Does Meta-Analysis Adequately Assess the Interaction of the 4Rs of Crop Nutrition with Climate and Other Factors Impacting Nitrous Oxide Emissions?

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1 Does Meta-Analysis Adequately Assess the Interaction of the 4Rs of Crop Nutrition with Climate and Other Factors Impacting Nitrous Oxide Emissions? C.S. Snyder, PhD, CCA Nitrogen Program Director North America and Global Conway, Arkansas, USA T.W. Bruulsema, PhD, CCA Director, Northeastern Region North America Program Guelph, Ontario, Canada Joint Assembly of AGU-GAC-MAC-CGU Montreal, Quebec, Canada May 3-7, 2015

2 4R Nutrient Management Mismatched timing of N availability with crop need is probably the single greatest contributor to excess N loss in annual cropping systems. (Vitousek and Robertson Ann. Rev. Environ. Resour. 34:97-125) 4R Nutrient Stewardship initiative by industry with university, government, and conservation partners: based on principles of the right nutrient right rate, time, and place to achieve economic, social, and environmental sustainability (Bruulsema et al Crops Soils 42:13-18) site-specific, locally-sensitive 4R BMP optimization involves partners: including farmers, crop advisers, scientists, policymakers, consumers, and the general public Congruent with U.S. and International N Conference emphases on N use efficiency and just enough

3 In-Season Uptake and Recovery of Applied Fertilizer N by Cereal Grain Crops 45% to >85% Often < 40% research experiments on-farm Some suggest the pathway to reduced N 2 O is simply to reduce fertilizer N rates; or maximize N use efficiency Yet, highest crop N use efficiency (NUE; plant recovery of applied N) is usually achieved with lowest increment of N input It would be reprehensible and impractical to increase NUE by limiting N inputs to only the lowest rates Such action would greatly jeopardize sustainable food production J. Wang, LSU Fluid Journal

4 Musings on Meta-Analysis meta-analyses allow quantification of the impact of an experimental treatment relative to a control that is consistently defined across all studies evaluated (Source: Christianson and Harmel, 2015, unpublished; citing Arnqvist and Wooster, 1995; Hedges et al., 1999). Meta-analysis aggregates findings from similar studies; preferably those published in peer-reviewed scientific journals. But originality is an important criterion for publication. Thus, no two studies are fully similar. Does use of log transformation, log response ratios, inverse variance weighting lead to overemphasis of small emissions? Is the distribution of soils involved in existing studies representative of those used in agriculture? Is it correct to assume every farm can reduce emissions? 65% of emissions from 35% of the observations

5 Yield-Scaled Emissions vs. N Use Efficiency Cropping system NUE (i.e. apparent N recovery) improvements at modest fertilizer N rates correlated strongly with reduced yield-scaled N 2 O emissions (from meta analyses of 19 studies, 147 observations; van Groenigen et al., 2010) Each point: average of 3 studies, 27 observations each r 2 = 0.99 Source: A. Halvorson van Groenigen, J.W., G.L. Velthof, O. Oenema, K.J. Van Groenigen, and C. Van Kessel European Journal of Soil Science 61: van Groenigen et al Better Crops 95(2):16-17.

6 Recent Meta Analyses of N Management Changes on N 2 O Emission Reduction: Field Experiments Comparison technology or N practice Reference technology or fertilizer N practice Emission reduction (%) Urea with urease inhibitor (UI) Urea alone Nil Nitrification inhibitor (NI) or polymer coated urea (PCU) Fertilizer N with UI and NI Conventional N, no inhibitor or polymer coating Fertilizer N with no inhibitor 38 Comment [COSUST paper reference] 1 Akiyama et al., 2010; full dataset 35 published studies through 2008; 85 & 20 obs. for NI & PCU, respectively [36] 2 Decock, 2014; major corn regions of U.S. & Canada; 3 published studies through 2011, 20 observations [42] 3 1 Snyder, Davidson, Smith, and Venterea Curr. Opin. Environ. Sustainability. 9-10: range of agricultural crops 3 corn (maize)

7 Recent Meta Analyses of N Management Changes on N 2 O Emission Reduction: Field Experiments Comparison technology or N practice Reference technology or fertilizer N practice Emission reduction (%) Commercial fertilizer Manure 40 Comment [COSUST paper reference] Decock, 2014; major corn regions of U.S. & Canada; 9 published studies through 2011, 73 observations [42] 3 Fertilizer placement >5cm deep Fertilizer placement <5 cm deep >30 Van Kessel et al., 2013; >9 long-term field studies published before Aug. 2011, >50 comparisons; reduced tillage in humid & dry climates [26] 4 3 corn (maize) 4 range of agricultural crops, excluding rice

8 Example: Fertilizer N Source Effects on N 2 O Source: Eagle et al., 2015, unpublished; Nitrogen Losses: A Meta-analysis of 4R Nutrient Management in U.S. Corn-Based Systems (IPNI-2014-USA-4RM10)

9 Geographic Gaps: U.S. Corn N 2 O Studies Source: Eagle et al., 2015, unpublished; Nitrogen Losses: A Meta-analysis of 4R Nutrient Management in U.S. Corn-Based Systems (IPNI-2014-USA-4RM10)

10 Eastern Canada 4R Meta Analyses: an Update on Progress

11 Meta-analysis of FIE, g N 2 O-N/kg fertilizer N (n=120; from 10 published studies on corn in EC) mean 13.0 M 7.4 median 9.2 SE(M) 0.05 SE(mean) 1.32 M* 10.3 Q SE(M*) 0.91 C p* < T I 2 100% M = summary effect, fixed-effects model M* = summary effect, random-effects model (means weighted by inverse-variance) from Bruulsema, Bergeron, Rochette & Zebarth, 2011

12 Meta-analysis of right time on Corn 4 studies, 29 observations comparing application at planting (P) to application of most of the N as sidedress at V6 growth stage (S) Eastern Canada Drury, C. F., et al Soil Sci. Am. J. 76: Ma, B. L., et al Global Change Biology. 16: Roy, A. K., et al Can. J. Soil Sci. 94: Zebarth, B. J., et al Can. J. Soil Sci. 88: Roy and Bruulsema, 2013, unpublished report

13 Analysis of timing effect in Eastern Canada (n=29; 4 studies on corn) Time of application Emission, g N 2 O-N kg -1 N Planting (P) 16.1 V6 sidedress (S) 13.6 Mean S/P 0.85 Mean ratio (S/P) 1.45 Exp[mean log(s/p)] 1.08 Conclusion: no significant effect by any statistical method! Roy and Bruulsema, 2013, unpublished report

14 Published reports on N 2 O emission in Eastern Canada in studies reporting SRTP of N application Ontario Quebec New Brunswick Eastern Canada Cropland, Mha % poorly drained 28 Studies Observation s Obs/Mha % on poorly drained soil Woodley and Bruulsema, unpublished report, 2013

15 from Snyder et al., 2014, COSUST paper Broader management and policy focus should be on improved N use efficiency and effectiveness; for lower N 2 O emissions per unit of crop and animal product Improved intensification of management practices (not necessarily greater inputs) may result in more efficient water and fertilizer N use Sustainable use of other essential nutrients, water, and crop and livestock protection inputs is encouraged because they also affect N use efficiency and effectiveness

16 Summary Does Meta-analysis Adequately Assess 4R for N 2 O? Source - has large influence (>30% reduction) in some geographies Rate still important, but not the only R that should receive management and policy attention need N uptake measurement to evaluate excess or surplus Time - inconclusive owing to variable results Place - >5 cm in conservation tilled soils Data Gaps and Needs current dataset does not represent all combinations of soil and weather factors interacting with the 4Rs; need more locations future work should include crop N uptake, and other pathways of N loss need better methods to measure and predict soil conditions that present risks of N 2 O emission need more comparisons of other Rs across a range of applied N rates, to find optimal combinations and to evaluate interactions

17 Thank You Better Crops, Better Environment through Science