Efficacy of Supplemental Irrigation and Nitrogen Management on Enhancing Nitrogen Availability and Urease Activity in Soils with Sorghum Production

The soil nitrogen (N) availability and urease activity (UA) in a humid ecosystem with variable rainfall distribution and poor soil fertility are not well understood. A complete appreciation of N cycling in the soil&ndash
water&ndash
plant continuum is needed to better manage N and water in regions that will be strongly affected by climate change. A sorghum (Sorghum bicolor L.) study located in Florence, South Carolina, USA, was conducted using a variable-rate pivot system. We hypothesized that supplemental irrigation (SI) and N would enhance UA and N uptake while minimizing the concentration of N in porewater (TINW). The aim of the study was to assess the impact of SI (0, 50, and 100%) and N fertilization (0, 85, and 170 kg N ha&minus
1) on: UA
total N (TNS)
total inorganic N (TINS)
TINW
and N uptake of sorghum. Results support our research hypothesis. The greatest UA was from 0% SI and 170 kg ha&minus
1 (18.7 &micro
g N g&minus
1 ha&minus
1). Porewater N (mg L&minus
1), when averaged across SI and N showed a significantly lower concentration at lower soil depth (9.9 &plusmn
0.7) than the upper depth (26.1 &plusmn
2.4). The 100% SI had the greatest biomass N uptake (NUPB) of 67.9 &plusmn
31.1 kg ha&minus
1 and grain N uptake (NUG) of 52.7 &plusmn
20.5 kg ha&minus
1. The greatest NUPB (70.9 &plusmn
30.3 kg ha&minus
1) and NUG (55.3 &plusmn
16.5 kg ha&minus
1) was from the application of 170 kg N ha&minus
1. Overall, results showed that proper use of water and N enhanced soil N dynamics, and improved biomass productivity and N uptake of sorghum.