Biochemical Properties of Decomposing Cotton and Corn Stem and Root Residues

residues (Franzluebbers et al., 1994; Rovira and Vallejo, 2002). Maintaining soil C is especially difficult in hot climates. Information Soil C decomposition and retention also depend on is needed regarding the influence of residue biochemical properties residue biochemical quality (Melillo et al., 1982; Heal on decomposition in hot, semiarid climates so that management pracet al., 1997; Seneviratne, 2000), soil factors (Alvarez and tices can be developed that improve organic matter retention. Litterbags containing stalk or root tissues of senescent cotton (GosLavado, 1998; Bayer et al., 2001) and on the environsypium hirsutum L.) or corn (Zea mays L.) were placed on the surface mental conditions (Meentemeyer, 1978) under which or 10 cm below the surface of a fallow Hidalgo sandy clay loam (finethe residues are decomposed by microorganisms. Both loamy, mixed, hyperthermic Typic Calciustoll) near Weslaco, TX, USA residue placement and quality contribute to stratifica(26 9 N lat., 97 57 W long.), and were monitored quarterly for 1 yr tion and accumulation of C and nutrients in reducedfor changes in mass, water-extractable C (WEC), waterand alcoholtillage soils. extractable polyphenolics (WEP and AEP, respectively). SurfaceRelatively little is understood about relative C inputs placed cotton residues retained more mass than when buried, from to soil from roots and shoots (Gale and Cambardella, approximately 80% (surface) to 50% (buried). For corn, retention 2000), and little is known specifically about the contriburanged from approximately 60 to approximately 70% for surface resition of roots to soil C (Soon and Arshad, 2002). Preservdues to approximately 40% for buried residues. Most mass loss occurred within the first three months. The greatest increases in WEC ing crop residues where they are physically produced (approximately 1500 g C g 1 for corn; approximately 500 g C g 1 (i.e., shoots above ground, roots below ground) further for cotton) and WEP (approximately 175–325 g g 1) for corn also differentiates inputs based on residue quality compared occurred within the first 3 months. Water-extractable polyphenolics with the mixing of residues and soil during tillage. peaked (about 100 g g 1) in cotton residues at 6 mo, while corn resiRoots dominate organic matter inputs to the upper dues reached a maximum (approximately 300 g g 1) at 3 months. soil horizons while aboveground residues provide the surOver a year, AEP decreased in cotton stem residues, from approxface inputs in no-till systems. Carbon inputs from roots imately 5 to 8 to approximately 2 g g 1. Surface cotton roots maincan be substantially different from that of shoots (Puget tained approximately 6 g g 1 after three months. Results illustrated and Drinkwater, 2001) resulting in different decompothe importance of residue moisture content during decomposition, sition and nutrient mineralization patterns. Gale and and indicate that different residues may have different capacities to hold moisture, which may affect the biochemical characteristics and Cambardella (2000) concluded that root-derived C was kinetics of decomposition. more responsible than surface residue-derived C for soil C gains in a no-till soil. The influence of roots on SOM transformations may be greater than that of aboveground S organic matter (SOM) content is an important residues (Milchunas et al., 1985; Norby and Cotrufo, 1998). factor in the long-term sustainability of agricultural Plant polyphenolics are important factors in C and N production systems. Many agricultural practices, such transformations and nutrient fluxes in soil (Palm and as intensive tillage and crop residue removal, promote Sanchez, 1990; Martens, 2002), and play an important role soil C loss. Reduced tillage (Bayer et al., 2001; Zibilske in aggregate stability (Martens, 2002). Residues high in liget al., 2002) and the conservation of crop residues often nin and polyphenols tend to extend C residence time in slow or reverse C losses compared with conventional soils (Tian et al., 1993). Using crop residues high in polyagronomic practices (Kern and Johnson, 1993). Conserphenolic content may encourage C retention (Tian and vation tillage maintains crop residues on the soil surface, Brussard, 1997) and counteract the more rapid SOM reduces soil mixing and stratifies SOM inputs and conselosses in tropical climates (Sanchez and Logan, 1992; quent nutrient mineralization (Unger, 1991) and SOM Shang and Tiessen, 1998; Jenkinson and Anayaba, 1977). accumulation (Blevins et al., 1984). Residues on the soil Soil pH has been found an important factor in the solsurface decompose more slowly than buried residues ubility of phenolic acids (Whitehead et al., 1983). White(Douglas et al., 1980) due in part to greater exposure to head et al. (1981) found that water-extractability of phenolic acids increased with increasing pH, with the extremes in moisture availability compared with buried solubility threshold between pH 7.5 and 10.5. However, in a review of N release patterns from a broad range of L.M. Zibilske, USDA-ARS, Integrated Farming and Natural Replant litters and leaves in tropical systems, Seneviratne sources Research Unit, 2413 E. Hwy 83, Weslaco, TX 78596-8344. (2000) found that all of the reviewed studies were conL.A. Materon, The Univ. of Texas-Pan American, Biology Dep., 1202 ducted in soils with pH ranges from 4.5 to 6.5. This inWest University Drive, Edinburg, TX 78539. Mention of trade names or commercial products in this article is solely for providing specific dicates a lack of information regarding the relationships information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. Received 16 Feb. 2004. *CorreAbbreviations: AEP, alcohol-extractable polyphenolics; DOM, dissponding author ([email protected]). solved organic matter; SOM, soil organic matter; WEC, water-extractable organic C; WEP, water-extractable polyphenolics; *, significant Published in Soil Sci. Soc. Am. J. 69:378–386 (2005). © Soil Science Society of America at the 0.05 probability level; **, significant at the 0.01 probability level; ***, significant at the 0.001 probability level. 677 S. Segoe Rd., Madison, WI 53711 USA