SOIL AGGREGATION, AGGREGATE CARBON AND NITROGEN, AND MOISTURE RETENTION INDUCED BY CONSERVATION TILLAGE

Authors: Zibilske, Larry; Bradford, Joe

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2006
Publication Date: 4/5/2007
Citation: Zibilske, L.M., Bradford, J.M. 2007. Soil aggregation, aggregate carbon and nitrogen, and moisture retention induced by conservation tillage. Soil Science Society of American Journal. 71:793-802.

Interpretive Summary: Problems are caused by too little organic matter in agricultural soils. These are worse in the subtropics, where better management methods are needed, but have not been developed. Reducing soil tillage may help stop organic matter losses. We studied the effects of 13 years of not plowing the soil on the soil properties important in stopping erosion and improving soil fertility. These properties are aggregate formation, water holding capacity, and aggregate organic matter content. We grew cotton or corn on field plots, but it made little difference in this hot climate. We found that soil aggregates were more numerous on the surface when the soil was not plowed, but beneath the surface, not plowing made little difference in formation of soil aggregates. Water holding capacity was greater when the soil was not plowed and this let to higher amounts of organic matter build-up in the soil. Most of this fertility benefit, however, was restricted to the surface soil, presumably because the hot climate encourages organic matter breakdown at faster rates, compared to other climates, so build-up or organic matter is slower. Our results showed, however, that improvements to soil quality can still be achieved in a subtropical climate when better soil management practices are employed. More work needs to be done to determine how to increase the rate of improvement so farmers can see the economic benefits sooner.

Technical Abstract: Problems generated by deficient soil organic matter (SOM) levels are often acute in the tropics and subtropics, where better soil and residue management methods are needed, but have not been much studied. Conservation tillage may ameliorate SOM losses. We studied the effects of 13 y of plow tillage (CT), no-tillage (NT), and ridge-tillage (RT) on soil aggregation, moisture holding capacity, and aggregate C and N at two depths. Two cropping systems were tested, cotton (Gossypium hirsutum L.) alone and cotton followed by corn (Zea mays L.). The experiment was conducted on an Hidalgo sandy clay loam (fine-loamy, mixed, hyperthermic Typic Calciustoll). Few cropping systems differences were found. Aggregation was significantly higher at 0-5 cm depth with NT and RT in the >4750 and 500-212 'm size classes, but CT or RT dominated the other size classes. At 10-15cm, CT dominated all but the >4750 'm class. Water holding capacity from -10 to -100 kPa was significantly greater with NT and RT by more than 12% over CT management. Aggregate C and N content in NT and RT were higher than CT at 0-5 cm depth, but at 10-15 cm, CT and RT were higher. Mass weighted data revealed a more biphasic retention of C and N; more C and N in the >4750 'm and 500-212 'm classes. Results demonstrate the positive effects on C and N retention and water holding capacities achieved in a subtropical climate with the adoption of conservation tillage.