Competition for 15N-labeled nitrogen in a jujube tree (Zizyphus jujuba Mill.)/wheat (Triticum aestivum L.) agroforestry system in northwestern China

Abstract

The degree of tree-crop competition for nitrogen (N) and its effect on fertilizer-use efficiency and N movement were examined in a jujube tree (Zizyphus jujuba Mill.)/wheat (Triticum aestivum Linn.) agroforestry system during 2011–2012. Assessment of competition was accomplished via the installation of an experiment with five imbedding depths (20, 40, 80, 120 and 200 cm) of 15N-enriched CO(NH2)2 and two configuration patterns (sole and intercropped treatment). The percentage of N derived from fertilizer (NDFF) and fertilizer-use efficiency (UFN) were determined using 15N-enriched CO(NH2)2 (5.22% atom enrichment) applied at 8 g N per plant. Land equivalent ratios of the jujube/wheat intercropping system reached maximum ratios of 1.45 for grain (fruit) yield and 1.67 for biomass in 2011 and 1.38 for grain (fruit) yield and 1.59 for biomass in 2012. The alley cropping yield decreased significantly compared to sole-cropped plants in both years, as did the biomass of intercropped wheat in 2012. This study showed a significant difference in nitrogen acquisition between intercropping and the expected value for the various depths in both years. The %NDFF of the two plants showed significant differences between intercropping and the expected value at various depths in both years, and the intercropped %NDFF was higher than the expected value. The total UFN data, which represented an increase in response to intercropping, indicate that plants in the intercropping treatment had a higher UFN than the expected value. The UFN for jujube trees in all treatments was lower than that for wheat, indicating less uptake and utilization of N fertilizer. Management interventions, particularly those that increase fertilizer in the shallow layer may be critical for the success of this system.