soil total N pool by 209% at spring wheat harvest, and it did not affect spring wheat ...... spectrometry at the Stable Isotope Facilities, University of Saskatchewan,.
Nutrient Cycling in Agroecosystems Amending soil with used cooking oil to reduce nitrogen losses after cole crop harvest: A 15N study --Manuscript Draft-Manuscript Number:
FRES-D-14-00181R1
Full Title:
Amending soil with used cooking oil to reduce nitrogen losses after cole crop harvest: A 15N study
Article Type:
Full papers
Keywords:
15N tracer; carbon amendment; nitrate-nitrogen; broccoli; vegetable
Corresponding Author:
Laura L. Van Eerd University of Guelph Ridgetown Campus Ridgetown, ON CANADA
Corresponding Author Secondary Information: Corresponding Author's Institution:
University of Guelph Ridgetown Campus
Corresponding Author's Secondary Institution: First Author:
Katelyn A Congreves
First Author Secondary Information: Order of Authors:
Katelyn A Congreves R. Paul Voroney Laura L. Van Eerd
Order of Authors Secondary Information: Abstract:
After cole crop harvest, over 400 kg N ha-1 may remain in the field as crop residues and soil mineral N. Thus, methods to reduce potential post-harvest N losses are needed. Urea with 5% 15N excess was incorporated in mini-plots to produce 15N enriched broccoli (Brassica olecerea var italica L.). The fate of above-ground crop residue-derived N (15Nresidue-above) and below-ground residual fertilizer or root biomass N (15Nresidue-below) were studied from broccoli harvest (Aug and Sept 2011) to spring wheat (Triticum durum L.) harvest (July 2012), with and without an amendment of used cooking oil. The 15Nresidue-below remained mostly as organic N, was not influenced by the amendment, and was resistant to post-harvest losses. With the oil amendment, soil mineral 15Nresidue-above was reduced by 19 kg ha-1 and microbial biomass 15Nresidue-above was increased by 21 kg ha-1 two weeks after broccoli harvest, indicating immobilization of 15Nresidue-above and reduced potential N losses. At spring wheat harvest, amended soil had greater total, organic, and mineral soil 15Nresidue-above compared to the unamended control, by 44, 43, and 0.75 kg ha1, respectively. The amendment increased the recovery of 15Nresidue-above in the soil total N pool by 209% at spring wheat harvest, and it did not affect spring wheat yields or plant 15Nresidue-above content. It is possible that the amendment facilitated the incorporation of 15Nresidue-above into organic compounds, which were less susceptible to losses. Growers should consider applying used cooking oil at harvest to minimize potential N losses and to increase the soil organic N fraction.
Response to Reviewers:
All reviewer comments and edits were incorporated into the manuscript or justification provided below. Reviewer #1: R1: The comments are in the attached file. LVE: File was reviewed and edits incorporated or provided below. R1: The "exponential model" should be removed. (from the attached manuscript file: “This is not an exponential model - not in reality. There are two groups mapped shortly
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after harvest and later; this figure and this kind of modeling is not necessary. this figure and this kind of modeling is not necessary” LVE: The phrase ‘exponential’ was replaced with relationship. The figure has been modified to improve resolution. The figure itself and the empirical relationship were not removed. Unfortunately, without further explanation, it is difficult to assess why the reviewer suggests this revision. Other researchers have used this type of modelling, which is necessary for predicting N dynamics. In fact, De Neve and Hofman (1996) and (1998) used similar empirical relationships to predict N dynamics in cole crop systems. The figure demonstrates temporal changes that the tables do not demonstrate. The figure and empirical relationship help convey the temporal dynamics of N and the fate of N over time. The other two reviewers found no fault with the figure or empirical relationship, and thus the decision was made to keep the figure in the manuscript. In order to accommodate the reviewers’ view, at first mention of Fig. 1 the following text was inserted: “The first order exponential model (Fig. 1) demonstrates temporal changes in N fate and is necessary for predicting N dynamics. For instance, De Neve and Hofman (1996; 1998) used similar empirical relationships to predict N dynamics in cole crop systems.” R1: (from the attached manuscript file: “Do not use A from the equation but rather the experimental results”). LVE: Inserted into the sentence ‘based on the model (Fig. 1)’ R1: from the attached manuscript file: “please remove this part [in Fig. 1]” LVE: model equation not removed, for reasons outlined above. R1: The results should analyzed separately for 0-30 cm and 0-60 cm, since the depth can not be a factor, the data are not independent. LVE: It is true that 0-30cm and 0-60cm depths are not independent. However, analysis evaluated 0-30 and 30-60cm sample depths. Perhaps this was not clear and led to confusion. A brief description is now included in Material and Methods section to reduce any ambiguity associated with the statistical analysis. It now reads “If there was a depth x treatment interaction, indicating that the treatment had a different effect depending on the depth increment, the 0-30 and 30-60 cm soil depths were separated to investigate the treatment effect. However, if there was no significant depth x treatment interaction, indicating that the treatment had a similar effect within both depth increments, the 0-30 and 30-60 cm data were summed and the 0-60 cm profile was used to investigate the treatment effect.” LVE: It is very appropriate to use an ANOVA with soil depth as a fixed effect; numerous studies have done so. If we re-analyzed the data according to this reviewer’s suggestion, it would be statistically inappropriate (because one should not investigate the 0-60 cm depth if there was a significant depth increment x treatment interaction). A treatment x depth interaction (P
