Abstract
Calibration of decision tools to improve N fertilizer management is critical to increase its adoption by maize (Zea mays L.) growers. The objective of this study was to establish nitrate and total nitrogen concentrations in the basal maize stalks (BMS) at harvest to separate maize fields among three N availability categories (N-deficient, N-optimum, and N-excess) under Mediterranean irrigated semiarid conditions. We analysed data from 26 irrigated maize trials conducted between 2001 and 2012. Trials included treatments receiving different N fertilizer rates and sources (mineral and organic), irrigation systems (flood, sprinkler) and soil types. The critical nitrate concentration in BMS to identify N-deficient plots (CNCL) is affected by the irrigation system. The CNCL was lower under sprinkler irrigation (708 mg NO3-–N/kg) than under flood irrigation (2205 mg NO3-–N/kg), and the later presented a higher degree of uncertainty compared to sprinkler irrigated systems. The results showed the difficulty to identify the N-deficient plots with the BMS test and the higher sensibility of nitrate-N than total-N concentration in BMS to separate N-deficient from N-optimal plots. Under sprinkler irrigation, nitrate in BMS>1500 mg NO3-–N/kg had a 85% probability of having received an excess of N. Considering economic net returns to N fertilization, the range of nitrate concentration in BMS that maximized profit under sprinkler-irrigated conditions was established between 1100 and 1700 mg NO3-–N/kg. Results suggest that BMS test can be useful in detecting plots with an excess of N but considering irrigation efficiency is crucial for stablishing successful CNC thresholds.
Highlights
The concentration in BMS to identify N-deficient plots (CNCL) was lower under sprinkler irrigation (708 mg NO3––N/kg) than under flood irrigation (2205 mg NO3––N/kg), and the later presented a higher degree of uncertainty compared to sprinkler irrigated systems
The results showed the difficulty to identify the N-deficient plots with the basal maize stalks (BMS) test and the higher sensibility of nitrate-N than total-N concentration in BMS to separate N-deficient from N-optimal plots
Maize (Zea mays L.) is one of the main crops grown in the irrigated areas of the Ebro river basin (Spain), with approximately 140,000 ha cropped each year (MAGRAMA, 2013)
Summary
Maize (Zea mays L.) is one of the main crops grown in the irrigated areas of the Ebro river basin (Spain), with approximately 140,000 ha cropped each year (MAGRAMA, 2013). High nitrate concentrations have been measured in drainage return flows from maize fields and this crop has been recently recognized as one of the main contributors to nitrate pollution of surface and ground waters (Cavero et al, 2003; Causapé et al, 2004a; Isidoro et al, 2006) in the Ebro river basin. Several irrigated areas in the basin have been declared vulnerable to nitrate leaching by Regional governments following the EU Directive (EC, 1991). In those areas, action programs impose limitations to the amounts of N fertilizer that can be applied to crops, which should be consistent with good agricultural practices and consider the specific characteristics of each farm such as realistic yield goals and N inputs from the soil and from irrigation water. It is necessary to develop decision tools for N management based on soil or plant N critical levels that can be implemented by growers in order to minimize N losses from maize fields while maintaining high yields
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