M. H. Entz and S.R. Smith

University of Manitoba, Winnipeg, MB

Email: Entz@agricbldg.Lanl.umanitoba.ca

Blaine G. Schatz

North Dakota State University, Carrington, ND

Email: Recenter@ndsuext.nodak.edu

1. IMPORTANCE OF CROP ROTATION

The importance of crop rotation has been recognized by farmers for centuries. Roman philosophers such Virgel, Cato and Varro described the beneficial effects of crop rotation compared with traditional fallow-based crop production systems. George Washington and Thomas Jefferson were also keenly interested in crop rotation; they exchanged ideas on the use of buckwheat and clover in early American cropping systems (Connor and Loomis 1993).

Today's farmers also recognize the importance of a diversified crop rotation. A survey of commercial fields in Manitoba revealed that field peas, flax, canola and barley all result in sizeable yield advantages to following wheat crops compared with wheat grown on wheat stubble (Bourgeois and Entz 1996). Research in western Manitoba (Hargrave et al. 1996) and Saskatchewan (Derksen et al. 1996) indicated that growing crops under no-till not only increased yield, but increased rotational yield benefits.

2. EXPANDING OUR DEFINITION OF CROP ROTATION

We typically think of crop rotation as growing different crops in a field in different years. However, there are other types of crop rotation schemes which are not usually considered in North American agriculture.

Relay Cropping involves seeding one crop before the first crop has been harvested. One advantage of relay cropping is that it makes better use of the time-temperature window. The time-temperature window is the amount of heat available to grow crops in a season (Cook and Veseth 1991). It is interesting to note that while wheat requires about 1200 growing degree days to complete its growth cycle, the period from April to October in Manitoba has about 1600 growing degree days. For example, in 1996 (a cool year), Melita MB received 1605 growing degree days between May 9 and Oct. 13. Since it took 1200 growing degree days to produce the wheat crop, 405 growing degree were "left-over". In many years, the amount of "left-over" growing degree days can be greater than 400; half of the required heat to grow a barley crop!

In semi-arid areas, there may not be enough soil water to make use of these additional growing degree days for plant growth. However in many parts of the Great Plains and Canadian prairie region, these additional 400 or so growing degree days are used to grow weeds. The question that we need to ask ourselves is whether we can use this additional heat to grow beneficial plants. Here are three examples of how we might make better use of the timetemperature window. Only example two is a true relay cropping system; the other examples are mod)fied relay cropping systems.

1. Seed a winter cereal immediately after harvesting a spring crop. In this way, the available heat and water in the fall period will be used to produce a crop and not weeds.
2. Seed clover (red clover or other) into a growing winter wheat crop in the spring of the year. After the winter wheat is harvested, the clover can be used as a late-season N fixer. This practice is used successfully in Ontario. A precision-farming wrinkle could be introduced here - only seed clover into the wetter low spots of the winter wheat field. In this way, you can "grow nitrogen" in those areas of the field with aufficient water to support fall growth.
3. Another mod)fication of the relay crop system is to seed a drought tolerant green manure crop immediately after winter cereal harvest. Trials in Manitoba showed above ground dry matter production after 48 days of growth was 1000 lb/acre for Chickling vetch (AC Greenfix), 980 lb/acre for Indian Head lentil, 720 lb/acre for Hairy vetch, 660 lb/acre for Berseem clover, and 1230 lb/acre for Nitro alfalfa. Percent ground cover (a measure of weed competition ability) was 77%, 80%, 73%, 53%, and 72% for these crops, respectively.

Intercropping means growing two crops together in the same field. Many farmers remember the days when oat/barley or oat/wheat intercrops were used as feed crops. Other examples of intercrops which have shown promise are flax/lentil (flax helps keep lentils off the ground, thereby improving lentil quality), pea/mustard, pea/barley.

3. ADDING "NEW" CROPS TO THE ROTATION

The performance of traditional crops such as wheat, barley, flax, canola, peas, lentils in no-till systems has been documented. However, less attention has been focussed on alternative crops in soil conserving cropping systems. One objective of this paper is to summarize current knowledge on different "alternative" crops, and to give an opinion on their suitability to no-till production systems.

Forages

While forages are not new to prairie agriculture, the experience of no-till forages is limited. Research has shown that benefits of forages such as alfalfa or alfalfa/grass mixtures are usually as great or greater under no-till than tilled systems (Entz, unpublished data). A summary of rotational benefits of alfalfa is given in Table 1.

Table 1. Influence of alfalfa on a number of different agronomic and environmental parameters
Parameter	Nature of Alfalfa Influence	References
Soil nitrogen	Five year alfalfa stand provides significant N for two following crops. N benefit can last up to 7 years Release of N from legume residue slower when legume stand terminated using no-till Annual alfalfa crops can contribute an average 50 kg had N to the soil. As high as 120 kg/ha	Ferguson and Gorby (1971), Bowren and Cooke (1975), Hoyt and Leitch (1983), Badaruddin Meyer (1990), Mohr, Entz and Janzen (unpublished data) Bruuslema and Christie (1987), (1994).
Soil structure	Alfalfa roots perform "biological tillage", thereby improving soil environment for root growth of subsequent crops. On heavy clay soils, inclusion of alfalfa in rotation increases soil water infiltration. No- till alfalfa removal keeps pores intact. "Systems that rely less heavily on tillage to increase infiltration of water into soil stand the greatest chance for long-term success" (West et al. 1991. Soil Sci. Soc. Am. J. 55:460-466).	Blackwell et al. (1990), Entz (1994) Cavers and Eilers, Dept. of Soil Sci, IJ of MB (1994)
Subsoil N	A four year alfalfa stand effectively extracted N to a depth of 260 cm on an Osbourne clay soil in Manitoba. Fallowing the year afler afler forage breaking increases subsoil N, thereby increasing the risk of groundwater contamination.	Entz and Vessey (unpublished) Campbell et al. (1994)
Weeds	T wo or three years of forage in a six year rotation virtually eliminated wild oat in cereal crops. A survey of commercial fields in Manitoba indicated sign)ficantly fewer wild oat, green foxtail and Canada thistle plants in wheat following forage crops vs. wheat following annual crops. Eighty percent of producers in a MB/SK survey indicated fewer weeds in annual crops after forage-breaking compared with annual crops in an annual crop rotation. (rood control of wild oat, green foxtail and Canada thistle was observed for a period of one (11 % of respondents), two (50% of respondents), or more (33% of respondents) years	Secmens (1963) Ominski ct al. (1994) Entz ct al. (1995)
Soil water status after alfalfa	Black and Gray soil zones: Soil water in 0 to 60 cm usually recharged in alfalfa rotation, but subsoil drier. Fallow not required for water recharge afler forage-breaking. Removing alfalfa stands using no-till increases soil water recharge by up to 3 cm. Dark Brown soil zone: Including alfalfa in rotation results in moisture shortages in following year. Fallow required for water recharge afler forage-breaking. (1994),	Hoyt and Witch (1983), Entz Bullied and Entz (1994) Brandt and Keys (1982)
Green house gases	Adding alfalfa reduces carbon emissions associated with crop inputs - nitrogen fertilizer machinery costs and fuel. C emissions over 10 years were 1611 kg/ha in a straight grain rotation vs. 941 kg/ha where a 3 year alfalfa was included in the grain rotation	Coxworth, Entz, Henry, Bamford Schoofs, Ominski and Leduc (1995).
Grain yield of following crops	Recent survey indicated that 71% of producers in MB and SK observe a yield benefit from including forages in their crop rotations. Yield benefit greatest in wetter areas and lowest in Brown soil zone. Yield benefits decrease sharply as alfalfa stand length increases beyond four years. Cumulative yield benefit occurs when legumes repeatedly included in cereal-based crop rotation. In dry years, grain yields greater when alfalfa removed using no-till vs. tilled system.	Entz et al. (1995) Poyser et al (1957) Entz and Gulden (unpulished data)

ANNUAL CROPS

The performance of various alternative annual crops are being investigated in a number of locations in the Great Plains and Canadian prairie region. These include Brandon, MB (Jack Moes, MB Agriculture - summarized in Moes, 1996), Swift Current, SK (Perry Miller, Agriculture Canada), Manitoba Crop Diversification Centre (Scott Wright, Carberry, MB) and the NDSU station at Carrington (Brain Schatz). The following table describes the observations made by Schatz and coworkers at the CarringtonResearch Extension Centre in central North Dakota. The averages or ranges listed in the table reflect on 9 years of performance testing for most crops. Also, these data describe the trial means within a year and not the range of cultivars within a trial.

Crop	Days to maturity	Seed rate (PLS or lb/acre)	Seed yield (lb/acre)	Cool vs. warm season type	Post-E herbicide selection	Suitability to no-till
Pea	93 (88-97)	300,000 PLS	2920 (1381-4153	Cool	Good	Excellent
Lentil	94 (82-99)	500,000 PLS	954 (50-2112)	Cool	Fair	Excellent
Fababean	110 (98-131)	180,000PLS	2237(928-3407)	Cool	Fair	Excellent
I.upin	110 (105-117)	250,000 PLS	1667 (852-2394)	Cool	Fair	Very good in other production areas
Chickpea	112 (101 - 122)	140,000 PLS	947 (48- 1958)	Cool	Fair	Very good in W. Canadian trials
Dry bean	114 (93- 101)	70 -90,000 PLS	1845 (552-3475)	Warm	Good	Very good in W. Canadian trials
Soybean	113 (99-127)	160,000 PLS	1641 (990-2376)	Warm	Very good	Ontario: Poor in cold, wet springs
Crambe	90 (84-102)	20lbs	1581 (918-2198	Cool	Fair	No information
Canola	94 (85- 101	17 PLS per sq. foot	1370 (212-2521)	Cool	Fair to excellent	Good
Mustard	90 (83-99)	17 Pl.S per sq. foot	1249 (510-2200)	Cool	Fair	Good
Sunflower	122 (121-122)	24,000 PLS	2102 (1647-3426)	Warm	F air	Good.Deepest rooting annual crop
Buckwheat	--	40-50	966 (167-1689)	Warm	Poor	No information
Triticale	--	1 million PLS	2508 (915-3460)	Cool	Fair	Good
Proso Millet	87	25	2127 (588-3455)	Warm	Fair	No information
Canary Seed	--	30	883 (655-1111)	Cool	Poor	No information

REFERENCES

Badaruddin, M., and D. W. Meyer. 1990. Forage legume effects on soil nitrogen and grain yield, and nitrogen nutrition of wheat. Crop Sci. 30: 819-825

Blackwell,P.S., T.W. Green, and W.K. Mason. 1990. Responses of biopore channels from roots to compression by vertical stresses. Soil Sci. Soc. Am. J. 54:1088-1091.

Bourgeois, L. And M.H. Entz. 1996. Influence of previous crop type on yield of spring wheat: Analysis of commercial field data. Can.J. Plant Sci. 76:457-459.

Bowren, K.E. and D.A. Cooke. 1975. Effects of legumes in cropping systems in northeastern Saskatchewan. Can. l. Plant Sci. 55:351.

Brandt, S.A. and C.H. Keys. 1982. Effect of crop rotations on soil moisture levels. p. 38-48. In: Proc. Soils and Crops Workshop, University of Saskatchewan, Saskatoon, S7N OWO.

Bruulsema, T.W. and B.R. Christie. 1987. Nitrogen contribution to succeeding corn from alfalfa and red clover. Agron. J. 79:96-100.

Bullied, W.J. and M.H. Entz. 1994. Using herbicides instead oftillage to remove forage stands. p. 177-183. In: Proc. Manitoba AgriForum. 16 Lowell Pl., Winnipeg, MB, R3T 4H8.

Campbell, C.A., G.P. Lafond, R.P. Zentner, and Y.W. Jame. 1994. Nitrate leaching in a Udic Haploboroll a s influenced by fertilization and legumes. J. Environ. Qual. 23:195-201.

Cook, R.J. and R.J. Veseth. 1991. Wheat health management. American Phytopath. Soc. 3340 Pilot Knob Rd., St. Paul, MN, 55121.

Coxworth, E. et al. 1995. Studies ofthe effects of cropping and tillage systems on the carbon dioxide release by manufactured inputs to western Canadian agriculture. Report to Agric. and Agrifood Canada, Lethbridge Research Station.

Loomis, R.S. and D.J. Conor. 1992. Crop Ecology. Cambridge University Press.

Entz, M.H. 1994. The role of forages in prairie crop rotations: 1994 annual progress report. Dept. of Plant Science, Univ. of Manitoba, Winnipeg, MB, R3T 2N2. 45 pp.

Entz, M.H., W.J. Bullied, and F. Katepwa-Mupondwa. 1995. Rotational benefits of forage crops in Canadian prairie cropping systems. J. Prod. Agric. 8:521-529.

Derksen, D.A., H.A. Loeppky, G.P. Lafond and R.P. Zentner. 1996. Reduced fertilizer and herbicide usage with pulse crops in rotation. P. 2223. In Proc. Pulse Crops Research Workshop, Calgary, AB, Nov. 1996.

Ferguson, W.S. and B.J. Gorby. 1971. Effect of various periods of seed-down to alfalfa and bromegrass on soil nitrogen. Can. J. Soil Sci. 51 :65-73.

Hargrave, A.P., D.R.S. Rourke, H. Xie and S. Gorrie. 1996. Conservation tillage productivity centre report. p. 47-53. In Proc. Of 18 annual Manitoba-North Dakota zero-tillage farmers workshop.

Hoyt, P.B. and R.IJ. Leitch. 1983. Effects of forage legume species on soil moisture, nitrogen and yield of succeeding barley crops. Can. J. Soil Sci. 63:125-136.

Kelner, D.1. 1994. Short-term alfalfa stands in cropping systems: genefits related to nitrogen. MSc. Thesis, Dept. of Plant Science, University of Manitoba, R3T 2N2.

Moes, J. 1996. Alternative crops under zero-tillage. P. 179-180 In: Proc. Manitoba/ND zero-tillage farmers association workshp, Jan., 1996, Minot, ND.

Ominski, P D.' M.ll. Entz7 and M. (Goodwin 1994. Using alfalfa to control weeds: A comparative study. P 17U-176. In: I'roc. Manitoba AgriForum, 16 I.owcil Pl., Winnipeg. MH, R31'4H8.

Poyser, E.A., R.A. Hedlin, A.O. Ridley. 1957. The ettect of farm and green manure on the fertility of blackearth-meadow clay soils. Can J. Soil Sci. 37:4g-56.

Siemens, L.B. 1963. Cropping systems: An evaluative review ofthe literature. Dept. of Plant Science, Univ. of Manitoba, Wpg., R3T 2N2. 89pp.