Investigating the Legume Green Fallow Alternative on North-Central Montana No-Till Operations

2010 Annual Report for GW10-032

Project Type: Graduate Student
Funds awarded in 2010: $24,250.00
Projected End Date: 12/31/2010
Grant Recipient: Montana State University
Region: Western
State: Montana
Graduate Student:
Major Professor:
Dr. Perry Miller
Montana State University

Investigating the Legume Green Fallow Alternative on North-Central Montana No-Till Operations


We have been conducting an on-farm study working with six no-till wheat producers in north-central Montana using a legume green fallow (legume green manures and/or forage crops) as a summer fallow alternative. These producers hope to maintain or improve wheat yields and reduce their N fertilizer costs by including a legume in their wheat rotations. Historically though, legume green fallow (LGF) crops in this dryland cropping region have been known to reduce wheat yields through excessive soil water use. This study has an original focus on LGF treatments exclusively using no-till management and early legume termination for increased water conservation. Plot-scale studies indicate that these practices increase LGF viability, and we have likewise been evaluating soil water use, soil N levels, wheat yields and producer feedback to examine LGF viability in a farmer-managed, field-scale setting.

To date, we have assessed soil water and N dynamics and are currently assessing wheat yields and producer initiative to continue using LGF crops. Preliminary results are indicating that wheat yields following LGF will likely be equal to or slightly lower than following summer fallow, which may be due to a lack of N mineralized from crop residues rather than by a lack of soil water. Producer feedback also indicates that factors such as LGF crop seed costs and a lack of dramatic immediate LGF benefits to wheat yields may also be substantial barriers to adoption of LGF practices. In November 2010, the preliminary results of this project were presented in a poster session at the ASA/CSSA/SSSA international meeting in Long Beach, CA, and in August 2010 it was included on a field day tour in north-central Montana. To date, this project is showing considerable promise to elucidate no-till LGF viability and future adoption potential in this principal wheat-growing region of Montana.

Objectives/Performance Targets

1) Quantify the effects of LGF on soil N contributions, soil water use and the effect they have on the following wheat crop compared to summer fallow.

2) Assess how no-till management and early termination may affect LGF management.

3) Assess LGF management over regionally varied sites and management practices by different producers.

4) Conduct a marginal economic analysis of LGF management compared to standard summer fallow under no-till management.

5) Assess producer initiative to continue LGF management based on results of the study.


Progress since 2009

We have recently completed the second and final field season of this project. All six producers involved in this project successfully planted and harvested a wheat crop across all green fallow and summer fallow treatments at each site in 2010. All data collection procedures for this project are nearing completion, and analyses have begun. Preparations are also currently being made to conduct a videotaped interview the producers involved; so far five of six producers have agreed to be videotaped.

Preliminary Summary of Results

- At one site, soil water values under LGF equaled summer fallow values by wheat seeding in September, apparently from a single rainfall event. Other sites also measured at seeding showed small total water deficits after LGF crops (deficit across all sites: range = 15 - 31%, median = 19%, 0-90 cm soil depth). This indicated potential for soil water values under LGF to reach values close to summer fallow by spring with the addition of over-winter and early spring rainfall. Past studies have also shown that small water deficits are unlikely to limit yields. Additionally, there was high growing season rainfall at all sites (est. 150-200 mm) and generally high wheat yields at most sites, suggesting water was not likely a primary limiting factor of yield potential during this crop year.

- Values reflecting soil N before seeding (preliminary nitrate deficit across four sites: range = 36 - 56%, median = 42%, 0-90 cm soil depth) suggest biomass N may not be substantial enough to have mineralized sufficient N for wheat uptake of N to equal fallow values and produce equal yields. These early season deficits suggest N limitation may have occurred, especially in the early season. On the other hand, potentially mineralizeable nitrogen (PMN) assessments on soils sampled before wheat seeding showed that some sites showed variable but significantly higher PMN values after LGF treatment (PMN 3 sites: 12-38 kg/ha over fallow values). This also suggests late season mineralization of LGF residues may have occurred, possibly benefitting wheat during grain fill. Delayed N release may only show as increased wheat grain protein though, as has been commonly observed in plot studies. This also may indicate that substantial N benefits may not be immediately realized after one rotation, but rather over several rotations, as has been suggested by long-term plot scale studies in this region.

- Although we do not have grain yield data yet, preliminary data on total wheat biomass yields (straw and grain combined) showed equal to slightly lowered (total biomass yield loss, two sites: range = 9 - 12%, median = 11%) yields after LGF crops compared to summer fallow.

- No clear preliminary indications of economic benefits from LGF treatment have been worked out from this study, but we suspect seed cost for LGF crops may be a principal factor working against LGF management compared to summer fallow.

- Assessments to date suggest that barriers to LGF adoption may include: seed costs for LGF crops, conflicting spring wheat and LGF crop seeding windows, adherence to first-flower termination timing, herbicide choice for LGF termination and lack of substantial immediate LGF yield benefits compared with summerfallow.

Results of the study as of November 2010 are comprehensively summarized in the poster attached.

Impacts and Contributions/Outcomes

In November 2010 this project was presented in a poster session at the ASA/CSSA/SSSA annual international meetings in Long Beach, CA, which had nearly 4,000 attendees. The project was also presented to a group of ~40 dryland wheat producers and stakeholders at the Sage Creek Watershed Group’s annual field day in August 2010 held in north-central Montana.

The study thus far shows potential to illustrate the agronomic viability of LGF practices under a farmer-managed setting. The economic viability is yet unevaluated. To date, this project has also been very informative to understanding adoption dynamics and potential barriers to adoption of LGF crops as summer fallow replacements. The final results of this study are therefore showing considerable promise to help elucidate the viability of this practice in this substantially important wheat-growing region of Montana. We also anticipate that using a short film of the producers' experiences will be a powerful new outreach tool for MSU extension to present farmer participatory research to stakeholders and to increase adoption trends and future research collaborations. Anticipated completion of this project is late spring of 2011. We will then begin to disseminate results in peer-reviewed journals, extension materials and in presentations to grower associations and students at Montana State University.