Present: Ford Denison, Will Horwath, Chris van Kessel, Akbar Abshahi, Don Phillips, Dennis Bryant, Robert Norris, Lee Jackson, Tom Kearney, Louise Jackson, Dennis Rolston, Graham Fogg, Gene Miyao, Bill Rains.

Horwath and van Kessel became members of the committee by unanimous consent.

Denison: should use of 15N-enriched tracers be restricted at LTRAS (e.g., prohibited in one phase of each cropping system), to prevent resulting errors in natural abundance (NA) methods?

Horwath: uses both NA and tracer methods. NA has more assumptions so can be harder to publish, but still very useful. So far, he’s using NA methods at LTRAS because we have complete set of archival samples, but also getting good results using 15N-enrichment at SAFS. Has had success keeping 15N-enriched microplots in rice contained reasonably well (<1 m movement in a year), but that would require that normal field operations go around the plot and then be simulated with hand operations in plot.

van Kessel: NA methods won’t be possible in plots that have received 15N-enriched materials.

Louise Jackson: even considering only tracer methods, unlimited use of 15N in a plot will lead to escalation as successive researchers need to add increasing amounts to see signal above increasing background.

van Kessel: location of microplot must be well-defined

Horwath: hasn’t seen significant 15N movement w/ furrow irrigation water in one year

Fogg: NA methods can be used to identify source of nitrate in groundwater (especially distinguishing animal waste from other sources), but not if 15N has been used (restriction to one phase doesn’t help for groundwater studies)

van Kessel: LTRAS plots are too small to allow separation of individual plot contributions to groundwater nitrate anyway. But NA studies near the surface won’t be significantly affected by 15N use in other plots.

Rolston: how is tillage done? one direction?

Bryant: bidirectional, to cancel soil movement. Also ripping & cross ripping and landplaning at an angle. Working around microplots would be very difficult and simulating some field operations by hand would be almost impossible.

Louise Jackson: what about drainage?

Bryant: surface drainage only, in winter. Ditch enlargement has reduced backup of water from one plot into another, but some backup can still occur. So N end of plots is most likely to be affected by 15N moving from another plot.

Phillips: One major goal of LTRAS is to encourage widespread faculty participation. Banning 15N use would limit faculty enthusiasm for participation.

van Kessel: 15N doesn’t change yield or physiology at rates typically used (no increase in total N applied) so wouldn’t affect other researchers except those using isotopes

Louise Jackson: most operations can be simulated by hand, other than ripping.

Horwath: maybe OK to rip through plots, but don’t landplane. For long-term (multiyear) studies, need at least 9 m² plots, which then need to be contained for years.

van Kessel: but much of 15N will be removed in harvested crops. After a while there’s not enough left to worry about.

Denison: we mostly seem to be talking about how to contain 15N in order to prevent the escalation effect Louise talked about, but are we in agreement that using 15-N enriched materials within a plot seriously threatens subsequent use of NA methods in that plot? If so, can we agree to ban 15N in one phase of each system, and then move on to discuss how 15N should be managed in the plots where it is allowed?

Rolston: supports this approach. Little risk of contaminating other phase.

After some additional discussion, we voted unanimously to ban 15N-enriched materials in one phase of each cropping system. We expect the current Executive Committee to follow this policy but it won’t become a "fundamental policy" (see LTRAS Charter) until confirmed at a second meeting.

We then continued discussion of management of 15N in plots where it is allowed. Much discussion between Louise Jackson and Chris van Kessel about use of contained plots (microcosms in cylinders) vs. uncontained plots. Cylinders have some scientific advantages and allow much of the 15N to be removed (as a large soil core) when done.

Rains and van Kessel: the hole may be more of a problem than the 15N.

More discussion of this point, followed by general agreement that 15 cm diameter cores to a 30 cm depth probably don’t cause much long-term damage, though locations should be carefully identified.

Denison: so far, the Executive Committee has restricted the more destructive research activities to "Exerimental Zones" within 50 ft of the E or W edge of each plot. The idea is to have long-term a yield records and archival samples representative of each cropping system without artifacts due to excessive sampling, ditches, etc., while still allowing research activities (in the experimental zones) that might (over the years) have an effect on yield or that have long-term consequences for noninvasive methods not yet invented. Comments?

Louise Jackson: OK for a while, but eventually the Experimental Area will be so impacted that we will need to use the central area.

Denison: but then the Core Area will soon have the same problem. [Afterthoughts: actually, I agree that at some point we should probably open the Core Area to more destructive research. Maybe in 2043, halfway through the experiment? The Experimental Area in each of our plots is bigger than an entire plot at SAFS.]

Bryant: so far, we’ve been able to accomodate all research requests in the Experimental Area and are in no immediate danger of running out of space.

Rolston: would isotopes be restricted to Experimental Area?

Denison: not necessarily, if there weren’t associated issues like trampling or removal of large cores.

Hsiao (by email): even in plots where 15N is used, maybe restrict to 40% of plot, allowing possibility of NA methods at other end of plot [at least until 15N moves that far?]

General discussion of the Experimental Area policy. No implacable opposition, but not clear that there is concensus to support this policy.

Reopened discussion of management of plots with 15N-enriched microplots.

Lee Jackson: is it feasible to "landplane around" a microplot?

Bryant: very difficult. Would have to set aside area at least 15 x 200 ft.

van Kessel: probably OK to landplane whole plot.

Abshahi: other operations also move significant amounts of soil.

Louise Jackson: compaction is a problem, so can’t skip ripping operation.

Bryant: problems of working around microplots are bad enough that should probably treat entire plot as a unit (i.e., manage normally).

van Kessel: agrees with Bryant. People proposing use of 15N should provide calculations estimating how much 15N will move how far.

Rains: should require monitoring of 15N in area near microplot.

Louise Jackson: the person using the microplot should do that anyway, to see how much of their tracer has been lost.

Denison: Currently the corn in this corn/tomato rotation relies on a winter legume cover crop (WLCC) for all of its N, but the tomato is grown with N fertilizer and no WLCC. Ken Cassman sent email explaining the original rationale for this system, but the original reasons (e.g., expectation that timing of tomato would be a major problem after a WLCC) haven’t proved out. If it’s OK to use fertilizer on the tomato, why not the corn?

Everyone agreed that cropping system 9 should probably be modified or replaced.

Denison: consider growing a WLCC both years to see how well a WLCC can supply N to summer crops, but maybe allow supplemental use of N fertilizer based on soil or plant tests.

Hsiao (email response to meeting agenda): water use by WLCC could raise sustainability concerns in California, but favors N application to corn year.

Liebhardt (by email): what is really needed at LTRAS is a treatment with longer rotations.

Denison: since we only have 6 plots in each system (currently 3 reps x 2 phases), eliminating system 9 wouldn’t let us have all phases of a 3-yr rotation. If we decided to have only one phase, we could actually have two different systems, but we wouldn’t have each crop growing each year in either system.

Kearney: tomato/wheat is most common rotation, but wheat/corn/tomato is also common.

Miyao: since we’re concerned about runoff, consider preventing runoff in winter in one system.

Bryant: flooding killed wheat in a wet winter even with our old, inadequate drainage system.

Norris: what about a no-N control with summer crops?

Denison: wheat no-N control should show how much production is possible without N inputs.

By show of hands, those remaining expressed support for development of detailed proposals for longer rotation and for revision of current system to include WLCC both years. Other options also worth considering.