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Assessment of the Amino Sugar–Nitrogen Test on Iowa Soils

I. Evaluation of Soil Sampling and Corn Management Practices

Department of Agronomy, Iowa State Univ., Ames, IA 50011-1010

View larger version (22K): [in a new window]   Fig. 1. Comparison of amino sugar–N test (ASNT) values from soil collected at the 0- to 30-cm depth in fall, early spring, and late spring at 43 N rate trials. ***Statistically significant at the 0.001 probability level.

View larger version (29K): [in a new window]   Fig. 2. Amino sugar–N test (ASNT) values from four N rate trials sampled throughout the year in 2002 and 2003 at two soil depths. Vertical dashed lines show the change in ASNT values between 14 d sampling periods in fall, early spring, and late spring sampling periods.

View larger version (32K): [in a new window]   Fig. 3. Comparison of amino sugar–N test (ASNT) values at two sample depths and the ratio of ASNT values (0- to 15-cm divided by 0- to 30-cm) at 43 N rate trials. Test values are from fall, early spring, and late spring sampling periods.

View larger version (30K): [in a new window]   Fig. 4. Amino sugar–N test (ASNT) values as a result of long-term crop rotation history. Soil samples were collected in the fall of 2002 after harvest and when corn was to be planted in the rotation in 2003. The bold, underlined crop letter indicates the crop in the rotation when the soil samples were collected. CCCC, continuous corn; CCOA, corn–corn–oat–alfalfa; CCS, corn–corn–soybean; COA, corn with alfalfa in the rotation; COAA, corn–oat–alfalfa–alfalfa; CS, corn with soybean in the rotation; CSCS, corn–soybean–corn–soybean.

View larger version (15K): [in a new window]   Fig. 5. Amino sugar–N test (ASNT) values as a result of long-term N fertilizer application history. Soil samples were collected in the fall of 2002 after harvest and when corn was to be planted in the rotation in 2003. *Statistically significant at the 0.05 level. ***Statistically significant at the 0.001 probability level.