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Title: Evapotranspiration as a criterion to estimate nitrogen requirement of maize under salt stress

Author
item LACERDA, CLAUDIVAN - Universidade Federal Do Ceara (UFC)
item Ferreira, Jorge
item Liu, Xuan
item Suarez, Donald

Submitted to: Journal of Agronomy and Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2015
Publication Date: 7/23/2015
Citation: Lacerda, C.F., Ferreira, J.F., Liu, X., Suarez, D.L. 2015. Evapotranspiration as a criterion to estimate nitrogen requirement of maize under salt stress. Journal of Agronomy and Crop Science. 202(3):192-202. doi: 10.1111/jac.12145.

Interpretive Summary: Salinity is a worldwide problem that afflicts approximately 800 million hectares of irrigated land in semi-arid regions. Some investigators believe that extra nitrogen fertilization can circumvent the toxic effects caused by salinity; however additional fertilization under saline conditions can increase N losses to the environment and increase salinity problems. This work tested the hypothesis that by reducing the application of N, based on the decrease in plant water consumption (evapotranspiration) caused by increasing salinity, it is possible to reduce N loss without causing N deficiency or further yield loss in salt-stressed maize plants. We tested four levels of salinity (electrical conductivity) of irrigation water (S1 = 0.5; S2 = 2.5; S3 = 5.0; and S4 = 7.5 dS/m) and four N rates using outdoor soil columns. The N rates were as follows: N1: N recommendation for maize (2.6 g per column); N2: 0.3 times the N recommendation (0.78 g per column); N3: Reduction in N1 based on the decrease in evapotranspiration caused by salinity; N4: Reduction in N2 based on the decrease in evapotranspiration caused by salinity. The amounts of N for N3 and N4 were reduced (in relation to N1 and N2) by 7, 15, and 30% for 2.5, 5.0 and 7.5 dS/m, respectively. Salinity caused nitrate accumulation in the soil, but there was an inverse correlation between soil N-nitrate accumulation and plant growth. As a consequence of growth inhibition, less water and less nitrogen were extracted from the soil causing nitrate accumulation. Reduction in N application according to evapotranspiration (N3 rate) not only allowed plant growth and photosynthesis, but also increased N-use efficiency by plants and greatly reduced soil nitrate accumulation compared to N1 rate, at the same levels of salinity. In conclusion, reduction of N application, based on reductions in evapotranspiration, is a good strategy to reduce the risk of ground water contamination by nitrate leaching, and reduce fertilization cost, without causing additional damage to plant development under salt stress. This approach to N application is of interest to consultants and extension specialists and can be used by corn producers to achieve economic gain (less N applied) while reducing N loading to the ground water under saline conditions.

Technical Abstract: We tested the hypothesis that by reducing the application of N, based on the decrease in evapotranspiration (ET) expected due to increase in soil salinity, it is possible to reduce N loss without causing N deficiency or further yield loss in salt-stressed maize plants. We tested four levels of salinity of irrigation water (S1 = 0.5; S2 = 2.5; S3 = 5.0; and S4 = 7.5 dS/m) and four N rates using outdoor soil columns with five replicates. The N rates were as follows: N1: N recommendation for maize (2.6 g per column); N2: 0.3 times the N recommendation (0.78 g per column); N3: reduction in N1 based on the decrease in ET caused by salinity; and N4: reduction in N2 based on the decrease in ET caused by salinity. The amounts of N for N3 and N4 were reduced (in relation to N1 and N2) by 7 %, 15 % and 30 % for 2.5, 5.0 and 7.5 dS/m, respectively. Salinity caused NO3 accumulation in the soil, plant growth inhibition and stomatal closure. The low rates of N (N2 and N4) did not meet the N demand of maize plants, especially for low levels of salinity (control and 2.5 dS/m). On the other hand, based on the available growth data, physiological responses and nutritional status, one can conclude that plants under N1 and N3 had the same potential for final yield. For these N rates, reduction in N application according to ET (N3 rate) not only allowed plant growth and maize physiological responses, but also increased N-use efficiency and greatly reduced soil nitrate accumulation compared to N1 rate, at the same levels of salinity. We conclude that reduction in N application, based on reductions in ET, is a good strategy to reduce both the risk of ground water contamination by NO3- leaching and fertilization costs, without causing additional damage to plant development under salt stress.