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Dep. of Plant Sci., Univ. of Manitoba, Winnipeg, MB, Canada R3T 2N2
* Corresponding author (rene_van_acker{at}umanitoba.ca).
Received for publication November 18, 2002.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONNOTESMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Abbreviations: MAF, Manitoba Agriculture and Food • MCIC, Manitoba Crop Insurance Corporation • NGP, northern Great Plains • PFP, Pesticide Free Production
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONNOTESMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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In response to the limited success of currently available frameworks for pesticide use reduction, Manitoba farmers, researchers (University of Manitoba; Agriculture and Agri-Food Canada in Brandon, MB), and extension workers [Manitoba Agriculture and Food (MAF)] developed Pesticide Free Production (PFP)1 in 1999. Pesticide Free Production is a flexible, simple framework that is intended to appeal to a broad range of farmers. Pesticide Free Production crops are defined as crops that are not genetically modified and have not been treated with pesticides from the time of crop emergence until the time of marketing. Such crops cannot be grown where residual pesticides are considered to be commercially active (Pesticide Free Production Canada, 2002). These guidelines prohibit the use of in-crop pesticides and seed treatments for one crop year. Prior use of pesticides is permitted only if the product is considered not to have active residual at the time of PFP crop seeding, as indicated by the manufacturer's recropping restrictions. Synthetic fertilizer use is permitted, as is a pre-emergent application of a nonresidual pesticide such as glyphosate [N-(phosphonomethyl)glycine]. Pesticide Free Production may be a means to draw mainstream farmers to explore integrated approaches to pest and crop management. It may also provide the opportunity for a marketable PFP food product label (Magnusson, 2002).
In the NGP, weeds are major pests, and herbicides represent approximately 85% of pesticides used (Derksen et al., 2002). A commonly cited constraint for herbicide use reduction is the potential for escalating weed populations and yield reduction in future years (Czapar et al., 1997). Yields of organically produced crops are commonly, but not always, reduced from conventional yields (Lockeretz et al., 1981; Stanhill, 1990). A broad range of weed control methods are used in reduced-pesticide cropping (Bond and Grundy, 2000). In particular, biologically robust cropping systems that are less susceptible to weed proliferation and competition may allow for herbicide use reduction (Van Acker et al., 2001).
The adoption of reduced-pesticide practices is related to a number of factors, including the implementation of agronomic management practices to allow for reductions in pesticide use as well as farmer demographic and attitudinal characteristics (e.g., Constance et al., 1995; Egri, 1999; Duram, 1999). For the purposes of this paper, discussion is restricted to the importance of agronomic management. The importance of demographic and attitudinal characteristics in the adoption of PFP is explored in more detail elsewhere (Nazarko et al., 2003).
We hypothesized that adoption of PFP is related to factors that allow for increased ability to manage for pesticide reduction (such as smaller farm or field size and detailed field history record-keeping) and the implementation of agronomic management practices that provide pest suppression [such as the use of diverse crop rotations (particularly forages), production of livestock to utilize forage crops, and specific seeding, herbicide, and tillage practices].
The objectives of this study were to (i) evaluate the potential of PFP to be widely implemented on typical farms in Manitoba and (ii) assess the level of success farmers experienced with PFP. The first objective was accomplished by documenting the agronomic and demographic characteristics of fields and farms that participated in an on-farm PFP pilot project and comparing them with indicators of typical agronomic practices and demographic characteristics in this region. If these are found to be typical, it suggests good potential for wide adoption of PFP. The second objective was accomplished by assessing the yield, pest levels, grade and dockage characteristics, and farmer satisfaction related to PFP crop production. If PFP crops can be produced without excessive yield or quality loss, with high levels of farmer satisfaction regarding residual weed densities resulting from PFP, and high levels of farmer interest in continuing the practice, then its implementation can be considered successful.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONNOTESMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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During the first year of the project (2000), all volunteered grain crop fields in Manitoba were included. Fields sown to forage, silage, or greenfeed crops were not included, but cereal crops for which the end use (forage vs. grain) was uncertain were included. Fields in transition to organic certification were included. In 2001, there was sufficient interest in PFP that the focus of the study was narrowed to include only those crops showing high levels of farmer interest [wheat (Triticum aestivum L.), oat (Avena sativa L.), barley (Hordeum vulgare L.), and flax (Linum usitatissimum L.)].
Field Survey
In-crop weed densities were assessed before the normal timing of postemergent herbicide applications. Weed densities were assessed in 20 0.1-m2 quadrats, representing as much of the field as possible. In cereal crops, leaf rust and leaf-spotting disease complexes were assessed in a manner similar to that used by the Canadian Plant Disease Survey (Gilbert et al., 2001). The percentage disease coverage on the flag leaf in wheat and oat, and the penultimate leaf in barley, was determined at the milk- to hard-dough stage in 20 locations in each field.
In flax and cereal crops, aphid (Homoptera, various species) and grasshopper (Orthoptera, various species) levels were assessed. In wheat fields, orange wheat blossom midge (wheat midge; Sitodiplosis mosellana Gehin) levels were also assessed. In cereals and flax, the number of aphids on the main stem was counted at 20 locations in each field. The economic threshold for cereals is 12 to 15 aphids per main stem before the soft-dough stage; for flax, it is three per main stem before flowering and eight per main stem at the green boll stage (MAF, 2002). Grasshoppers were counted in 20 1-m2 locations in each field. The economic threshold for cereals and flax is 8 to 12 grasshoppers m-2 (MAF, 2002). Wheat midge levels were assessed by a method that allowed for consideration of fields at various crop stages located throughout a large geographic area. At the early grain-filling stage, 20 heads were collected from each field. Ten kernels per head were examined for the presence of wheat midge larvae. The economic threshold is approximately 6 to 10% of kernels per head infested (John Gavloski, MAF provincial entomologist, 2002).
Grain samples from fields that achieved PFP certification were mailed in by participants after harvest. Grading of samples and dockage assessments were completed by the Canadian Grain Commission (Winnipeg Service Centre, Winnipeg, MB).
Questionnaire Design
After harvest, all participating farmers were asked to complete a detailed questionnaire regarding field history and demographic information. Questionnaire design met University of Manitoba ethics requirements and was based on guidelines and discussion provided by Sudman and Bradburn (1982), Jackson (1988), and Babbie (1990). The questionnaire was pretested on 10 subjects with farming backgrounds and was modified where required. Questionnaires were mailed to farmers and were returned by mail throughout the winter. Unanswered and unclear responses were clarified through telephone interviews.
Another questionnaire was used to follow up with farmers who had produced certifiable PFP fields, conducted via telephone 1 yr after harvest of the PFP crop. Open-ended questions were used to elicit responses about weed densities the year after PFP.
To provide information comparing the demographic characteristics of PFP participants with typical Manitoba farmers, an additional questionnaire was conducted by a professional polling company with significant agricultural experience (Ipsos-Reid Corp., Winnipeg, MB) in February 2002. A stratified random sample of 154 farmers, with proportions representing the population distribution in each Manitoba census district, was used. A telephone survey was used to minimize self-selection of respondents. Respondents were restricted to farmers with more than 130 ha of seeded cropland. The margin of error for this survey was ±8% at the 95% level of confidence. The refusal rate was 30.3%, which is within the normal range for agricultural surveys conducted by this company.
Data Analysis
Fields and farmers were categorized into three groups, representing different levels of pesticide use reduction in the year PFP was attempted. Initially, fields were divided into two groups based on whether or not the field met PFP certification requirements. Those fields that met certification requirements were further subdivided into two groups based on whether or not the field was in transition to organic certification. The three groups were considered ordinal. Classification was not based on an objective determination of the success of a field in terms of pest pressure but more appropriately on the farmer's ability to meet PFP certification requirements. The three groups of fields were as follows: fields that were (i) not certifiable as PFP (referred to as noncertifiable fields), (ii) certifiable as PFP but were not in transition to organic certification (certifiable, nontransitional fields), and (iii) certifiable as PFP and were in transition to organic certification (certifiable, transitional fields). Farmers were categorized into three groups comparable to the field-based groupings: farmers with (i) no certifiable PFP fields (farmers without certifiable fields), (ii) certifiable PFP fields whose farms were not in transition to organic (farmers with certifiable fields, nontransitional farms), and (iii) certifiable PFP fields whose farms were in transition to organic (farmers with certifiable fields, transitional farms). If farmers participated in both years, duplicate values for farmer-based variables were removed, so each farm was included only once. When considered together, the noncertifiable and certifiable, nontransitional groups are referred to as the conventional groups. It should be emphasized that the noncertifiable designation does not necessarily imply typical Manitoba fields or farmers. In fact, two fields in the noncertifiable group were in transition to organic but were not certifiable as PFP because a soil residual herbicide had been used previously.
Before analysis, we determined that observations would be combined across the 2 yr of the study. The rationale for this approach was the inherent diversity of the fields and farmers involved, which may have allowed for the distinction of groups based on several criteria, such as soil type, tillage system, or year. Given the relatively small number of participants, separation of observations by each of these criteria would have resulted in groups so small as to prohibit meaningful comparison. The maintenance of one data set provided a broad description of farmers and fields involved in this exploratory study. Grade distribution and dockage data were combined across the two certifiable PFP groups to present a general indication of these characteristics in certifiable PFP for each crop.
Statistical analysis was performed using SAS (SAS Inst., Cary, NC). PROC GLM was used to perform analysis of variance (ANOVA) for comparisons of continuous numerical variables among groups. Group was the only source of variation included in the model. Fishers Protected LSD was used to separate means. In several situations, data did not meet the assumption of normality, but transformations did not confer normality. In these cases, PROC NPAR1WAY was used to generate Mann–Whitney and Kruskal–Wallis tests, the nonparametric equivalents of two-sample t tests and one-way ANOVA, respectively (Stokes et al., 2000). Pairwise comparisons of groups using Mann–Whitney tests were performed if the overall Kruskal–Wallis test was significant (P = 0.05). In cases where the outcome of a nonparametric test agreed with the outcome of ANOVA (significant or not significant at the P = 0.05 level), the ANOVA result was presented. If data could be transformed to meet normality but results agreed with the outcome of ANOVA on the untransformed data, the results for the untransformed data were presented. PROC FREQ was used to generate contingency tables and chi-square statistics for comparisons of frequencies of categorical data. If tables contained nonordinal response variables, Pearson's chi-square was used to test the null hypothesis of no general association. For tables with ordinal response categories, the Mantel–Haenszel chi-square was used to test for linear response (Stokes et al., 2000). When zero counts were generated in a table, or if more than 20% of table cells had an expected value of less than 5, Fisher's exact test was used (Stokes et al., 2000). Contingency tables were used to generate pairwise comparisons between groups if the overall chi-square test was significant (P = 0.05).
Despite the relatively large number of variables considered in the study, no adjustment was made for increasing risk of type I error. Multivariate analysis of variance (MANOVA) was not an appropriate method of analysis for this study, given its inability to handle categorical and missing data. Because this study depended on farmers to provide information, missing values were common. The Bonferonni technique (Snedecor and Cochran, 1989) was not applied because of its very conservative nature, prohibiting adequate discussion of the results of this exploratory study. Inferential methods are limited in observational studies, and given the conservative context in which this study could be discussed, extremely conservative hypothesis-testing procedures were not necessary.
Data for comparison with results were obtained from government agencies, farmer surveys conducted by various organizations, and peer-reviewed publications. Comparative information for which there was no published source was obtained from appropriate industry representatives.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONNOTESMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Farmers volunteered fields seeded to 16 different crops. Only 11 crops were included because in 2001, specific crops were targeted (only wheat, oat, barley, and flax in 2001) (Table 1). Farmers primarily volunteered spring and winter cereal fields [spring wheat, winter wheat, fall rye (Secale cereale L.), barley, and oat] as well as flax fields. In 2000, soybean [Glycine max (L.) Merrill], buckwheat (Fagopyrum esculentum L.), hemp (Cannabis sativa L.), and canola (Brassica napus L. and B. rapa L.) fields were included. In 2001, a small number of faba bean (Vicia faba L.), alfalfa seed (Medicago sativa L.), corn (Zea mays L.), pea (Pisum sativum L.), sunflower (Helianthus annuus L.), and various forage crop fields were volunteered but not included due to the restriction on crop types in 2001.
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Pesticide Free Production Certification
In total, 2368 ha of the land area involved in the study was certifiable as PFP, representing 83% of the land area and 68% of fields volunteered. The proportion of certifiable fields varied depending on the crop type (Table 1). No canola fields were certifiable due to the use of seed treated with fungicide, insecticide, or both. Seed treatments are used by 95% of western Canadian canola growers [Canola Counc. of Can., 2000]. This may limit the future success of PFP canola. Despite the fact that canola is a major crop in Manitoba, it represented only 4% of fields volunteered in 2000. Only 17% of winter wheat fields were certifiable due to fungicide applications to control leaf diseases. While there is opportunity for herbicide use reduction in winter wheat because it competes well with weeds, current cultivars grown in Manitoba are susceptible to leaf diseases. Given the small acreage of winter wheat in Manitoba [less than 2% of total wheat acreage (Tekauz et al., 2001)], it is noteworthy that 10% of participating fields in 2000 were winter wheat. A high percentage of oat, spring wheat, and barley fields were certifiable (79, 67, and 65%, respectively). All fall rye and buckwheat fields included in the study were certifiable. Fall rye competes well with weeds, partly because of its fall planting date (MAF, 2001). Buckwheat tends to escape competition with early emerging weeds due to its late seeding date in this region, and there are few pesticides registered for use in this crop (MAF, 2001). Because flax is not a good competitor with weeds, the proportion of certifiable flax fields (63%) can be considered relatively high. This can be attributed in part to the fact that half of the flax fields involved in this study were in transition to organic or underseeded to forage species for which there were no herbicides registered. Farmer satisfaction with the production of PFP flax tended to be lower than for cereals (data not shown).
Field and Farm Size
Field size ranged from 3 to 130 ha, and there were no significant differences in average field size among participant groups (Table 2). Average field size for all groups was somewhat larger than the 21-ha average for randomly selected spring cereal and oilseed crops in Manitoba (Thomas et al., 1999) and the 17.6-ha average for organic farms in the NGP (Entz et al., 2001). This suggests a willingness on the part of participants to experiment with pesticide use reduction on a relatively large scale.
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Crop Yields
There were no significant differences in average crop yields among groups. Average yields for all three groups were moderately lower than both the 10-yr and the same-year yield averages based on comparison with each cultivar and crop insurance risk area (Table 3). Average yields in all three groups may have been reduced from baseline yields because some farmers tended to select their less productive fields for PFP attempts (personal observation). This is consistent with the concept of initially implementing new practices in a low-risk fashion (Rogers, 1983). Yields of crops from all three groups were different (P = 0.075) when compared as a proportion of long-term organic yield averages in the NGP (Entz et al., 2001) (Table 3). Both conventional groups had yields more than 30% higher than organic averages.
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Grade and Dockage Characteristics of Certifiable Pesticide Free Production Grain
Grades of certifiable PFP grain (Table 4) tended to be lower than those typical for Manitoba [Manitoba Crop Insurance Corporation (MCIC), unpublished data, 1992–2000] (data not shown). The most common downgrading factors for certifiable PFP grain were low hectoliter weight for oat (especially in 2001) and Fusarium head blight (Fusarium spp.)–damaged kernels for spring wheat. Neither of these is directly attributable to non-use of pesticides. Currently, registered fungicides in Canada only provide suppression of Fusarium head blight (MAF, 2002), and cereals with low hectoliter weight were common throughout Manitoba in 2001 (Agric. and Agri-Food Can., 2001). Between 1992 and 2000, less than 1% of Manitoba field crops were downgraded for reasons directly attributable to lack of herbicide use (e.g., inseparable seed or mixed grain due to seed production by weeds or volunteer crops) (MCIC, unpublished data, 1992–2000). Two certifiable PFP grain samples (3.1% of samples) were downgraded for these reasons, and one sample (1.5% of samples) was downgraded due to wheat midge damage (data not shown).
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Pest Levels
Average pre–weed control weed densities in noncertifiable fields were higher (P = 0.065) than both certifiable groups (Table 3). This suggests that farmers were choosing to apply herbicides to fields with the highest weed densities and retain fields with lower densities for certifiable PFP. Average weed densities ranged from 110 plants m-2 (certifiable, nontransitional fields) to 156 plants m-2 (noncertifiable fields). These weed densities were 1.9 times (certifiable, nontransitional fields) to 2.7 times (noncertifiable fields) higher than the average post–weed control densities reported for respective ecoregions by Thomas et al. (1998). However, densities were only 0.58 times (certifiable, transitional fields) to 0.73 times (noncertifiable fields) pre–weed control densities for this region (Friesen and Shebeski, 1960) (data not shown). Weed densities in certifiable fields were similar to or lower than pre–weed control densities found in continuous cereal fields in Manitoba (Ominski et al., 1999) while those in noncertifiable fields were higher. Results suggest that farmers chose relatively weed-free fields (on a pre–weed control basis) for PFP attempts, and of these fields, only those with relatively low weed densities were retained for PFP certification. A higher proportion of farmers with certifiable fields rated the weed density in the field designated for a PFP attempt as light (46%) rather than average, heavy, or very heavy compared with results reported by Thomas et al. (1999) (17%; data not shown). Several authors note increases in weed densities during the transition to organic production as well as in certified organic production (Rydberg and Milberg, 2000; Brandt and Ulrich, 2001). The lack of difference in weed densities between certifiable, nontransitional fields and certifiable, transitional fields may be due to the early stage of transition for most of the certifiable, transitional fields (data not shown).
Weed seed return and escalating weed densities have been cited as a major concern of farmers who are reducing herbicide use (Czapar et al., 1997). Uncontrolled weeds in a given year can result in up to a 14-fold increase in the weed seed bank (Leguizamon and Roberts, 1982); however, crop competition can reduce weed seed return (Lindquist et al., 1995). Participating farmers rated 72% of certifiable fields as having no or only slightly higher weed pressure the year after certifiable PFP compared with what they would expect following a herbicide-treated crop (data not shown). The remaining 28% of fields were rated by farmers as having increased weed densities, which they attributed to herbicide use reduction. Despite this, 83% of farmers with certifiable fields indicated that their regular herbicide program was adequate to control all weed infestations subsequent to the PFP year (data not shown), and very few farmers indicated their intention to increase pesticide use as a result of producing a certifiable PFP crop (Table 2). The fact that most farmers were satisfied with weed control the year after PFP suggests that the efficacy of currently available herbicides is high enough to provide adequate control in cases of increased weed densities following pesticide use reduction. This is consistent with comments made by Buhler (1999), who noted that moderate increases in weed densities did not reduce the level of weed control in subsequent years. In long-term studies (9–10 yr), Swanton et al. (2002) and Bostrom and Fogelfors (2002) found no significant differences in weed densities among reduced-herbicide and conventional treatments. Eliminating herbicide use based on annual field selection and implementation of alternative weed management practices should further reduce the risk of weed population increase. Légère et al. (1996) suggested that the impact of residual weed densities depends on the competitiveness of the cropping system. Similarly, weed seedling and seedbank densities were similar or lower in low-input rotations with varied seeding dates vs. high-input rotations with less variation in seeding dates (Derksen et al., 2002).
Disease pressure was not a concern in most fields (Table 5), except for winter wheat fields. In general, insect pest levels in certifiable fields were below economic thresholds for this region (Table 5). Aphid, grasshopper, and wheat midge infestation levels were not significantly different among groups.
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Crop Rotation
Farmers attempting PFP were rotating among crop types to a similar or greater degree compared with typical farmers in Manitoba. The proportion of fields following the same crop type in rotation was not significantly different among groups and ranged from 25 to 35% of fields (Table 6). In comparison, 39% of spring wheat, 60% of barley, 52% of oat, and 10 to 15% of broadleaf crops grown in Manitoba between 1994 and 1998 followed the same crop type in rotation (MCIC, 2002). The average number of crops grown regularly on a given farm was not significantly different among groups, nor between PFP participant groups and the random sample of Manitoba farmers (Table 2).
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While there is no indication of differences in the use of forages on a whole-farm scale among groups, or between participants and various typical measurements for Manitoba, there is evidence that farmers attempting PFP were more strategic in their use of forage crops to facilitate pesticide use reduction than is typical in Manitoba. The use of forages immediately before a PFP attempt was particularly common among certifiable, transitional fields. Pesticide Free Production was also commonly implemented during forage establishment years. Given the low frequency of forage in typical crop rotations in Manitoba (Thomas et al., 1999; Entz et al., 2002), the proportion of fields intended for forage crop production the year after PFP is relatively high for both certifiable groups.
A higher proportion of farmers in all participant groups were growing winter cereals compared with the random sample of Manitoba farmers (P = 0.052) (Table 2) and with values reported by Statistics Canada (2002). The proportion of farmers stating that they regularly grew winter cereals was not significantly different among participant groups (Table 2). Winter cereals are particularly competitive with weeds (MAF, 2001), and the fall seeding date limits the impact of Fusarium head blight infection compared with spring cereals (Tekauz et al., 2001).
Farmers were asked about their future plans to include PFP crops in rotation. The majority of farmers in all groups were interested in pursuing PFP in a regular crop rotation in the future (80, 93, and 90% of farmers without certifiable fields; with certifiable, non-transitional fields; and with certifiable, transitional fields, respectively). Following harvest, 15% of noncertifiable and 9% of certifiable, nontransitional fields were intended for another PFP attempt on the same field the following year (data not shown).
Use of Tillage and Herbicides
The proportion of fields under reduced tillage (zero or minimum tillage; self-defined by farmer) was significantly different among groups (Table 7). The proportion of reduced tillage among noncertifiable fields and certifiable, nontransitional fields was higher than the Manitoba average (38% of fields) (Thomas et al., 1999). The significantly lower proportion of reduced tillage among certifiable, transitional fields compared with the other two participant groups was not unexpected as tillage can be substituted for herbicidal weed control. However, Liebig and Doran (1999) found that organic farms used less tillage than comparable conventional farms, indicating that reduced pesticide use does not necessarily require higher levels of tillage. It is noteworthy that the level of reduced tillage in the certifiable, nontransitional group was higher than typical provincial levels, indicating that certifiable PFP in the context of conventional production (i.e., not in transition to organic) has been implemented on a relatively high proportion of reduced-tillage fields. Pesticide Free Production may be more appropriate than organic production as a pesticide use reduction strategy for reduced-tillage cropping.
The proportion of fields receiving a pre-seed tillage operation was significantly different among groups (Table 7). A significantly higher proportion of certifiable, transitional fields received preseeding tillage compared with other groups. This proportion was also much higher than the provincial average of 52% (Thomas et al., 1999) and reflects a trade-off between herbicide use and tillage among certifiable, transitional fields. Not surprisingly, none of the certifiable, transitional fields received a pre-emergent or pre-seed herbicide, an outcome that was significantly different from both other groups (Table 7). Pre-emergent applications of nonresidual herbicides are allowed under PFP regulations, in part to accommodate reduced tillage and direct seeding. These practices have become more common in recent years, particularly in Agroecozone 2 (Statistics Canada, 2002). Pre-emergent herbicide applications would be expected to reduce in-crop weed pressure and increase the likelihood of a certifiable PFP crop. A higher proportion of fields in both noncertifiable and certifiable, nontransitional groups received a pre-emergent herbicide than the provincial average of 18% (Thomas et al., 1999), suggesting that this practice contributed to the achievement of PFP certification for some fields.
The proportion of fields receiving a postharvest tillage operation the year before PFP was not significantly different among groups (P = 0.08) (Table 7); however, the use of tillage among groups tended to increase as herbicide use decreased. The proportion of fields receiving a pre- or postharvest herbicide the year before PFP was significantly lower among certifiable, transitional fields than the other two groups. The proportion of noncertifiable and certifiable, nontransitional fields receiving a pre- or postharvest herbicide was similar to that reported for Manitoba (33%) (Thomas et al., 1999). Interestingly, 7% of certifiable, transitional fields also received a pre- or postharvest application of herbicide the fall before the initiation of the transition process.
A significantly lower proportion of certifiable, nontransitional fields received in-crop tillage than the other two groups (Table 7). Noncertifiable fields treated in this manner tended to be those on which farmers were experimenting with in-crop tillage and were subsequently sprayed because of poor weed control.
Fertilizer Use
There were significant differences in the proportion of fields that received synthetic fertilizer in the PFP crop year (P 
0.001) (Table 8). Not surprisingly, significantly fewer certifiable, transitional fields used fertilizer compared with both other groups. Virtually all Manitoba field crops receive synthetic fertilizer (Thomas et al., 1999). It is surprising, however, that fertilizer use was relatively low in the conventional groups compared with typical Manitoba levels. This may be indicative of the level of livestock production among participants, allowing for the use of leguminous forages or manure. It may also suggest that PFP is being attempted on relatively marginal land where all crop inputs are being reduced to decrease costs where yield potential is low. The lack of difference in fertilizer use between the two conventional groups gives no evidence to suggest that the use of fertilizer affected PFP certification.
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Row spacing. The use of narrow row spacing was not significantly different among groups (P = 0.12) (Table 8). The use of narrow row spacing may increase grain yields under weed competition (Kirkland, 1993). Increasing seeding rate may be a more effective way to increase crop density and competition (Roberts et al., 2001) and may be more easily modified than row spacing.
Seed source. The use of certified seed was not significantly different among groups (Table 8). In this study, there was no evidence to suggest that its use impacted the success of PFP certification.
Seeding date. Average seeding date as compared with same-year crop and regional average was not significantly different among groups, but fields in all groups were seeded between 6 and 8.1 d later than the same-year crop and regional average (Table 8). Delayed seeding was one of the most frequently mentioned strategies for PFP in all groups (data not shown). Delayed seeding can reduce weed pressure if early emerging weeds are eliminated before seeding (Spandl et al., 1999).
Treatment of Weed Patches
There were no significant differences in the proportion of fields with a subsection sprayed or mowed (Table 8). The attractiveness of mowing weed patches as a weed management practice is likely related to the availability of livestock on the farm to make use of such crops as feed.
Record-Keeping by Participants
For all groups, farmers kept near-complete rotation histories for less than 60% of fields (crop rotation known for at least 4 of the 5 yr previous to PFP) (Table 8). There were no significant differences among groups in this respect. Such records are important because crop rotation can reduce weed adaptation to the cropping system (Buhler, 2002). This lack of record-keeping is surprising because reduced-input farming can be supported by the input of farmers' knowledge of the cropping system (Van Acker et al., 2001; Bostrom and Fogelfors, 2002).
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SUMMARY |
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TOPABSTRACTINTRODUCTIONNOTESMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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The participatory approach used in this study was useful in assessing the implementation of PFP at the farm scale and was a valuable learning opportunity for the researchers involved. The observational nature of this type of study can be challenging because of the limited availability of baseline information for accurate contextual comparison. The successful execution of PFP by farmers in this pilot project suggests that there is good potential for farmers to explore PFP throughout Agroecoregion 2 of the NGP (Padbury et al., 2002). This region includes 3.6 million ha of cropland in Manitoba, Saskatchewan, and North and South Dakota. There is a need in the NGP for more dynamic, robust cropping systems that make use of both farmers' and researchers' expertise. Pesticide Free Production shows significant potential to provide a practical framework in which to implement these ideas on typical farms.
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ACKNOWLEDGMENTS |
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NOTES |
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