Thesis
Tree and soil nitrogen responses to alternative ground cover management strategies in organic apple production
Washington State University
Master of Science (MS), Washington State University
2009
Handle:
https://hdl.handle.net/2376/101255
Abstract
Organic mulches and cover crops are options for weed control, nutrient supply and soil quality management in organic orchards. This study examines the effects of ground cover management and compost rate on 1) tree performance, 2) internal cycling and partitioning of apple tree N, 3) N-use efficiency, 4) soil N supply and 5) soil biological activity. Wood chip mulch, cultivation, brassica seed meal and bare ground treatments resulted in higher fruit yields and tree growth, regardless of compost rate, than legume and non-legume cover crop treatments. Trees with wood chip mulch had greater dry weight and N accumulation in vegetative tree components than cultivated or legume cover cropped trees. Fruit yield in the cultivated treatment was similar to the wood chip treatment, despite reduced vegetative growth, as the cultivated treatment partitioned more dry weight into fruit (44%) than the wood chip treatment (31%). In the legume cover crop treatment, 20-100% of cover crop biomass N was derived from compost in the legume cover treatment, reducing compost N-use efficiency by trees compared to wood chip and cultivation treatments. Tree reserves were an important source of N for fruit and leaf growth in all treatments, but more so for trees under cultivation. Trees allocated 72% of spring N uptake into leaves and fruit and 71% of summer N uptake into woody tissues, bolstering N reserves. Compost rate influenced total soil N, while ground cover management affected the soil microbial community, but not total soil N. From September 2005 to September 2007, the high compost rate increased total soil N in the non-legume cover crop, wood chip mulch and cultivation treatments. Wood chips and brassica seed meal increased earthworm densities compared to other ground covers. Root colonization by mycorrhzal fungi was greatest in non-legume cover and unfertilized control treatments and cover-cropping increased soil microbial activity. In this experiment, improvements in soil N supply and microbial activity did not always translate into better tree performance. Wood chip mulch offered the best balance between improving soil quality and enhancing tree performance in a young organic apple orchard.
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Details
- Title
- Tree and soil nitrogen responses to alternative ground cover management strategies in organic apple production
- Creators
- Daniel Gerald TerAvest
- Contributors
- John P. Reganold (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Crop and Soil Sciences, Department of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525014401842
- Language
- English
- Resource Type
- Thesis