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Accumulation and Crop Uptake of Soil Mineral Nitrogen as Influenced by Tillage, Cover Crops, and Nitrogen Fertilization

^a USDA-ARS-NPARL, 1500 North Central Ave., Sidney, MT 59270
^b Agricultural Research Station, Fort Valley State Univ., 1005 State University Dr., Fort Valley, GA 31030

View larger version (31K): [in this window] [in a new window]   Fig. 1. Distribution of (A) NH4–N and (B) NO3–N concentrations in the soil profile at the 0- to 120-cm depth averaged across tillage, cover crops, and N fertilization rates from May 2000 to November 2002 in Fort Valley, GA. LSD (0.05) is the least significant difference between sampling dates at a soil depth at P = 0.05.

View larger version (60K): [in this window] [in a new window]   Fig. 2. Effect of cover crops on soil NO3–N concentrations at the 0- to 120-cm depth averaged across tillage and N fertilization rates from May 2000 to November 2002 (A–F) in Fort Valley, GA. Rye denotes cereal rye; vetch, hairy vetch; vetch + rye, hairy vetch and rye biculture; weeds, winter weeds or no cover crop. LSD (0.05) is the least significant difference between cover crops at a soil depth at P = 0.05. No soil samples were collected from the 30- to 120-cm depth in May 2000.

View larger version (39K): [in this window] [in a new window]   Fig. 3. Effect of cover crops on soil NO3–N contents at the 0- to 120-cm depth in (A) 0 kg N ha–1, (B) 60 to 65 kg N ha–1, and (C) 120 to 130 kg N ha–1 averaged across tillage and soil sampling dates in Fort Valley, GA. R, denotes cereal rye; V, hairy vetch; V + R, hairy vetch and rye biculture; W, winter weeds or no cover crop. Bars followed by different lowercase letter within a soil depth are significantly different at P 0.05 by the least square means test. Bars followed by different uppercase letter at the top are significantly different at P 0.05 by the least square means test.

View larger version (43K): [in this window] [in a new window]   Fig. 4. Effect of (A) cover crops and (B) N fertilization rates on soil NO3–N contents at the 0- to 120-cm depth averaged across tillage and soil sampling dates in Fort Valley, GA. R, denotes cereal rye; V, hairy vetch; V + R, hairy vetch and rye biculture; W, winter weeds or no cover crop. Bars followed by different lowercase letter within a soil depth are significantly different at P 0.05 by the least square means test. Bars followed by different uppercase letter at the top are significantly different at P 0.05 by the least square means test.