D.A. Derksen, H.A., Loeppky, G.P. Lafond, and R.P. Zentner. Agriculture and Agri-Food Canada, Box IOOOA, RR# 3 Brandon, MB, R7A 5Y3; Box 760, Indian l lead, SK, SOG 2KO; 107 Science Place,

INTRODUCTION

Current trends in western Canadian agriculture include crop diversification, reduced tillage, and the efficient use of inputs. Little cropping systems research has been conducted to determine the impact of reducing herbicide and t'ertilizer inputs on weed communities crop yield, or production economics. The "Special Crop Management Study, (SCMS) was established to compare diversified and reduced-input crop rotations in zero-and conventional-tillage systems. This paper will summarize information on weed community dynamics, crop agronomy, and economic returns from the first four year cycle of this study.

MATERIALS AND METHODS

The study was located at the Indian Head Research Farm, Indian l lead, SK on a thin black rego chernozemic silty-clay soil. It began in 1990 with two Years of background research being conducted. 1999- 1995 represent the first cycle of the four year crop sequences used. The land had been in zero tillage since 1987 with the conventional-tillage area worked up in 199(:). The study had six crop rotations in each of zeroand conventional-tillage systems that followed a cereal-oilseed-cereal-lentil sequence (Table 1). All phases of the rotations were present each year with t'our replications. Crop seeding rates, tertilization~ and herbicide applications were done according to recommended practice. To simulate typical t'arm situations, legumes were seeded first (late April was targeted), wheat 7-10 class later t'ollowed bv oilseeds after another 710 days. In-crop herbicides used were the same in each tillage system. In the low-input rotations grassy weed herbicide usage was reduced by 50% (no treatment in wheat phases) and broadleaf weed control was reduced in teens of rates used or weed spectrum controlled. Delayed seeding by 10-14 days was practiced for the low-input wheat crops. Given that pulse crops occurred every other year in the second low-input rotation (R4), fertilizer rates were 5()Ô`, ol'those used in the high input rotations and seeding dates followed an early/late pattern every other year. Zero-tillage plots were seeded directly into standing stubble. Conventional-tillage plots were cultivated in the fall and spring using a field cultivator. Seeding was performed in troth tillage systems using a mod)fied Noble-Versatile hoe-drill that was equipped to band fertilizer between every other crop row. Fertilizer was applied with the seed or mid-row banded.

Weeds were counted by species just prior to the time of post-emergence herbicide application to determine the seedling communities, in late July to determine the mature plant or residual weed communities, and in the soil seed bank. Crops were harvested with a small plot combine, dried to a common moisture level, cleaned, weighed, and sent to the ('anada Grain Commission nor quality evaluation Nitrogen fixation was determined by the A-value method.

Data for the 1992-95 period, which represent the first cycle oi'the four-year crisp sequences, were used in the economic analysis. Economic returns were calculated based on product prices and input costs representative of the 1996 crop year. Net return was defined as the income remaining after paying for all cash costs plus machine overhead costs

RESULTS AND DISCUSSION

Total weed densities, averaged over four years, were lower in zero tillage at the seedling stage but were similar in late July (Tables 2, 3, and 4). In the fall of 1994 total weed densities in the soil seedbank were similar by tillage system. Reduced input rotations (R3 and R4) had similar or less weeds compared to the conventional input rotations (R1 and R2) with R4 having the lowest overall weed densities. The most diversified crop rotations (R5 and R6) had the greatest total weed densities.

Wheat yields following lentil were generally higher than following oilseed crops. Lentil yields were not significantly different between tillage systems. Pea yield was higher in zero tillage in one year.

Over all, zero tillage nitrogen fixation was 10% and 31% higher in lentil and pea crops respectively (Table S). Nitrogen fixation was greater for lentil grown in diversified crop rotations (RS and R6) in both tillage systems. but the effect was greater in conventional tillage.

Rotations that were managed using zero tillage practices earned the highest net return in 3 of the 4 years, and had the highest total net earnings over the four years of the study; however, the differences were not statistically significant in all situations (Table 6). Net returns from the zero tillage rotations averaged 1 1% higher than for the conventional tilled rotations. In the final three years of the study, the zero-till managed R4 had the highest net returns among all rotation/tillage systems.

CONCLUSIONS

Crop diversiftcation and reduced input production systems can be agronomically and economically feasible if integrated weed management strategies are employed. Varying seeding, dates, herbicide options, and crop competitiveness were important components for the success of this study.

Table 1.0. Crop rotations The rotations move from right to left (e.g.: in R5 spring wheat is grown after sunola).
	Phase in Rotation
Rotation	Cereal	Oilseed	Cereal	Pulse
R1: Post-Emergence Herbicides	Spring Wheat	Canola	Spring Wheat	Lentil
R2: Pre- & Post-Emergence'	Spring Wheat	Canola	Spring Wheat	lentil
Herbicides
R3: Low-Input Herbicides'	Spring Wheat	Canola	Spring Wheat	Lentil
R4 Low-input Herbicides & fertilizer	Spring Wheat	Pea(Pulse)	Spring Wheat	lentil
R5 Highly Diversified I	Canary seed	Sunola	Spring Wheat	Lentil
R6: Highly Diversified 11	Spring Wheat	Mustard	Canaryseed	Lentil
'Post-emergence herbicides used in the spring wheat phases and trifluralin used in canola and lentil In this rotation grassy weeds were not controlled in the spring wheat phases and reduced herbicide levels were used for broadleaf weed control Wheat seeding was delayed I ()-14 days compared to other rotations. J his rotation used the same herbicide approach as R3 and the rates of fertilizer used for all crops were half that applied in the other rotations (de: one half soil test recommendations)

Table 2. Average total densities #/m(2) (+ SE) of all weed species prior to in-crop spraying from 1992- 1995
	Rotation	Zero tillage	Conventional tillage
R1	wheat-canola-wheat-lentil	219+40	351+42
R2	wheat-canola-wheat-lentil	121+26	187+44
R3	wheat-canola-wheat-lentil	190+36	238+34
R4	wheat-pea-wheat-lentil	115+25	215+47
R5	canaryseed-sunola-wheat-lentil	84+11	202+30
R6	wheat-mustard-canaryseed-lentil	163+13	295+32
Contrasts
Zero vs Conventional tillage		0.03
Interaction of tillage system with rotation		<0.05
R1&R2 vs R3&R4		ns
R1 vs R2		<0.0001
R3 vs R4		<0.08
R1&R2 vs R5&R6		ns
R3&R4 vs R5&R6		ns

Table 3 Average total densities #/m(2) (+ SE) of all weed species in July from 1992- 1995.
	Rotation	Zero tillage	Conventional tillage
R1	wheat-canola-wheat-lentil	113+12	168+18
R2	wheat-canola-wheat-lentil	102+11	88+9
R3	wheat-canola-wheat-lentil	115+12	120+13
R4	wheat-pea-wheat-lentil	84+1-	74+7
R5	canaryseed-sunola-wheat-lentil	99+7	135+15
R6	wheat-mustard-canaryseed-lentil	141+12	172+18
Contrasts
Zero vs Conventional tillage		ns
Interaction of tillage system with rotation		ns
R1&R2 vs R3&R4		<0.003
R1 vs R2		<0.0001
R3 vs R4		<0.001
R1&R2 vs R5&R6		<0.1
R3&R4 vs R5&R6		<0.0001

Table 4. Average total densities #/m(2) (+ SE) of all weed species in the soil seed bank in the fall of 1994.
	Rotation	Zero tillage	Conventional tillage
R1	wheat-canola-wheat-lentil	4508+424	4467+430
R2	wheat-canola-wheat-lentil	4597+387	3965+251
R3	wheat-canola-wheat-lentil	4710+391	4778+499
R4	wheat-pea-wheat-lentil	3053+338	2951+302
R5	canaryseed-sunola-wheat-lentil	5377+1049	5505+885
R6	wheat-mustard-canaryseed-lentil	4890+723	4820+545
Contrasts
Zero vs Conventional tillage		ns
Interaction of tillage system with rotation		ns
R1&R2 vs R3&R4		<0.003
R1 vs R2		ns
R3 vs R4		<0.0001
R1&R2 vs R5&R6		<0.0001
R3&R4 vs R5&R6		<0.0001

Table 5. Average total densities #/m(2) (+ SE) of all weed species in the soil seed bank in the fall of 1994.
	Rotation	Zero tillage	Conventional tillage	Mean
R1	wheat-canola-wheat-lentil	68	47	58
R2	wheat-canola-wheat-lentil	63	50	57
R3	wheat-canola-wheat-lentil	65	52	59
R4	wheat-pea-wheat-lentil	72	62	67
R5	canaryseed-sunola-wheat-lentil	75	68	72
R6	wheat-mustard-canaryseed-lentil	72	70	71
		69	58	64

Table 6. Net Returns ($/ha) of Specialty Crop Rotations by Tillage Method and Year
Tillage	Rotation	1992	1993	1994	1995	Total
Conventional	R1: Post-emergence Herbicide	424	158	78	227	221
	R2: Pre-emergence Herbicide	465	150	119	261	249
	R3: Low-input Herbicides	434	195	187	188	251
	R4: Low-input Herbicides & Fertilizers	231	185	156	190	191
	R5: Highly Diversified I	492	131	24	132	195
	R6: Highly Diversified II	338	57	49	108	138
Mean		397	146	102	184	207
Zero	R1: Post-emergence Herbicide	505	174	70	191	235
	R2: Pre-emergence Herbicide	514	153	139	185	248
	R3: Low-input Herbicides	492	200	155	194	260
	R4: Low-input Herbicides & Fertilizers	309	246	195	234	246
	R5: Highly Diversified I	493	126	54	129	201
	R6: Highly Diversified II	475	79	86	124	191
Mean		465	163	117	176	230
Overall Mean		431	154	109	180	219

REFERENCES

Derksen, D A. R. E Blackshaw,. and S M. Boyetchko 1996 Sustainability, conservation tillage and weeds in Canada Can. J Plant Sci. ( in press)

Derksen. D A., A (, Thomas, G P Lafond. H N Loeppky. and C J Swanton 1995 Theimpactof herbicides on weed community diversity within conservation-tillage systems Weed Res. 35 3 I 1- 20

Derksen, D.A. A G Thomas. G. P Lafond, H A Loeppky. and J. Swanton 1994 The impact of' agronomic practices on weed communities fallow within tillage systems Weed Sci 42 184-194

Lafond, G P and D A Derksen 1996 Long-term potential of conservation tillage systems on the Canadian prairies Can J Plant Pathol 18 151-158

Lafond, G. P, D. A. Derksen, H. A. Loeppky, and D. Struthers 1994 An evaluation of conservation tillage and continuous cropping systems in east central Saskatcheuan J Soil and Water Cons 49 387-393

Lafond G. P., H. A. Loeppky and D A. Derksen 1992 The effects of tillage system and crop rotation on soil water conservation seedling establishment, and crop yield Can J Plant Sci 72 103-115