Changes in Soil Carbon and Nitrogen Due to Irrigation Development in Nebraska's Sandhill Soils

Abstract

Abstract Carbon and N parameters were compared for nondeveloped and developed soils (predominantly mixed mesic, Typic Ustipsamments, and sandy, mixed mesic Entic Haplustolls). Soil samples were collected from four developed center pivot irrigation sites and from the nondeveloped corners at depth increments of 0‐ to 75‐, 75‐ to 150‐, and 150‐ to 300‐mm. Total C, total Kjeldahl N (TKN), hydrolyzable N, and mineralizable N by autoclave and by a 112‐d incubation study were determined. Changes in TKN were not significant in the 0‐ to 75‐mm depth, but in the second depth increment, TKN increased with development (507 to 569 kg ha −1 ). Total C also increased at this depth (5650 to 6400 kg ha −1 ). The C/N ratio increased with development in the surface 75 mm (11.5 to 12.2). Inorganic N increased in the top 300 mm due to development. Mineralizable N by both techniques increased in the 75‐ to 150‐ and 150‐ to 300‐mm depth increments. Steady state values for ln TKN were calculated to be 6.6, 6.4, and 6.8 kg ha −1 for soil depth increments of 0‐ to 75‐, 75‐ to 150‐, and 150‐ to 300‐mm, respectively. The ln total C steady‐state values were 9.1, 8.8, and 9.1 kg ha −1 . In some cases, undeveloped soil contained more N and C than these steady‐state values, suggesting that development tended to decrease the soil test values. If the undeveloped soil was lower in N or C than the steady‐state value, development tended to increase the test value. Total C, TKN, hydrolyzable N, mineralizable N (both techniques), and inorganic soil N were all highly correlated. Changes in TKN and total C were not correlated to landscape position or time since development.