Abstract
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–water–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−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−1 (18.7 µg N g−1 ha−1). Porewater N (mg L−1), when averaged across SI and N showed a significantly lower concentration at lower soil depth (9.9 ± 0.7) than the upper depth (26.1 ± 2.4). The 100% SI had the greatest biomass N uptake (NUPB) of 67.9 ± 31.1 kg ha−1 and grain N uptake (NUG) of 52.7 ± 20.5 kg ha−1. The greatest NUPB (70.9 ± 30.3 kg ha−1) and NUG (55.3 ± 16.5 kg ha−1) was from the application of 170 kg N ha−1. Overall, results showed that proper use of water and N enhanced soil N dynamics, and improved biomass productivity and N uptake of sorghum.
Highlights
Sorghum (Sorghum bicolor, L.) production in the southeastern Coastal Plain region of the USA is becoming problematic because of the vastly variable climate along with the low water holding capacity and low fertility of the soils
The greatest urease activity (UA) was from 0% supplemental irrigation (SI) with 170 kg N ha−1 (18.7 μg N g−1 h−1), while the lowest UA was from the soils treated with 100% SI and 170 kg N ha−1 (8.5 μg N g−1 h−1)
Our results showed that soils applied with 170 kg N ha−1 had increased the total N uptake by about 73% when compared with the control
Summary
Sorghum (Sorghum bicolor, L.) production in the southeastern Coastal Plain region of the USA is becoming problematic because of the vastly variable climate along with the low water holding capacity and low fertility of the soils. The present and future climate alterations in this region could have the potential to significantly modify the cultural settings for sorghum production, with important implications of irrigation and nutrient management. The likely financial return from sorghum production may hinge on the water supply, soil productivity, and other inputs (i.e., fertilizers) that farmers are adding to the field. Sinclair and Ruffy [3] concluded that the major management drivers that improved crop yield are availability of water and soil N. Gonzales-Dugo et al [4] claimed that water supply and N availability can be modified by farmers to control plant growth. There has been a mounting awareness in reducing and enhancing irrigation technology due to current water scarcity in agricultural domains because of the current variable climate [1,5,6]
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