Date of Graduation

12-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Kristofor R. Brye

Committee Member

Edward E. Gbur

Second Committee Member

Nathan A. Slaton

Third Committee Member

Michelle A. Evans-White

Keywords

Pure sciences, Biological sciences, Carbon, Near-surface soil, Nitrogen, Rice, Rotation, Tillage

Abstract

Rice (Oryza sativa L.)-based cropping systems are different from other row crops due to the flood-irrigation scheme used from about one month after planting to a few weeks prior to harvest. The frequent cycling between anaerobic (i.e., flooding during the growing season) and aerobic (i.e., generally, the remainder of the year) conditions can influence the rate of soil organic matter (SOM) decomposition, which can greatly influence carbon (C) and nitrogen (N) storage and sequestration in the soil over time. Therefore, a study was conducted on a silt-loam soil (fine, smectitic, thermic, Typic Albaqualf) at the Rice Research and Extension Center near Stuttgart, which is in the Mississippi River Delta region of eastern Arkansas, to evaluate the long-term effects of rice-based crop rotations [with corn (Zea mays L.), soybean (Glycine max L.), and winter wheat (Triticum aestivum L.)], tillage [conventional-tillage and no-tillage (NT)], soil fertility (optimal and sub-optimal), and soil depth (0- to 10- and 10- to 20-cm) after 12 years (1999-2011) of consistent management on SOM, total and water-stable aggregate (WSA) C, total and WSA N, soil physical properties (WSA structure, bulk density, penetration resistance), soil chemical properties (Mehlich-3 extractable nutrients, pH, and electrical conductivity), and soil surface carbon dioxide (CO2) respiration. Results showed that SOM, total C, and total N concentrations increased over time under the NT treatment and in all rotations that did not include corn in the top 10 cm, but were not affected by the fertility treatment applied. The NT/0- to 5-cm treatment combination had 3 to 6 times greater WSA C and N content than all other tillage-depth combinations in the top 10 cm, which did not differ among one another. Despite rotation trends in total C and N, rotations with increased frequencies of corn generally had greater WSA C and N contents compared to rotations with wheat. However, there were no consistently significant differences in soil surface CO2 flux between tillage treatments and/or among crop rotations after 10- and 11-years of imposed treatment combinations. Results from this long-term experiment suggest that rice rotated with a higher-residue-producing crop, such as corn, may lead to greater C and N sequestration for longer periods of time due to the aggregated form that is predominantly present in the soil. It appears that the management practices of NT and high-residue-producing crop rotations establish a new, greater soil C content equilibrium over time. This long-term research study is important because the results enable a greater understanding of the decadal effects that rice-based crop rotations and conservation management practices have on the physical, chemical, and biological properties of the soil, which in turn, provides insight to the longer-term sustainability of these systems so that they can remain highly productive without detrimental effects to the environment and the soil resource.

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