Cover crop nitrogen reaches citrus fruit mainly after it decomposes
Yang X, Zeng L, Zhou Q, Xu L, Zhang J
Cover Crops
If you grow fruit trees with a living mulch like vetch underneath, timing matters: the real nitrogen payoff for your fruit comes after the cover crop dies back, not while it's still green and growing.
Researchers grew smooth vetch, a cover crop, under citrus trees and used a special nitrogen tracer to follow exactly where the vetch's nitrogen ended up. While both plants were actively growing, citrus trees barely touched the vetch's nitrogen, relying instead on nitrogen already in the soil. But once the vetch died and started breaking down, its nitrogen showed up in the citrus fruit, especially in trees that weren't given extra fertilizer, and a lot of it also got locked into the soil for long-term storage.
Key Findings
During co-growth, citrus nitrogen uptake came mainly from existing soil nitrogen, not directly from the living vetch (contribution index >1 under both fertilized and unfertilized conditions).
After vetch decomposition, fruit recovered more vetch-derived nitrogen than leaves (fertilized: 2.97% vs 1.09%; unfertilized: 4.20% vs 1.70%), with unfertilized fruit recovery about 1.5x higher than fertilized.
Fertilization increased vetch-derived nitrogen stored in particulate and mineral-associated organic matter (2.2x and 2.4x higher, respectively) but reduced it in microbial biomass by 33.6%, with soil retention in the top 10 cm (~9%) exceeding citrus uptake.
chevron_right Technical Summary
Scientists tracked nitrogen from cover crop vetch into citrus trees and soil using isotope labeling, finding that citrus mostly feeds on existing soil nitrogen while growing alongside vetch, but draws more heavily on vetch-derived nitrogen for fruit production once the vetch breaks down, especially when synthetic fertilizer isn't applied.
Abstract Preview
Original paper
Translocation and Allocation of Smooth Vetch-Derived Nitrogen Along the Plant-Soil Continuum in Citrus Orchards.
The dynamics and distribution of legume-derived nitrogen (N) throughout the phenological cycle in legume-based agroforestry systems remain poorly understood, limiting our understanding of N allocat...
open_in_new Read full abstractAbstract copyright held by the original publisher.
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