Using Crop Diversity in No-till and Organic Systems to Reduce Inputs and Increase Profits and Sustainability in the Northern Plains

Final Report for SW01-048

Project Type: Research and Education
Funds awarded in 2001: $157,888.00
Projected End Date: 12/31/2004
Matching Non-Federal Funds: $21,696.00
Region: Western
State: Montana
Principal Investigator:
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Project Information


A major deterrent to adopting no-till or organic crop production in the Northern Great Plains is concern about weed management problems during the transition from conventional systems and moisture conservation associated with crops as alternatives to fallow. We conducted plot experiments and farm comparisons and found that productivity was reduced in diversified no-till and organic systems, but weed populations were discouraged and costs of inputs reduced in the alternative systems. Net returns were greatest on average for the organic system with organic price premiums, and the no-till reduced-input systems were similar to conventional systems.

Project Objectives:
  1. 1. Understand weed dynamics to predict species shifts within organic and no-till production systems.
    2. Determine crop performance and water use efficiency within organic and no-till systems.
    3. Quantify input levels and costs for organic and no-till systems, including both purchased and operator supplied inputs.
    4. Quantify profitability (net return) of organic and no-till systems.
    5. Educate producers on potential benefits of organic and no-till systems through dissemination of research results.

The predominant small grain cropping system of the Northern Great Plains has utilized a crop fallow rotation under an assumption that the fallow period is required for moisture conservation. The risk of soil moisture loss by removing fallow periods with crops such as legumes into crop rotations in the Northern Great Plains has been thoroughly investigated (Zentner et al. 2001). More sustainable agriculture systems may include the use of reduced tillage, more diversified, and organic cropping systems that minimize off-farm purchased inputs, but may represent increased threat from weeds (Derksen et al. 2002). The transition to more sustainable systems represents a challenging step for producers and requires prediction of how crops and weeds will perform (Maxwell, 1999). Understanding weed population dynamics in response to more sustainable agricultural systems is critical to implementation of these systems on the Northern Great Plains (Davis and Liebman, 2003; Peairs et al. 2005). There has been limited ability to predict the economic density thresholds or distributions of weed populations that require management. In addition, in order to get farmers to tolerate some level of weeds it is critical to predict the future threat that unmanaged populations represent. Adoption of more sustainable systems that reduce purchased inputs and tillage was lagging due to lack of comparative economics among systems (Robertson and Swinton, 2005).

Over the past decade, numerous studies have been conducted to examine the effects of crop rotations on weed populations (Bàrberi et al. 1997; Ball and Miller 1993; Blackshaw 1994; Kegode et al 1999; Liebman and Dyck 1993). However, few studies have investigated the role of input levels and crop sequences within rotations on weed management specific to the NGP region (Thomas et al. 2001). Even less research has separated the effects of crop diversity and associated weed management practices on weed population dynamics (Doucet et al. 1999). The overall goal of this study was to quantify the temporal population dynamics of key weed species during the transition period from a cropping system with little crop diversity managed with tillage and high levels of off-farm inputs to a diversified no-tillage cropping system with reduced levels of off-farm inputs. The specific objectives were to assess the effects of crop rotation, and crop sequence within rotations, coupled with management intensity (input level) on weed population temporal dynamics by quantifying changes in weed seedling densities over time.

A large-scale experiment was established at Moore, MT (Table 1) to compare reduced input no-till and organic systems to conventional small grain production systems. A similar systems experiment was established at Bozeman, MT (Table 2). The goal was to evaluate farm profitability and sustainability within a system that increases crop diversity and reduces off-farm inputs. Thus we quantified production, profitability, and weed population dynamics among the production systems in the experiments at each site and on farms in north central Montana.


Click linked name(s) to expand/collapse or show everyone's info
  • Dave Bushane
  • Chuck Merja
  • Perry Miller
  • Bob Quinn


Materials and methods:

In 1999, a large-plot (96' X 100') no-till crop rotation study was initiated near Moore, MT, with the primary goal of studying weed population dynamics and cropping system productivity in response to crop diversity, rotation and a range of input levels. Each rotation was split into two management schemes, conventional and reduced input, to investigate the potential of enhancing cropping system profitability and sustainability. One rotation was additionally split to include an organic system to provide a comparison to conventional and reduced input no-till systems (Table 1). Detailed measurements of cropping system productivity and weed population dynamics were conducted from 2000 to 2003 to monitor the transition period from conventional management to no-till and organic systems. Geo-referenced 1-m2 circular patches of wild oats, Persian darnel, pigweed, and lambsquarters were established to permit the simultaneous study of weed dispersal and weed population dynamics in response to cropping system management. In addition, a background infestation of downy brome, field pennycress, and other mustard species exists on the site and will be monitored.

The Moore site is located at an elevation of 1281 m and the mean annual temperature is 5.5° C. Limiting resources for crop production in the area were soil type and annual precipitation. Average annual precipitation at the location is 350 to 400 mm with approximately 50 % of the total occurring during the months of May to July. Over the duration of this study, precipitation during these three months was well below normal ranging from 10-45 % below 50 yr averages. A more typical precipitation pattern for this location occurred only during the spring and summer of 2001. The soil type at the experimental site was a Judith clay loam with moderate slopes of 4 to 8%. The soil type is a typical Mollisol found in Montana on high elevation benches and terraces and is productive, but tends to be shallow to gravel. The site was well drained and crop growth can be subject to drought stress during the growing season. Conversely, because of the shallow nature of the soil profile, adequate soil moisture recharge can generally be expected over months when crop growth is not present in the field (personal communication, Dave Wichman).

Objectives 2 and 3 were accomplished with research trials on the Bob Quinn farm near Big Sandy, MT, and Merja Bros. Farms near Sun River, MT, respectively. The on farm experiments utilized field scale equipment. The producer participants were essential in the development of the questions surrounding objectives 2 and 3. The treatment structure was developed through collaboration of local conventional and organic small grain producers and Montana State University-Agriculture Experiment Station staff and researchers.

The framework for study of weed population dynamics within the overall design of the experiments described above was established in late September 1999. Within every split plot of the above rotations two sets of weed subplots were established. Both sets consisted of the same four weed species with one set of plots established inside the main body of the plot and the other set positioned in an untreated check strip with dimensions of 3.3 m by 7.3 m. The four weed species established were redroot pigweed, common lambsquarters (Chenopodium album), Persian darnel (Lolium persicum), and wild oat (Avena fatua). The four species were chosen for the study because visual observations and soil seed bank samples taken during the summer of 1999 at the beginning of the study before weed seeds were planted indicated that there were very low background populations of these species present at the site, but they are common in the region. Greenhouse germination methods were used to quantify the number of viable seeds in the soil cores obtained from the site (Ball and Miller 1989; Forcella 1992). Values of less than 1.0 seeds m -2 of wild oat and 5 seeds m-2 of pigweed were quantified for the site. No seeds of common lambsquarters or Persian darnel were found in the 1999 soil core samples taken from the site. On the basis of these results, each species was established in separate 0.84 m2 plots. The weed sub-plots were established by planting each of the four weed species at a density of 600 seeds m-2 by scattering the seed on the soil surface and gently raking. These plots were permanently marked by staking two corners of each plot with fluorescent polypropylene “road markers” attached to a spike and driven into the ground to a depth of approximately 10 cm.

Enterprise budgets were developed for both the organic and no-till rotational systems described previously. The organic and no-till enterprise budgets were compared with one another and also with enterprise budgets for the conventional rotation. In addition to information from the producer-managed field trials and the large plot rotation studies, the comparisons were drawn on USDA statistics (Montana State Department of Agriculture, 1999-1999 and United States Department of Agriculture, 1990-1999) and regional enterprise analysis efforts (e.g., Johnson et al., 1997ab, Baquet et al., 1998). Budget components of particular interest include input costs (e.g.; fertilizer, fuel, seed, and herbicides), crop revenue, and labor and management requirements.

Organic and no-till producers were interviewed to evaluate their cropping systems, costs and returns over a period corresponding to the plot experiments described above. These producers were selected based on the following criteria, in addition to their willingness to participate:

1. the producers have been in either an organic or a no-till rotation for a long period of time, not less than 8 years;

2. the producers were located in an important cropping area in North Central and Central Montana of approximately 100 miles in radius. This area is roughly east of Ft. Benton, South of Havre, West of Malta, and North of Lewistown;

3. the producers were of a scale comparable to most commercial producers in Montana, farming over 1500 acres for the organic producers and over 2500 acres for the no-till producers;

4. the producers had maintained detailed records adequate for survey purposes, allowing returns estimates from crop year 1998/99 to present;

5. the set of organic producers correspond with the set of no-till producers in terms of the management ability.

These five criteria limited the set of potential cooperators considerably. Three organic producers matched these criteria, and three no-till producers were subsequently identified to roughly match these organic producers in terms of their (admittedly subjectively assessed) management ability. Both sets of producers are viewed locally and statewide as progressive and outstanding farmers. These producers are largely the “cream of the crop” in terms of their success in these rotations and are early adopters.

Research results and discussion:

The period of this project spanned a significant drought in Montana with every year averaging 2-3 inches of precipitation below the previous 30-year average. Thus, it was a significant challenge for proposed diversified systems that remove fallow periods to perform well. In general, the high input systems consistently provided greater crop productivity, but this response was much greater when moisture was less limiting. At the driest sites there was little crop productivity advantage of high input systems over low input or organic systems. Weed population growth rates were generally reduced in diversified and organic systems relative to high and medium input systems with little crop diversity. Economic net returns from the organic rotation with premiums were consistently higher than those for the competing rotations, largely due to the reduced herbicide and fertilizer inputs. The importance of the organic premiums is clearly shown by the differences in the net returns for the premiums case vs. the no premiums case in the organic protestations. The spring wheat based and the diverse no-till rotations provide the highest average returns of the remaining rotations.

The objective of the weed component of this study was to achieve a greater understanding of the temporal and spatial dynamics of the newly established (planted) weed populations in response to crop rotation, crop sequence within rotations, and input levels. It was evident that crop rotation and associated weed management practices (input levels) in the herbicide treated weed populations played a role in the significant differences observed in seedling densities for both species between systems and over time (Table 3).

These findings were similar to that of Liebman and Dyck (1993) who concluded that crop rotations made up of crop species of varying types with varying management practices could be effective weed management tools. We found that independent of input level (conventional, reduced, or organic), increased crop diversity in crop rotations and including fallow years, whether managed chemically or through the use of a green manure crop, had the effect of suppressing the density and spatial extent of all the weed species populations that we studied. However, chemical weed management practices within both the conventional and reduced input rotations in this study were the major management factor driving weed population dynamics. The range of weed management options that a diverse crop rotation affords can be tailored to meet the specific needs of land managers to address a specific weed management concern. For example in this study, management of wild oat, which is notoriously difficult to control in continuous small grain/fallow rotations in the NGP, was significantly improved through the addition of the dicot crops to the alternative rotations in this study. This allowed for the use of effective herbicide applications in the dicot phases of the rotations that negatively impacted the wild oat populations. The benefit of crop rotation, from a weed management perspective, is the ability that it gives growers to develop a weed management plan that enables them to use alternative weed management strategies and practices that target a specific weed species or life history stage of a particular weed species (Anderson 2004).
Conversely, crop rotation in the absence of chemical weed management played a much smaller role in the dynamics of the weed populations in the untreated areas of this study. This finding is similar to those of other studies (Davis and Liebman 2003; Doucet et al. 1999; Légère et al. 1997; Thomas et al. 1996), where crop rotation and crop sequence played a relatively small role in influencing weed density when decoupled from corresponding weed management practices. This represents a significant hurdle in encouraging adoption of low input and organic production systems. It is also indicative of the further research needed to develop optimum weed management practices in these systems. The cultural weed management practices utilized in this study, such as delayed crop planting and increased crop seeding rates, in the absence of chemical weed managements practices did not reduce the densities of either wild oat or redroot pigweed in this study. Even if weed densities were held at a low equilibrium with cultural practices, the populations had high enough densities to have a significant potential to increase without the added mortality from herbicide applications. If chemical weed management inputs are to be reduced, even more cultural mechanisms need to be introduced to suppress weed populations to levels acceptable by conventional producers.
Results of this study also suggest that initial starting point or entry point into the rotation can have a profound influence on the dynamics of the weed population over the period of a rotation. For example, when a wild oat population was established in the herbicide-tolerant canola phase of the reduced input alternative crop rotation, this population decreased dramatically after the establishment year and as a result was lower over the duration of the rotation compared to when a population was established in spring wheat phase of that same rotation. This highlights the importance of having an in-depth understanding of the potential effects that a particular crop sequence may have on a given weed population. Crop rotations are critical for breaking up weed life cycles and reducing populations, but starting weed population densities and the first crop encountered may determine the success of any given rotation.
The results of this study underscore the importance and power of long-term cropping system studies, however difficult or costly they are to manage and maintain, to determine the effect of past management history on future weed population temporal dynamics. This study also highlights the need for continued investigation into ecologically based weed management strategies as optimization of reduced-input systems continues across the region. A powerful finding of this study was that weed populations in systems that rely on more integrated methods of weed control coupled with a reduction in off-farm inputs (herbicides) could be successfully managed. In the reduced-input systems, crop diversity in rotations and associated management practices facilitated the management of the wild oat and redroot pigweed in this study when herbicide inputs were reduced compared to inputs in the conventional systems, but even the reduced-input systems remained reliant on chemical weed management practices.
The results suggest that it is possible to mange specific weed problems with an understanding of the interplay between crop rotation, crop sequence, and input level. Undoubtedly, this will require more time and energy on the part of the grower to be put into crop and weed management tasks. However, if the current trend towards the development of low input cropping systems continues, there may well be incentives, both economic and environmental, for the grower to manage according to low input objectives. The risk of adopting a similar cropping system to one of the alternative systems described here and managing it with a given level of inputs is dependent on a wide array of production factors specific to individual growers. We have demonstrated, however, some positive weed management attributes of the cropping systems in this study that may be further fine-tuned as part of an individual’s crop production strategy. This will enable a grower to develop crop rotation strategies with a given level of inputs facilitating the design of a suite of weed management tools that are both effective and profitable.

Accomplishments and Milestones:

The first important accomplishment of this project was to further demonstrate that diversified cropping systems can be successful even under the drought conditions encountered over the course of the study. Water use efficiency was generally increased with the reduced-input diversified systems over the conventional wheat/fallow system.

It is clear from this study that more diversified crop rotations can improve weed management in reduced-tillage small grain production cropping systems. We found, however, that reliable weed mortality offered by herbicides is important to add to the less reliable (higher risk) weed suppression offered by cultural weed management practices. Variability in weed population response to cultural practices emphasizes the requirement to express these results as general principles rather than as prescriptions of specific rotations or weed management practices. Certainly, within the range of weed population variation in response to these systems, it is possible that the weed species that we studied could be managed with reduced or even no herbicide inputs. Thus, there may be sites or years where, under particular crop rotations and sequences, these reduced cost systems could be implemented with minimal risk of future weed management problems. However, site-specific and improved knowledge of weed behavior in response to cultural practices will be crucial for risk reduction. This is an important accomplishment because it emphasizes the risk associated with transitioning to new systems and has made it clear that those who embark on a transition to reduced inputs and/or organic systems must be cognizant of the influence of past cropping sequences and weed populations. In addition, prescriptive approaches to transitioning to new systems are not possible.

This study compared gross return, production costs, and net returns for organic, no-till, and conventional production systems. The comparison was uniquely carried out for both plot studies and for producer case studies, all for multiple years. The study also includes both a period of relatively normal rainfall and a period of drought in a dryland production system. The organic producers changed their rotations and tillage practices considerably in response to drought; the no-till producers changed their activities less. The net returns from the management systems evaluated showed both the no-till and the organic rotations to have superior net revenues to more conventional rotations as measured by county averages. Organic production had higher net returns per acre than the no-till rotations did, but these organic rotations appear to require higher labor and management hours than the no-till rotations do. That is, organic producers seem to trade off higher labor and management time per acre for higher returns per acre.

Research conclusions:

The predominant small grain cropping system of the Northern Great Plains has utilized a crop fallow rotation under an assumption of moisture conservation. More sustainable systems may include the use of more diversified and organic systems that reduce inputs. The transition to more sustainable systems represents a challenging step for producers and requires prediction of how crops and weeds will perform. Weed population dynamics in response to more sustainable agricultural systems on the Northern Great Plains is critical to implementation of these systems. This study has already begun to show significant differences in weed behavior under different crop management and promises to allow prediction of weed responses to a wide range of management approaches from organic to high- input conventional. To our knowledge, there are no other studies that have simultaneously measured spatial and temporal dynamics of weed populations. Thus, there has been limited ability to predict the economic thresholds or distributions that determine optimum weed management under most conditions.

Evaluation surveys of recent farm conferences in Montana highlight strong producer interest in diversified crop rotations. Pulse crops (pea, lentil, chickpea) are featured prominently in this research project and pulse crop acreage in Montana jumped dramatically to 350,000 acres in 2005, due in part to the contributions of this research project. This has meant an important new source of income for Montana farmers. This research project continues to investigate optimal agronomic practices for alternative crops so inclusion in cropping systems will have a greater chance of being successful. Rotation studies address longer term questions related to water use efficiency and soil quality.

Results of this study reinforce the importance of why crop rotation diversification has long been acknowledged as a crucial practice in any type of integrated weed management plan and also why more diverse crop rotations in the NGP should be promoted, assuming specific other crop production factors can be resolved.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:

Direct Communication With Farmers:

Bruce Maxwell poster presentation: Using Crop Diversity in No-till and Organic Systems to Reduce Inputs and Increase Profits and Sustainability in the Northern Plains. AERO Organic Training and Conference / Montana Organic Organization Dec 5, 2003, Great Falls, MT
Perry Miller poster presentation: Increasing crop water-use efficiency in advanced no-till systems. AERO Organic Training and Conference / Montana Organic Organization Dec 5, 2003, Great Falls, MT

Alternative Agriculture Farm Tour. Co-sponsored by: NRCS and AERO. Floweree, MT. June, 2003.
Maxwell presentation on weed seed banks in CRP. MABA. Great Falls, MT, Jan. 2004
Results from experiments were presented by Drs. Maxwell and Miller at a Field Tour at the Post Agronomy Farm near Bozeman, MT in 2004 and 2005.

Hulting reported results summary to the AERO Agricultural Task Force meeting in Oct. 2003.

Buschena and Maxwell participated in Transition to Organic Workshops at Malta and Great Falls, MT in February, 2005, sponsored by AERO.

Maxwell and Miller participated in Transition to Organic Workshop at the Montana Organic Growers Association meeting in November, 2005.

Maxwell and Miller have participated in the 2005-2006 NCAT phone conference sessions to educate NRCS farm program people about the use of diversified, low-input and organic systems.

Peer Reviewed Journal Papers, Chapters, Theses:

Hulting, A.G. 2004. Weed population dynamics in diversified cropping systems of the Northern Great Plains. Ph.D. Thesis, Department of Land Resources and Environmental Science, Montana State University. Pp. 144.

Maxwell, B.D. and L.C. Luschei. 2005. Ecological justification for site-specific weed management. Weed Science 53:221-227.

Maxwell, B.D. and E. Luschei. 2004. The ecology of crop-weed interactions: Toward a more complete model of weed communities in agroecosystems. Journal of Crop Improvement 11:137-154.

Maxwell, B.D. and E. Luschei. 2004. The Ecology of Crop-Weed Interactions: Toward a More Complete Model of Weed Communities in Agroecosystems. pp. 137-152. In D.R. Clements and A. Shrestha (eds), New Dimensions in Agroecology. Hawthorn Press.

Wagner, N., B. Maxwell, L. Rew, and D. Goodman. 2002. Development of a yield prediction model for site-specific management of herbicide and fertilizer. Proceedings of the 6th International Conference on Precision Agriculture. Minneapolis, Minnesota. July 14-17.

Miller, P.R., and J.A. Holmes. 2005. Cropping sequence effects of four broadleaf crops on four cereal crops in the northern Great Plains. Agron. J. 97:189-200

Nielsen, D.C., P.W. Unger and P.R. Miller. 2005. Efficient water use in dryland cropping systems in the Great Plains. Agron. J. 97: 364 372.


Clayton, G., P. Miller, Y. Gan, R. Blackshaw, P. Carr, B. Gossen, K.N. Harker, G. Lafond, J. O'Donovan, O. Olfert. 2005. Ecological pulse crop management. In (CD-ROM) Agronomy Abstracts ASA, CSSA, SSSA, Madison, WI.

Hulting, A.G., A.J. Bussan, B.D. Maxwell and P. Miller. 2001. Weed population dynamics in diversified cropping systems of the northern plains. West. Soc. Weed Sci. Proc. 54: Coeur d’Alene, ID, March, 2001.

Hulting, A.G., A.J. Bussan and B.D. Maxwell. 2002. Development of a spatial simulation model for evaluating potential patterns of spread of an invasive grass in a diversified cropping system. Weed Sci. Soc. Am. Abstracts 42:62.

Hulting, A. G., B. D. Maxwell, and A.J. Bussan. 2002. Spatial pattern and rate of spread of Persian darnel and wild oat in a diversified cropping system. West. Soc. Weed Sci. Proc. 55:27. Salt Lake City, Utah

Hulting, A.G., B.D. Maxwell, A.J. Bussan, P.R. Miller. Can the processes that determine weed metapopulation spatial patterns be identified? WSSA Abstracts 43:44, Jacksonville, FL. Feb. 2003.

Jones, C.A. and P.R. Miller. 2005. Soil fertility differences in diversified no till and organic rotations following a 4 yr transition. In W.B. Stevens (ed.) Western Nutrient Management Conference Proceedings. 6:94 99. Potash and Phosphate Institute. Brookings, SD.

Maxwell, B., A. Hulting, C. Repath and L. Rew. Linking spatial and temporal dynamics to estimate invasiveness of non-indigenous plant populations. The Ecological Society of America Conference August 1-6, 2004 Portland, OR. p88.

Maxwell, B.D. and L.C. Luschei. Ecological justification for site-specific weed management. WSSA Abstracts 44:69, Kansas City, MO. Feb. 2005.

Maxwell, B.D. (2005) Assessing the relative role of competition and dispersal in determining the dynamics of plant populations in agroecosystems. Ecol. Soc. of Am. Ann. Meeting, Montreal, Canada, August, 2005. p 110.

Miller, P., J. Holmes, D. Buschena, and C. Jones. 2005. Comparing low and high input strategies in diversified organic and no till cropping systems. Crop Sci. Soc. Am. Summer Mtg., Bozeman, MT, 19-22 June. Abstract on CD-Rom.

Miller, P., K. McKay, C. Jones, S. Blodgett, F. Menalled, J. Riesselman, C. Chen and D. Wichman . 2005. Growing dry pea in Montana. Montana St Univ Ext Serv Montguide MT200502 AG. 8 p.

Miller, P., D. Wichman and R. Engel. 2005. Sequencing annual legume forage before wheat to increase water use efficiency in no till systems in the northern Great Plains. In (CD-ROM) Agronomy Abstracts ASA, CSSA, SSSA, Madison, WI.

Pollnac F, Maxwell BD, Menalled F. (2005) Preliminary observations of the species area curve in organic and conventional spring wheat systems. Western Society of Weed Science, Vancover, Canada, March 2005. p 14.

Walley, F.L. G. Clayton, P. Miller, P.M. Carr, and G. Lafond. Nitrogen economy of pulse crop production in the northern Great Plains. In (CD-ROM) Agronomy Abstracts ASA, CSSA, SSSA, Madison, WI.

Education and Outreach Outcomes

Recommendations for education and outreach:

Areas needing additional study

We are currently communicating with AERO to seek more funding for workshops relating to transitioning to organic or low-input farming practices. The model that we used in 2005 was highly successful with a large proportion of the farmers in attendance doing some kind of adoption in the growing season following the workshops.

We are developing an MSU extension bulletin on transitioning to organic production that we hope will reduce the potential failures due to choice of lands (primarily CRP) that accommodate immediate organic certification, but may be very risky with regard to high weed seed banks and dead soils.

The most critical research needs include development of methods for farmers to locally parameterize weed population dynamic models that will aid them in identifying future weed problems. Clearly, our research has shown that weed population demographics are highly site specific and erratic during the transition years. Therefore, some mechanism that encourages on-farm research or automated data retrieval (e.g. precision agriculture technology) through policy or just ease of use will accomplish a major hurdle in the adoption of more sustainable systems. Research should be directed at creating and testing methods on farms to quantify weed impacts and population dynamics under an adaptive management paradigm.

Extending the time for the economic analysis to span more average and high precipitation years, would likely prove quite valuable. Such a longer-term study would help to address questions regarding the long-term nature of these systems and their profitability.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.