Comprehensive definitions and indirect estimations: narrowing reasearch-reality gap in quantifying vegetable crop residues N

Summary

Vegetable crop residues (VCR) can pose environmental impacts in the form of leaching and nitrous oxide emissions, due to their high water contents, N concentrations but low C/N ratios, regardless of utilisation methods. It is vital to investigate its environmental impacts for future sustainable production systems. Carbon and nitrogen (N) concentrations and amount of biomass of VCR are essential parameters used for estimating environmental impacts of VCR utilisations. However, a dataset for those parameters is currently unavailable. In this review, we discuss challenges in accurately estimating VCR N and highlight factors to improve accuracy of estimation and to minimise misunderstandings. We compile the available data of these parameters for Different VCRs. N concentrations/contents, C/N ratios, other nutrient contents (P, K, S, and Mg) of VCR, and harvest index (HI) and nitrogen harvest index (NHI) of vegetables are overviewed for 72 crops across 27 countries with large variations in observation numbers based on published and unpublished data from open field and greenhouse productions. Indirect estimations on VCR are suggested as substitutes for direct measurements when techniques and resources are limited in practices and research. Nitrogen contents of VCRs can be calculated by using HI and NHI. Aboveground/belowground ratios of C and N concentrations as well as biomass of specific crops can be simulated by mechanistic models but require validations. Nitrogen contribution from VCR to cropping systems can be indirectly evaluated by soil mineral N concentrations. Above all, thorough investigations on VCR regarding aboveground/belowground ratios, nutrient concentrations (N, P, K, etc), C/N ratios and HI are needed for more accurate and comprehensive estimations on VCR. Additional research should be conducted to comprehensively investigate environmental impacts and consequences of different VCR utilisation options (handling, harvest, transportation, etc) and innovative utilisations of VCR to achieve more sustainable vegetable production systems.