixtures of organic matter and PAM still need to be refined and their mechanism needs to be better understood, they can reduce the need for deep tillage and provide more water to the plant in these hard, sandy soils.
Technical Abstract: Many southeastern Coastal Plain soils have a cemented subsurface hard layer that restricts root growth into the subsoil and decreases productivity. Soil properties are usually improved by tillage but might also be improved by amending the soil. Wheat (Triticum aestivum L.) residue and polyacrylamide (PAM) amendments were mixed into a Norfolk soil mix of 90% E horizon (the hard layer) and 10% Ap horizon; the latter was added to assure microbial presence. Our hypothesis was that incorporation of wheat residue and/or PAM would improve soil physical properties, making the soil more amenable to root growth. Treatments contained 450 g of soil mix, 6.44 g/kg ground wheat stubble, and 0, 30, or 120 PPM of PAM; duplicate sets of treatments were incubated at 10% gravimetric water content for 30 d and 60 d. Treatments were leached with 1.3 pore volumes of water. After leaching and equilibration to stable water contents, soil strengths were measured with a 3-mm-diameter flat-tipped bench-top penetrometer. At 30 d, the treatments did not appear to be effective; but at 60 d, treatments differed. A PAM formulation of 12 Mg/mole molecules, anionic, and 35% charge density decreased bulk density when added at the higher rate of 120 PPM to the soil. The higher PAM rate also decreased the amount of water that was added to maintain treatments at 10% water content. Wheat amendments decreased penetration resistances and increased aggregation. Amendments improved soil physical properties, especially when soils were amended with 120 PPM PAM and when treatments were allowed to incubate for 60 d.