LTRAS Executive Committee, 8 April 98

Committee members present: R. Ford Denison, Dennis Bryant, Graham Fogg,

Richard Plant, Robert Norris, Akbar Abshahi. (Louise Jackson could not

attend, but sent comments by email.)

Invited guests: Chris van Kessel, Willy Horwath

The committee reviewed proposals from Willy Horwath, Chris van Kessel, and

Ford Denison.

Horwath's proposal (submitted by his postdoc Olivier Devevre) requested

permission to collect 30 soil cores 25 mm in diameter to a depth of 30 cm

from each organic and conventional corn & tomato plot, in order to assess

changes in soil organic matter and nutrient sequestration. Given the small

core diameter and shallow depth of sampling, there was general support for

the proposal -- even for approval of similar proposals by Denison without

consulting the committee (the LTRAS Charter allows the Director to approve

proposals involving removal of < 1 kg soil/plot) -- until it became clear

that they intended to sample within the "Central Yield-Monitoring Area",

not just within the 17-m-wide (50-ft) "Experimental Areas" along the

eastern or western edges of the plots.

[Historical notes: The original LTRAS proposal, written by Cassman et al.

in 1990, called for an "unperturbed treatment area" 45 m wide. The

Executive Committee has adhered to this tradition, by prohibiting any

activities in the Yield Monitoring Area that could significantly affect

yields or future use of this area for low-impact measurements. (We

anticipate that technology for minimally-invasive measurements will

continue to improve.) The original proposal also called for a 20-m-wide

"monitoring area for lysimeters, observation wells, small component

studies, etc." The committee has allocated a larger Experimental Area (34

m total width) than originally proposed, but this area is not intended to

be a "sacrifice zone" where "anything goes." Nevertheless, the committee

has sometimes approved moderate-impact activities in the Experimental Area,

such as removal of large-diameter soil cores, provided that the area and

duration of impact from a given experiment is limited to a fraction of the

Experimental Area commensurate with LTRAS's 100-year planned duration.]

Members of the committee asked Willy whether he could limit his sampling to

the Experimental Area. After some discussion, it emerged that he planned

to compare isotope ratios in these samples with those in "time zero"

samples, which were collected throughout the plot. Willy and Chris

expressed various versions of the opinion that the committee was setting

such strict guidelines that no-one would want to do research at LTRAS. The

committee, which has approved 12 proposals so far (from 8 departments), was

not convinced by this argument. Ford pointed out that the restrictions

that one researcher finds burdensome allow us to provide other researchers

with the uniform plots and detailed plot history that may be essential to

their research. (This point was highlighted further in subsequent

discussions of Chris's 15N proposal; see below.) After some discussion,

however, the committee agreed that the sampling proposed would in fact have

minimal impact if it immediately preceded field tillage, and the sense of

the committee was that sampling in the Yield Monitoring Area should be

"avoided" rather than absolutely prohibited. The proposal was approved,

with one dissenting vote from Akbar Abshahi. Depending on the results from

these samples, Willy plans to return to the committee to request release of

archival soil samples for comparison.

The committee then discussed Chris's proposal to apply 1 g of N at 30% 15N

excess to a 1.5 x 1.5 m microplot in each of the wheat plots, to see

whether N-supplying power of the soil differs among these systems yet.

Louise Jackson asked, via email, how he planned to avoid lateral movement

of 15N. Other members of the committee also asked about this, both in

terms of the accuracy of his measurements (to continue over 2 growing

seasons) and contamination of the plot with 15N. Graham pointed out that

subsurface isotope ratios were quite uniform in 1993. Based on weed seed

movement, Robert Norris suggested that some 15N could move for meters

horizontally. Dennis pointed out that landplaning (for example) may move

soil large distances. Willy expressed concern that use of 15N would

preclude future use of the plots for natural-abundance work. Chris agreed

that this could be a problem, but suggested that enriched 15N-studies at

LTRAS will be essential, and are more common than natural-abundance

studies. Willy said that natural-abundance methods are relatively new, and

increasingly important; he then proposed that we reserve one phase of each

system for natural abundance studies, and prohibit use of enriched 15N in

those plots. There was some committee support for this idea, although

Richard questioned its statistical validity. At this point the committee

decided that such an important policy decision shouldn't be made without

wider discussion. It will be discussed at the next LTRAS General Committee

meeting. Chris wouldn't apply the 15N until winter, anyway, so we have

time to try to develop a policy that balances the conflicting interests of

enriched-15N users with natural-abundance researchers. The proposal was

not approved, but will be reconsidered after these policy issues are resolved.

Finally, the committee discussed Ford Denison's proposal to omit compost

from part of the Experimental Area of each organic tomato plot in 1999, to

see to what extent adequate fertility for good crop yields depends on

yearly application of compost at rates that exceed the statewide manure

supply of 1 ton/irrigated acre. The resulting data would also be used in

his comparison of established organic with transitional organic plots,

involving three "extra" plots not included in the main experiment. Louise

commented, by email, that "we must leave this row out of use for quite

awhile... even though changes in soil properties may be relatively small."

She suggested that it might be worthwhile if continued long enough to see

an effect. Ford suggested that the effects of omitting compost for 1 year

would only last 1-2 years, based on typical decay series for manure and the

fact that compost supplies only part of the available N (the rest comes

from SOM and WLCC). Committee members generally agreed, with respect to N,

but suggested that other effects might be longer lasting (of "unknown

duration", according to Robert). Dennis presented some data from a

preliminary trial in unassigned plot 3-6 showing that a single application

of compost (7 ton/acre) had doubled available P and Zn (later the same

season), compared to approximately a 50% increase in nitrate. Richard

suggested that Ford do some additional preliminary work to get a better

idea how long the effects of skipping a compost application might last.

Ford agreed to do this, by following up on last year's manure experiment in

plot 3-6 this summer, and return with a revised proposal if appropriate.

Several committee members also suggested that the size of the treated area

be substantially reduced. The proposal was not approved, but a revised

proposal could be reconsidered.