Efficacy of supplemental irrigation and nitrogen management on enhancing nitrogen availability and urease activity in soils with sorghum production

Authors: Sigua, Gilbert; Stone, Kenneth; Bauer, Philip; Szogi, Ariel

Submitted to: Sustainability
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2020
Publication Date: 10/12/2020
Citation: Sigua, G.C., Stone, K.C., Bauer, P.J., Szogi, A.A. 2020. Efficacy of supplemental irrigation and nitrogen management on enhancing nitrogen availability and urease activity in soils with sorghum production. Sustainability. https://doi.org/10.3390/su12208358.
DOI: https://doi.org/10.3390/su12208358

Interpretive Summary: In more humid regions like the southeastern Coastal Plain region of the U.S. with much hotter and drier conditions as results of the recent changing climate that brought water-scarce conditions will likely affect both crop and soil productivity. As the availability of irrigation water decreases and potential costs and increase regulation of nitrogen (N) use, there is a need to better understand how irrigation levels interact with N fertilizer rates. Our hypothesis in conducting this study was that supplemental irrigation in combination with N application would enhance N availability, N uptake, and urease activity while minimizing concentration of N in soil porewater. The objective of our field study was to determine the combined effects of N fertilization (0, 85, and 170 kg N/ha) and supplemental irrigation (SI: 0, 50 and 100% of the full irrigation rate) on total N (TNS) and total inorganic N (TINS) in soils, porewater N, biomass N uptake (NUB) at different growth stages (GS), and grain N uptake (NUG) of grain sorghum. We demonstrated that our results support our hypothesis that the negative impacts of water stress and nutrient deficiency could be mitigated by supplemental irrigation and N fertilization in sorghum production. Our irrigation (SI) and N treatments have highlighted the importance of water and N availability in sorghum production and soil sustainability in humid Coastal Plain region. While it appears that application of 170 kg N/ha with 100% supplemental irrigation resulted in the greatest NUB (69 kg N/ha) and NUG (56 kg N/ha), these treatments also resulted in significantly lower concentration of porewater nitrate (NO3) from soil depth between 30-100 centimeter (cm) when compared with the EPA’s threshold concentration of NO3 for drinking water. Sorghum in our study take up the majority of N (87.4 kg/ha) at 60 DAP. Nutrient uptake increases rapidly from 30 DAP to 60 DAP and then stay at high levels until 90 DAP when N uptake slows down (45.9 kg/ha). These N dynamics are important for agronomic reasons. Our results suggest that effective use of water in irrigation and maintaining a sufficient amount of N will improve the N uptake of grain sorghum and could enhance urease activity in soils while minimizing the concentration of porewater NO3 in humid Coastal Plain region of the U.S.

Technical Abstract: The dynamics and utilization of soil nitrogen (N) and urease activity (UA) in humid terrestrial ecosystem with poor rainfall distribution and poor soil fertility are not well understood. A holistic understanding of N dynamics in the soil-water-plant continuum is needed to better manage N and water inputs in regions with supplemental irrigation practices. A sorghum (Sorghum bicolor L.) study was conducted in the southeastern Coastal Plains under a variable-rate center pivot irrigation system. This study was carried out under the hypothesis that supplemental irrigation in combination with N application would enhance N availability, N uptake, and UA while minimizing concentration of N in soil porewater (PWN). The objective of our field study was to determine the combined effects of N fertilization (0, 85, and 170 kilogram N per hectare; kg N/ha) and supplemental irrigation (SI: 0, 50, and 100 percent, % of the full irrigation rate) on the following five variables measured at different growth stages (GS) and grain N uptake (NUG) of sorghum: 1) total soil N (TNS); 2) total soil inorganic N (TINS); 3) UA, 4) PWN; and 5) biomass N uptake (NUB). Total N in soil and TINS, as well as UA in soil varied significantly with SI (p=0.0001), levels of N (p=0.0001), and GS (p=0.0001). The greatest UA in soil of 11.86 ±5.27 and 11.72±6.15 microgram N per gram per hour (µg N/g/hr) were observed from 0% SI and N application of 0 kg N/ha, respectively. Porewater N varied significantly with the interaction of N x SI (p=0.01). Porewater N when averaged across SI and N showed a significantly lower concentration of 8.54±0.69 milligram per liter (mg/L) at lysimeter depth (LD) of 30-100 centimeter (cm) when compared with 26.03±2.38 mg/L at LD of 0-30 cm. The greatest NU in biomass (65.2±31.1 kilogram per hectare; kg/ha) and grain (52.5±20.5 kg/ha) of sorghum were obtained from SI of 100%. Application of 170 kg N/ha resulted in the greatest NUB (69.1±31.1 kg/ha) and NUG (56.1±16.5 kg/ha). Moisture shortage with equal availability of N reduced uptake of N. Overall, results support our hypothesis that SI in combination with N application would enhance N availability, NU, and UA while minimizing the concentration of PWN. Effective use of water in irrigation and maintaining a sufficient amount of N will improve sorghum productivity and efficient use of N fertilizer in Coastal Plains region of U.S.