The effects of shelterbelts on cropping and tillage practices

INTRODUCTION

By sheltering vulnerable land from wind, shelterbelts have been shown to reduce soil erosion, improve moisture conditions by trapping snow, and provide wildlife habitat. Furthermore, the improved microclimate caused by the combined benefits of moisture conservation and reduced wind erosion significantly increase crop yields (Kort, 1988).

This study was undertaken to determine whether shelterbelts affected the cropping and tillage choices made by producers. In particular, there were two main objectives:

1. to determine if producers who farm land protected by shelterbelts make different cropping choices than producers who farm unsheltered land, and;
2. to determine if producers who farm sheltered land differ from producers who farm unsheltered land in the type and amount of tillage practices, including the use of summerfallow and/or chemfallow.

It is important to understand how shelterbelts affect farming operations to ensure that shelterbelt programs and design recommendations are compatible with modern farming operations

The project was undertaken as a two-fold survey:

1. by field reconnaissance in 1997 of field sizes and crops on randomly-sampled quarter sections with or without shelterbelts,
2. by a follow-up survey mailed to randomly-selected producers farming with or without shelterbelts in the inspected rural municipalities.

The study focused on four Rural Municipalities(R.M.'s) (hereafter referred to by their specific RM names; "Auvergne" and "Fertile Valley" in Saskatchewan, and "Edward" and "Stanley" in Manitoba), where well-developed networks of mature shelterbelts are established. The RM of Fertile Valley is found in the Conquest area of central Saskatchewan, and the RM of Auvergne is located in the Ponteix area in southwest Saskatchewan. The RM's of Edward and Stanley are found in the southwest and south central areas of Manitoba near Lyleton and Winkler, respectively.

Methodology

Field survey

A field inventory was undertaken in the summer of 1997 in which a comparable number of sheltered and unsheltered quarter sections were inspected. The data recorded consisted of the number and size of fields and, for each field, the crop grown, and the number and size of fields in summerfallow.

Sheltered quarter sections were defined as those having at least 70% of the field area sheltered by rows of trees. Similarly, unsheltered quarter sections were those without shelterbelts, or with a land base in which 30% or less was protected by shelterbelts (i.e. a quarter section with a single shelterbelt was categorized as an unsheltered quarter).

Field sizes were determined by aerial photographs, and verified by visual inspections. Fields were categorized in nine, 20-acre increments.

A total of 228 and 287 quarter sections were inspected in Auvergne and Fertile Valley, respectively. A further 188 and 168 quarter sections were inspected in Stanley and Edward, respectively.

Producer survey

Questionnaires were mailed to producers in each RM. Quarter sections were chosen from aerial photographs and categorized as unsheltered or sheltered land, and landowners were subsequently identified from landowner maps. The primary criteria for landowners were that they:

1. farmed/owned more than one quarter section in the target RM,
2. farmed predominantly either sheltered land or unsheltered land.

The latter criterion was confirmed by questions in the survey.

Producers were asked to describe their tillage and cropping practices, as well as to rate environmental and market factors affecting their management decisions. Producers also provided specific details concerning field sizes, seeded crops and crop acreage for the years 1993-1997 inclusive (see Appendix III). The producer survey crop data was averaged over five years, giving an estimate of crop diversity and seeded acreage. In contrast, the field survey data provided a one season snapshot of farming practices and served as a comparison between long-term and short-term data. Responses were received from Fertile Valley (26), Auvergne (22), Stanley (9) and Edward (14).

BACKGROUND PHYSIOGRAPHY

Table 1 contains background physiography data about the four RM's studied. The sources are noted in the table.

Results

Field size

Areas with shelterbelts had, on average, smaller field sizes than areas without shelterbelts (Fig. 1a-d). In sheltered areas, fields of 80 acres or less comprised 96% and 93% of the total number of fields in the Saskatchewan and Manitoba RM's, respectively (Fig. 2b). However, the effect of shelterbelts of field sizes was greater in Manitoba where only 53% of the unsheltered fields were 80 acres or less (Fig. 2a) In the Saskatchewan RM's, 91% of the unsheltered fields were 80 acres or less (Fig. 2a). The small size of unsheltered fields in Saskatchewan was mainly due to strip-cropping, reflecting the greater risk perceived for wind erosion in Saskatchewan, especially in the RM of Auvergne. The lower risk of wind erosion in Manitoba and perhaps the greater ability to adopt reduced tillage technology or continuous cropping because of higher precipitation could explain the use of larger fields there in the absence of shelterbelts.

There was general agreement of the producer survey with the field survey although the producer responses represented fewer fields, thereby resulting in a greater degree of variability. In unsheltered fields, 100% and 67% of the fields were reported to be 80 acres or smaller for the Saskatchewan and Manitoba RM's, respectively (Fig. 2c). In sheltered fields, 98% of fields were reported to be 80 acres or less for both Manitoba and Saskatchewan (Fig. 2d).

These results were in agreement with the responses of producers to survey Question 17 (Table 2) in which 30% of all producers with shelterbelts said that their field size was affected by the shelterbelts, implying that, without the shelterbelts, the field sizes would likely be different. Particular comments to this question included the following:

• "... your field size can only be as big as your shelterbelts allow."
• "... because of shelterbelts, field size is small ..."
• "Field size was set many years ago when the trees were planted."
• "The field size will always be the same..."

These comments are further supported by the responses to Question 15 (Appendix I) in which shelterbelts were identified as one of the most important factors influencing field size.

Table 2. Responses of producers with shelterbelts about shelterbelt influences on cropping and tillage practices.

Crop diversity

The Manitoba RM's of Stanley and Edward had a greater diversity of crops than the Saskatchewan RM's while the least crop diversity was found in the Saskatchewan RM of Auvergne (Figure 3). This is likely due mainly to the differences in climatic conditions among the regions but other factors such as the availability of irrigation and the existence of local processors in Manitoba give producers the option to grow crops such as sugar beets and potatoes.

Table 3. List of crop abbreviations used in Figure 3.

A crop diversity index was developed (Equation 1) to determine whether a difference in the diversity of cropping choices could be discerned between unsheltered and sheltered fields (Table 4). The index took into account both the number of crops grown and the proportion of the total crop area occupied by each crop. A weighted average was also calculated which took into account the total number of acres of each crop over all four RM's. This was considered more useful than a simple average, especially for the producer survey, due to the difference in the number of responses from each RM.

The index was calculated as:

in which: Div = diversity index; crop = a particular crop; i = the number of crops; and p = the proportion of the total acreage (not including summerfallow acreage) in an area occupied by a particular crop.

Table 4. Crop diversity index (Equation 1) for sheltered and unsheltered areas

The crop diversity index appeared to be a good indicator of crop diversity because it accounted for both the number and acreage of crops grown. Because of the greater number of crops grown in the Manitoba RM's the index was greater than that for Auvergne. Because of the greater acreage of minor crops, the RM of Stanley, according the field survey, gave an average diversity index of 0.854 (sheltered and unsheltered) compared to 0.749 in Fertile Valley even though the number of crops grown were almost the same.

The weighted average crop diversity index for both the field and producer survey were slightly higher for sheltered areas than for unsheltered areas. In the field survey, the sheltered areas had a greater diversity index in three of the four RM's. In the producer survey, the sheltered areas had a greater diversity in only two of the RM's. Most of the producers who farm with shelterbelts felt that their shelterbelts influenced their crop choices allowing them to grow crops such as low-residue crops or wind-sensitive crops which they might not grow without the shelterbelts (Table 2). Particular comments to Question 17 (Table 2) included the following:

• "I have 2-rod strips of forage established on east side of shelterbelts."
• "... allows planting of low-residue crops."
• "Potatoes ... need good protection from the wind since they add little to the soil and harvest procedure leaves the land very susceptible to wind erosion."

Despite the variability of the data, the crop diversity index values combined with producer comments, led to the conclusion that the use of shelterbelts resulted in an increase in crop diversity.

Tillage practices

There was little difference in the amount of summerfallow between unsheltered and sheltered areas but there appeared to be an effect of shelter in the RM of Fertile Valley (Fig. 4).

In Fertile Valley, the field and producer surveys showed a range of 10.5% to 20.8% of the land in fallow (sum of percentage in summerfallow and chem fallow). Both surveys showed a greater percentage of fallow land in the unsheltered land than in the sheltered land, 20.8% (unsheltered) vs 15.7% (sheltered) in the field survey and 12.9% (unsheltered) vs 10.5% (sheltered) in the producer survey. This difference could be due to better moisture levels or higher crop yields in sheltered fields, and also coincides with an increase in crop diversity in sheltered fields in that RM.

Figure 4. Percent of total acreage in summerfallow and chemfallow as influenced by the presence or absence of shelterbelts - Field Survey and Producer Survey.

In Auvergne, there was no difference in the amount of summerfallow in unsheltered and sheltered areas (Fig.4). In this area, the need to use summerfallow as a low-input way to accumulate soil moisture and soil nitrogen and the reduced crop diversification options evidently influenced the decision to put the land in fallow more than any benefits of the shelterbelts.. The use of strip-cropping in the unsheltered areas or of shelterbelts allowed producers to use summerfallow at the same rates while protecting the soil from wind erosion.

There was no summerfallow in the RM of Stanley and only a little in Edward RM.

It appeared from Question 17 (Table 2), that some producers who had shelterbelts felt that the presence of the shelterbelts influenced the acreage of summerfallow but, with the exception of the RM of Fertile Valley, there was little difference apparent, either from the field survey or the producer survey.

In response to Question 17 (Table 2), most producers with shelterbelts did not feel that shelterbelts affected their tillage frequency. However, one comment was made that "with tree strips, I can work it an extra time and trees will slow down winds and help stop soil from blowing." It appeared, from the responses to Question 12 (Table 5) that there was a slightly higher frequency of cultivations in sheltered fields than in unsheltered fields. This could also be due to greater weed growth in the sheltered fields caused by higher soil moisture and higher temperatures.

Table 5. Frequency of cultivation (from producer survey Question # 12)

Discussion

Shelterbelts appeared to play a role in cropping and tillage practices but that role appeared to be different in each of the four RM's surveyed.

In the RM of Fertile Valley, sheltered and unsheltered fields did not differ in size, mainly because producers in the unsheltered areas limited the size of their fields, many by strip-cropping, due to a concern about wind erosion. In the questionnaire responses, 40% of producers on unsheltered land identified wind erosion as an important factor limiting crop yield (Appendix I Question 13c) while only 33% of producers on land protected by shelterbelts felt that wind erosion was an important limitation. In Fertile Valley, there was also a slightly greater diversification of crops in sheltered fields and a decrease in the area fallowed.

In the RM of Auvergne, both sheltered and unsheltered fields were small, as in Fertile Valley. In this case, the small size of the unsheltered fields was clearly due to the widespread adoption of strip-cropping as a protection against wind erosion (Appendix I Question 14a). As in Fertile Valley, more producers in the unsheltered area rated wind erosion as an important limitation to crop yields. Because cropping choices were less in this area, however, crop diversity was not greater on the sheltered fields than on the unsheltered fields. Producers identified soil moisture as being the second most important consideration (after crop prices) in their cropping decisions (Appendix I Question 5). The use of summerfallow did not differ between unsheltered and sheltered areas. It was concluded that, in this RM, climatic conditions were so dominant that shelterbelts had no effect on cropping and tillage practices.

In the RM's of Stanley and Edward, unsheltered fields were generally larger than fields with shelterbelts. This was recognized by producers (Appendix I Question 15g). Producers in both RM's cited wind erosion as an importantfactor limiting crop yields (Appendix ! Question 13c). This likely accounted for the fact that the producers in neither the unsheltered nor the sheltered areas fallowed their land. Producers in these RM's had many cropping choices available to them and there appeared to be slightly more crop diversification among producers in the sheltered areas, perhaps because of the small field size as well as the protection from the shelterbelts.

Shelterbelts affected one or more farm practices in all the RM's studied but it was apparent that, because of the many other factors to be considered by the producers, shelterbelt effects in cropping and tillage choices were generally small. The surveys showed, however, that many producers considered wind erosion to be an important factor limiting crop yields and tried to minimize it with measures such as shelterbelts, strip-cropping and continuous cropping.

References

• Eilers, R.G., L.A. Hopkins and R.E. Smith. 1978. Soils of the Boissevain-Melita Area, Manitoba Soil Survey Report No. 20. Manitoba Department of Agriculture.
• Ellis, J.G., D.F. Acton and H.C. Moss. 1968. The Soils of the Rosetown Map Area. Saskatchewan Institute of Pedology, University of Saskatchewan.
• Harland, M. 1997. Pers. Comm. Soil Conservation Technician, PFRA District Office, Morden, Manitoba.
• Kort, J. 1988. Benefits of Windbreaks to Field and Forage Crops. Agric. Ecosystems, Environ., 22/23:165-190.
• Saskatchewan Institute of Pedology, University of Saskatchewan. 1989. Preliminary Soil Map and Report, Municipality of Auvergne.
• Smith, R.E. and W. Michalyna. 1973. Soils of the Morden-Winkler Area, Manitoba Soil Survey Report No. 18. Manitoba Department of Agriculture.

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