Graduate Thesis Or Dissertation
 

Fallow water retention and wheat growth as affected by tillage method and surface soil compaction

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gb19f8062

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  • No-tillage winter wheat (Triticum aestivum L.) grown in a wheat-fallow cropping system has consistently produced lower grain yields than conventionally tilled soils in the semiarid Pacific Northwest. A 2-year study was conducted in a long-term tillage trial at Moro, OR to determine factors responsible for differences in wheat growth and yield as affected by moldboard plow, stubble mulch, and no-tillage fallow method. Soil water, soil mineral N, plant N uptake, soil temperature, above-ground dry matter accumulation, and yield components were measured. The highest fallow efficiency during both years was achieved by stubble mulch tillage, followed by the plow and no-tillage systems. Accelerated water loss from no-tillage fallow occurred during the hot, dry summer due to uninterrupted capillary flow. The main yield limitations to no-tillage technology in this study were: (1) diminished seedzone water at planting time in the fall which resulted in reduced germination and stand establishment; (2) cooler spring soil temperatures which slowed crop development and dry matter accumulation, and; (3) production of fewer spikes per unit area. The second objective of this study was to determine if late season seedzone water loss from fallow could be reduced by altering the physical characteristics of the dust mulch. Loss of seedzone water appears to accelerate in late August and September because of increased diurnal heat flux. Compacting the soil surface with a roller in mid-August increased surface bulk density and volumetric water content to depths as great as 10 cm. Evaporative water loss from compacted plots, however, occurred at a faster rate than from control plots and, by mid-September, there were no differences in seedzone water content among treatments. Increased soil thermal conductivity appeared to be the reason for accelerated water loss in compacted treatments. Although water loss occurred at a faster rate in compacted treatments, compacting fallow soils with a roller immediately prior to fall seeding may increase winter wheat germination, emergence, and stand establishment during years of marginal seedzone water.
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