Research paperIon exchange resin samplers to estimate nitrate leaching from a furrow irrigated wheat-maize cropping system under different tillage-straw systems

- No statistical differences in leaching between crops.
- Significant effect of tillage-straw management on leaching in maize.
- First field assessment of nitrate leaching in northern Mexico.
- Validation of the resin cartridge methodology in Vertisols.
- High residual soil N in both crops in the entire soil profile.

Nitrate (NO3-N) leaching from agricultural soils can lead to substantial losses of fertilizer nitrogen (N) and cause considerable contamination of aquatic ecosystems and groundwater. This study aimed at estimating NO3-N leaching losses for three tillage-straw management systems in the intensely cropped Yaqui Valley, Northern Mexico using ion exchange resin samplers. To this end data were collected in 2013/2014 from a tillage experiment established in 2005 as a randomized complete block design with two replications and three subplots on a Hyposodic Vertisol. Tillage-straw treatments were conventionally tilled beds with incorporated crop residue (CTB-straw incorporated), permanent beds with crop residue retained at the surface (PB-straw retained) and permanent beds with residue burning (PB-straw burned). Ion exchange resin samplers were installed at 90 cm depth in a consecutive crop rotation of wheat (Triticum durum L.) and maize (Zea mays L.) for 6 and 5 months, respectively (from first pre-plant fertilization to harvest). Leaching losses were higher with maize than with wheat cultivation (68.2 and 53.5 kg ha−1 season−1 NO3-N; P = 0.25). Tillage-straw treatment did not significantly affect NO3-N leaching in wheat, but it did in maize. NO3-N leaching for wheat was 51.1 kg ha−1 season−1 NO3-N in CTB-straw incorporated, 60.8 kg ha−1 season−1 NO3-N in PB-straw retained and only 46 kg ha−1 season−1 NO3-N in PB-straw burned. For maize, overall leaching losses were highest for PB-straw retained (81.9 kg ha−1 season−1 NO3-N), followed by 75.6 kg ha−1 season−1 NO3-N for CTB-straw incorporated and 47.7 kg ha−1 season−1 NO3-N for PB-straw burned. Soil NO3-N concentrations were significantly affected by sampling date and depth. PB-straw burned had highest residual soil NO3-N after crop harvest. Ion exchange resins-based NO3-fluxes displayed high spatial variability, therefore a large number of repetitions was necessary. As 19% of N applied to wheat and 34% of N applied to maize was lost through leaching, farming practices that could lower the risk of nitrate contamination during cropping should be promoted. Additional multi-annual studies are necessary to assess the effects of reduced irrigation, climatic variation and different fertilizer application on nutrient leaching in different tillage-straw systems of northwestern Mexico.