Seasonal Net Nitrogen Mineralization in the Topsoil of Subsurface Drip Irrigated Fields

Abstract

ABSTRACT Nitrogen (N) mineralized from soil organic matter during the growing season can be an important source of crop-available N. However, accurate estimates for subsurface drip irrigated fields are currently not available. The main objective of the study was to determine seasonal net N mineralization rates in subsurface drip irrigated fields in California’s Central Valley. Soil samples were collected regularly from the top 15 cm of eleven commercial fields during the growing season and subsamples were incubated at an optimal moisture content and at field moisture (soil moisture content at the time of sampling). Net N mineralization in field moist soil was on average 45% of the potential N mineralization. When corrected for daily soil temperature at the sites, net N mineralization during a 4-month period from April 15 to August 15 averaged 25.2 kg ha−1 (median = 20.7 kg ha−1), which corresponds to 10 to 20% of the N in the aboveground biomass of the crops grown in these fields. To achieve a high N use efficiency and limit the risk of nitrate leaching to the groundwater, net N mineralization from soil organic matter should be accounted for when planning N fertilizer applications.