BIOCHEMICAL PROPERTIES OF DECOMPOSING COTTON AND CORN STEM AND ROOT RESIDUES

Authors: Zibilske, Larry; MATERON, LUIS - UNIV. OR TX-PAN AMERICAN

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2004
Publication Date: 3/1/2005
Citation: Zibilske, L.M., Materon, L.A. 2005. Biochemical properties of decomposing cotton and corn stem and root residues. Soil Science Society of America Journal. 69:375-386.

Interpretive Summary: Keeping soil organic matter high is beneficial to crop production. In hot climates, soil organic matter is broken down so rapidly that it becomes deficient in many soils. We need to know more about the effects of conservation tillage on organic matter retention in soils, especially in hot climates, so that management practices that improve organic matter retention can be developed. In this experiment, bags containing stalk or root tissues of cotton or corn were placed on the surface or below the surface of the soil, and were followed for one year to determine the kind of changes that happen to the chemistry of the plant parts. Cotton plants left on the surface did not decompose as rapidly as did those that were buried; 80% remained of those on the surface compared to less than 50% when buried. For corn, the same numbers were 65% and 40%. Most of the reduction in plant bulk occurred within 3 months. Carbon in solution is one measure of breakdown rate. The highest soluble carbon in corn was 3 times higher than in cotton and soluble polyhpenolics, a compound produced in all plants that can slow down decomposition, was about 3 times higher in corn than in cotton. These results indicate that the chemical characteristics of the plant parts added to soil, and where they are placed in the soil (on the soil or in the soil) makes a big difference in the rate of breakdown that occurs. This is important in hot climates becuase it is desirable to slow down breakdown. In addition, the results indicate that choosing the correct plant type, one with more polyphenol production, can improve the retention of soil carbon in hot climates. This information can be used to develop crop management practices that promote carbon retention.

Technical Abstract: Maintaining soil C is especially difficult in hot climates. Information is needed regarding the influence residue biochemical properties on residue decomposition in hot, semi-arid climates so that management practices that improve organic matter retention can be developed. Litterbags containing stalk or root tissues of senescent cotton (Gossypium hirsutum) or corn (Zea mays L.) were placed on the surface or 10 cm below the surface of a fallow Hidalgo sandy clay loam, and were monitored quarterly for one year for changes in mass loss, extractable C (WEC), water- and alcohol-extractable polyhphenolics (WEP and TPP, respectively). Surface-placed cotton residues retained more mass than when buried from ~80% (surface) to <50% (buried). For corn, retention ranged from ~60 to ~70% for surface residues to ~40% for buried residues. Most mass loss occurred within the first 3 months. The greatest increases in WEC (~1500 Ug Cg-1 for corn; ~500 ug Cg-1 for cotton) and WEP (~175-325 ug g-1) for corn also occurred within the first 3 months. WEP peaked (~100 ug g-1) in cotton residues at 6 months, while corn residues reached a maximum (~300 ug g-1 at 3 months. TTP decreased in cotton stem residues, from a ~5-8 ug g-1 to ~2 ug g-1. Surface cotton roots maintained ~6 ug g-1 after 3 months. Results emphasized the importance of residue moisture content during decompostion to several parameters, and indicate that different residues may have different capacities to hold moisture which may affect the biochemical characteristics and kinetics of decomposition.