Organic Amendment History and Crop Rotation Effects on Soil Nitrogen Mineralization Potential and Soil Nitrogen Supply in a Potato Cropping System

Crop management practices influence readily and potentially available N in soil. In this study, we evaluated the effects of organic amendment history and crop rotation on potentially mineralizable N (N-0), mineralizable N pools, and field estimates of soil N supply in potato (Solanum tuberosum L.) production, and evaluated a suite of N availability measures to detect changes in these parameters. Preplant soil samples (top 15-cm) were collected from the potato year of a rotation trial in Maine during 2004 and 2005. Treatments included three crop rotations, with and without a history of organic amendment [solid beef (Bos taurus) manure] application: PB, potato-barley (Hordeum vulgare L.); PSPB, potato-soybean [Glycine max (L.) Merr.]-potato-barley; and PSBA/T, potato-soybean-barley-alfalfa (Medicago sativa L.)/timothy (Phleum pratense L.). The No and mineralizable N pools were determined by aerobic incubation at 25 degrees C and periodic leaching for 24 wk with a fixed-k approach. On average, historically amended soil had 35% higher values of N-0, and an 8% higher proportion of mineralizable N partitioned to the stable mineralizable N pool, compared with nonamended soil. Lower values of N-0, mineralizable N pools and some measures of N availability were measured in PSBA/T compared with PB and PSPB rotations. All tested measures of N availability detected management-induced changes in No and mineralizable N pools. The preplant nitrate, UV absorbance of 0.01 MNaHCO3 extract at 205 nm and particulate organic matter (POM)-N were the best predictors of field-based indices of soil N supply (r(2) = 0.50 to 0.73). Management-induced changes in the size and quality of mineralizable N should be considered in developing best N management programs through organic amendment application and crop rotations.