Soil microbial dynamics as affected by tillage, crop sequence, and N fertilizer /
Crop management strategies that alter the timing, placement, quantity, and quality of crop root and residue inputs can affect the size, turnover, and vertical distribution of active and passive pools of soil organic matter (SOM). The active pools of SOM, including mineralizable C and N and soil mic...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1995.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=742161571&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Crop management strategies that alter the timing, placement, quantity, and quality of crop root and residue inputs can affect the size, turnover, and vertical distribution of active and passive pools of soil organic matter (SOM). The active pools of SOM, including mineralizable C and N and soil microbial biomass (SMB), determine soil nutrient availability through mineralization and C sequestration from plant residues into SOM through immobilization. The objectives were to determine nal and long-term changes in in situ soil C02 evolution, inorganic N accumulation, C and N mineralization, and SMB in sorghum [Sorghum bicolor (L.) Moench.], wheat (Triticwn aestivwn L.), soybean [Glycine max (L.) Merr.], sorghum-wheat/soybean, and wheat/soybean sequences under conventional tillage (CT) and no tillage (NT) with and without N fertilizer. A Weswood silty clay loam (fine, mixed, themiic Fluventic Ustochrept) in south-central Texas was sampled (i) at three increments to 200 nun depth at planting, flowering, and harvest of sorghum and wheat and (ii) to one depth 57 times during a 2-yr period. Soil organic C, SMB, and mineralizable C at 0 to 50 mm depth were 33 to 125% greater under NT than under CT. Increasing cropping intensity from monoculture production of sorghum and wheat to rotation sequences increased SMB and mineralizable C 20 to 30%. Soil from NT generally remained wetter, denser, and warmer and released more CO, than soil from CT during 6 to 7.5 month fallow periods. Active and passive pools of SOM underwent (i) changes in vertical distribution as a result of surface placement of crop residues with NT, (ii) seasonal changes due to rhizodeposition and crop residue inputs, which increased potential C mineralization, but temporarily reduced potential N mineralization, and (iii) long-term changes due to the quantity and N concentration of crop residues produced. Conversion from CT to NT may have increased C sequestration and decreased loss as C02 during the initial years, but soil under NT released similar or greater quantities Of C02 upon attainiment of higher SOM content after nine years. High clay content soils of central Texas can be effectively managed to increase active and passive pools of SOM using minimal fallow and NT. |
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| Item Description: | Vita. "Major Subject: Soil Science". |
| Physical Description: | xiii, 161 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |