Inorganic nitrogen dynamics under cover crops in Florida’s sandy soils

Abstract

Cover crops could help mitigate nutrient losses from soils in agricultural cropping systems, but little information exists about the fate of nitrogen (N) in sandy soils being cover cropped under a subtropical climate. The main objective of this study is to better understand soil inorganic N pools in cover cropped sandy soils and to examine how cover crops influence soil N cycling. A two-year experiment compared four cover crop treatments used in a vegetable system: sunn hemp (SH), a legume; sorghum sudangrass (SS), a non-legume; 50/50 mixture of sunn hemp and sorghum sudangrass (MX); and a weed fallow as a control (CT). Soil samples were collected at 0–15, 15–30 and 30–60 cm and analyzed for extractable NO3−–N and NH4+–N as well as for net N mineralization and nitrification rates following cover crop termination. Following cover crop termination, N mineralization and nitrification rates were higher under the cover crop plots compared to the control, indicating that the breakdown of cover crop residues increased soil inorganic N availability. While the SH treatment had the highest soil inorganic N after cover crop termination among the treatments, it also resulted in more inorganic N at 30–60 cm compared to 15–30 cm, indicating a possibility for greater N leaching under SH. This work highlights the need to consider soil N dynamics when cover crops are used in subtropical sandy soils and shows that there may be a tradeoff between inorganic N production for the subsequent cash crop versus potential N leaching in these systems.