Nitrogen Isotope Signatures in Grain Crops Treated with Organic and Chemical Fertilizers in a Four-Year Canola-Barley-Wheat-Canola Rotation.
Woo-Jung Choi, Dept of Biosystems and Agricultural Engineering, Institute of Agricultural Science and Technology, Chonnam National Univ, Yongbong-dong 300, Gwangju, South Korea, Muhammad Arshad, Dept of Renewable Resources, Univ of Alberta, Edmonton, AB T6G2E3, Canada, and Scott X. Chang, Univ of Alberta, 442 ESB, Edmonton, AB T6G 2E3, Canada.
Variations in crop grain and soil N isotope composition (d15N) as affected by liquid hog manure (d15N of total N was +5.1‰), solid cattle manure (+7.9‰) and chemical fertilizer (+0.7‰ for urea and -1.9‰ for ammonium phosphate) applications, and control (no fertilizer application) were examined through a 4-year crop rotation under field conditions. Canola (Brassica napus), hulless barley (Hordeum vulgare), wheat (Triticum aestivum), and canola were grown sequentially from 2000 (year 1) to 2003 (year 4). From year 2, hog manure or chemical fertilizers, but not cattle manure, treatments increased grain N concentrations over control. Grain d15N (+0.3 to +2.5‰) of crops applied with chemical fertilizers was lower than those in the other treatments, reflecting the effects of the 15N-depleted N source, while the manure treatments tended to increase grain d15N. The higher grain d15N of crops applied with hog manure (+5.6 to +8.4‰) than those applied with cattle manure (+2.2 to +4.1‰) reflected the higher N availability of liquid hog manure (up to 70% as ammonium) than solid cattle manure (99% organic N) and higher potentials for ammonia volatilization loss in hog manure rather than differences in manure d15Nsignatures. Soil total and extractable N concentrations and d15Ntended to vary with the application of N sources with different N isotope composition and availability. Our study expanded the application of the d15N technique for detecting N source (organic vs chemical) effects on N isotopic composition to field conditions and across a 4-year rotation, and revealed that N availability played a greater role than the d15N signature of N sources in determining crop d15N.