An experiment was started in 1991 to establish a crop rotation system where four single crop production components (ridge tillage; 3-crop wheat-corn-soybean; narrow (15′ wide), alternate strips; and legume interseeding) could be studied as an integrated farming system. The rotations (continuous corn, corn-soybean, wheat-corn-soybean where the wheat is interseeded with either Nitro alfalfa, vetch, or nothing) were set up in 1991 on a Webster clay loam (Typic Haplaquoll) on the Lynn Sorenson farm in Freeborn Co. In 1992, nitrogen rates of 0, 40, 80, and 120-lb/A were applied to corn following soybean, wheat, wheat + alfalfa, and wheat+ vetch to determine the N credit due to fixation by the legumes. Band applications of reduced rates of herbicide were applied to both corn and soybean. Mechanical weed control and ridge building were accomplished through cultivation. Yields and grain moisture of wheat, corn and soybean were taken in 1992 to evaluate the border vs. inside row effects of the strips, the interseeded legumes, and the response to N as effected by the cropping systems. Data on vetch and alfalfa yields, weed seedbank counts, root ratings and lodging to evaluate corn rootworm (CRW), tunnel counts to assess European corn borer (ECB) damage, and soybean cyst nematode (SCN) egg counts were taken. Yield data obtained in this second year, based on the assumption that the center two rows of a 6-row strip or the center 7 rows of the 21-row wheat strip represent a “whole-field” yield, showed: (1) 4% higher corn yields and 14% lower soybean yields compared to a “whole-field” average when grown in alternate strips and (2) 7% higher corn yields, 5% lower wheat yields, and 8% lower soybean yield when grown in the 3-crop strip rotation compared to a “whole-field.” Excessive spring re-growth of Nitro alfalfa and hairy vetch resulted in significant competition to the corn, resulting in stunted early growth, delayed maturity, and 20% lower corn yield compared to following wheat without a legume. Pest evaluation showed very little evidence of CRW or ECB activity. Soybean cyst nematode populations were considerably lower in the 3-crop system (no soybeans in 1991 or 1992) compared to those systems that included soybean in either 1991 or 1992. Weed counts indicated substantially more small grass and broadleaf weeds in corn following wheat in the 3-crop system compared to corn following soybean in the 2-crop rotation.
1) Determine the production and economic impact of wheat introduced into a conventional corn-soybean alternate strip rotation in a ridge tillage system.
2) Determine the potential of this 3-crop rotation to minimize insect, nematode, and weed pressures and thus reduce pesticide use.
3) Determine the effect of interseeding legumes with wheat on the potential fertilizer N savings, N availability to corn, and economics in a ridge tillage system.
4) Measure the border row vs. inside row effects of each crop on yield, pest incidence, N utilization, land utilization, and production economics.
5)Evaluate the ability of potential soil tests to predict available soil N for corn following soybeans and following wheat with and without interseeded legumes.
Obj. 1. —
Grandin wheat was planted directly into a previous crop of ridge-tilled soybeans on April 8, 1992 in 8-inch rows at a rate of 94 lb/A with a JD 515 minimum till drill. Seed:soil contact and seeding depth was satisfactory in the 30″ wide ridged soybean stubble. The wheat stand was excellent and the Nitro alfalfa stand was satisfactory. An additional 50 lb N/A was applied. Wheat alone and wheat+vetch plots were sprayed with Bronate (0.5 lb a.i/A) to control broadleaf weeds. Because there was no difference among the three wheat systems (wheat alone, wheat + alfalfa, and wheat + vetch) the yields were averaged. Wheat grain yields from the east one-third of the strip (bordering soybean) averaged 52.3 bu/A, while the center 1/3 of each strip averaged 54.4 bu/A. The west 1/3 bordering corn averaged 43.8 bu/A.
In the wheat alone strips, each individual row was hand-harvested to compare with combine-harvest yields and compare the ridge, shoulder, and valley rows. Grain yields from the hand-harvested sections closely matched the combine-harvest yields. Grain and straw yields from the shoulder and ridge rows were 23% higher compared to those of valley rows.
The following comments summarize our findings with wheat in this second year:
1) Wheat yields were affected by the position in the strip. Grain and straw yields from the east 1/3 of the strip (next to soybean) were reduced 4% and 10%, respectively, while grain and straw yields from the west 1/3 of the strip (next to corn) were reduced 20% and 17%, respectively, probably due to shading by the corn.
2) Wheat grain yields were not affected by the intercropped alfalfa. The vetch was not planted until mid-August, so wheat yields from wheat alone and wheat/vetch are not expected to be different.
3) Assuming a “field” average of 54.4 and a “strip” average of 50.2, we calculate the relative yield of 92 for the strips — or 8% lower than the whole field average.
4) Wheat straw yields of the strip system were 9% lower compared to the whole-field average.
5) Grain moisture at harvest was <1 point higher for the wheat from the east and west thirds of the strip compared to the center. Production economics for the first two years of data are to be calculated. Obj. 2. — European corn borer and Northern corn rootworm activities were almost nil and we did not observe any differences among the strip systems or within the strips with respect to corn root worm or European corn borer activity. Weed counts from the strips indicate substantially more small grass and broadleaf weeds following wheat in the 3-crop rotation compared to following soybean in the 2-crop rotation. Soybean cyst nematode populations were considerably lower in all cropping systems where either wheat or corn were grown in the last two years compared to those systems that included soybeans in either 1991 or 1992. Obj. 3. — Nitro alfalfa was seeded with the wheat at the rate of 12 lb/A. Hairy vetch (Madison cultivar) was seeded with the JD 515 drill on August 13 after wheat harvest. Stand counts and dry matter production were measured in October. Plant populations of both alfalfa and vetch were adequate, but the vetch yield was limited. Spring re-growth of Nitro alfalfa and hairy vetch was abundant. As a result, soil water in the seed zone was lower, seed germination and emergence were somewhat slower, and the re-growth provided too much competition for the small corn. The stunted corn never caught up in this cool year and maturity was delayed. Maximum grain yield of 131.4 bu/A was obtained for corn following alfalfa at 120 lb N/A rate, for corn following hairy vetch the maximum yield was 120.1 bu/A at 80 lb N/A rate. When corn followed wheat without interseeded legume, yields reached 155.6 bu/A with 120 lb N/A. In the spring of 1993, the alfalfa and hairy vetch re-growth was killed with a herbicide (Banvel) and top 2-3″ of the ridges were scalped to incorporate more of the vegetation before planting corn. Our 1993 data will enable us to determine the N credits from the two legumes and the potential for fertilizer N savings due to the N fixation. Obj. 4. — Corn (Pioneer 3751) was planted on May 11, 1992 at a rate of 30,200 plants/A in rows 2-5 and 36,000 ppA in the outside rows (1&6). Each corn strip following wheat and soybeans was sub-divided into four N rates (0, 40, 80, and 120 lb/A) to establish an N rate response curve. These treatments were compared to an N rate response curve using 8 N rates (0, 30, 60, 90, 120, 150, and 180 lb/A) for continuous corn. Insecticide was used only for continuous corn. Weeds were controlled with a 15″ band application of Lasso (3 lb ai/A) and Bladex (2.5 lb ai/A) on May 20, and ridge cultivation. Hand-harvest grain yields were obtained on October 23 from a 25-foot section within each row of each 6-row strip in each replication. Ears were removed from the 96 plots (448 individual rows), shelled, weighed and grain moisture was determined. The following comments summarize our findings with corn: 1) Corn grain yields in the outside rows bordering wheat on the east side (154.8 bu/A) and soybeans on the west side (148.3 bu/A) were 16% and 13% higher, respectively, than the average yield of the center two rows (129 bu/A) 2) Strip system corn yields following wheat were increased 7%-8% compared to the “whole-field” average (center two rows). 3) Yields from rows 2 and 5 (second from east and west, respectively) only yielded 6% and 2% higher than the center two rows. These data indicate that the yield advantage for the strip system is primarily due to the outside east row next to wheat and secondarily to the outside west row next to soybean. 4) Grain yield of the east outside row (next to wheat) appears to be consistently higher than the west outside row (next to soybeans). This is probably due to the wheat maturing earlier and not competing with corn, while the soybeans are still competing with corn for moisture, nutrients, and sunlight, etc. 5) An interaction between N rate and row position was not found. This indicates that N rate does not need to be adjusted within these alternate strips. Soybean (Sturdy) was planted on May 11 at a rate of 9 to 10 beans/foot in 30″ rows. Weeds were controlled with a pre-emergence, 15″ band application of Lasso (3 lb ai/A) on May 20, a post-emergence, 15″ band application of Pursuit (4 oz ai/A) on June 30, and by ridge cultivation. Each 120′ row of each 6-row strip was combine-harvested on October 15. Seed yield and moisture of each row were determined at that time. The following comments summarize our findings with soybeans: 1) Soybean yield was greatly influenced by row position in both corn-soybean and corn-soybean-wheat strips. Yield of the east row next to corn was only 71% of the center two rows, while the west row bordering wheat suffered only 6% yield loss. 2) The strip yield averages in both the 2- and 3-crop systems was consistently lower than the center two rows due to the reduced yield of the outside east and west rows. Obj. 5. In 1992, 0-3′ soil samples were taken in 1-foot increments from the 0-lb N treatments in all of the cropping systems. These samples were taken at three different times: a) pre-plant, b) emergence stage, and c) V5 (corn 8-12″ high) and were analyzed for soil NH4-N and NO3-N. The following comments summarize our findings with the soil tests: 1) Soil NH4-N prior to planting was not significantly different among the cropping systems. Soil NO3-N was highest following soybean, intermediate following wheat regardless of interseeded legume, and lowest in the continuous corn system. 2) Soil NH4-N concentration was higher in the 0-1′ layer and did not differ among the cropping systems at all (pre-plant, emergence, and V5) stages. 3) Soil NO3-N in the 3-foot profile at emergence stage was approximately 60% higher than at pre-plant stage. Greatest increase was noted in the 0-1′ layer and in the continuous corn, wheat, and wheat+vetch systems. This increase in NO3-N in the top layer indicates mineralization of organic N (either soil or legume biomass). 4) Soil NO3-N amounts in the 0-3′ layer at the V5 stage were similar to the emergence stage and were almost identical among the cropping systems. 5) It will be necessary to do this over a couple of growing seasons under different climatic conditions to evaluate the soil tests.
After only two years, it is difficult to project too far. However, based on these preliminary results it appears that:
1) Erosion could substantially be reduced because of high residue levels and no primary tillage with this 3-crop system.
2) Insect activity should be reduced by this cropping system, but early signs indicate that weeds may be more of a problem following wheat. This is especially true in the borders between the plots where cultivation misses some of the weeds. Total pesticide usage should be considerably lower than in most corn-soybean systems.
3) An excellent nesting habitat exists in the wheat for pheasants, which allows them to bring off one or maybe even two broods.
4) Finally, with this 3-crop narrow strip system, quality of surface waters should be enhanced markedly due to minimal runoff and erosion. It is too early to speculate how much affect this system will have on groundwater quality.
Economic analysis on the data collected so far will be completed in another couple of months. Agricultural economist on project did not return from sabbatical leave until July, 1993.
Educational & Outreach Activities
The following events were held:
Popular press: One article developed by THE FURROW magazine and interviews with other journalists.
Extension meetings: Three with a total attendance of about 550 to 600 people.
Field tours: Three plus another two at a companion site. Attendance was estimated at 475.
Videotape: One 10 minute tape
Conference: Presented a poster paper on the findings of this study at the Annual Agronomy Meetings (Nov. 7-11) held at Cincinnati, Ohio (copy of the abstract attached).
Areas needing additional study
After our experiences over the past two years, it has become evident that we need to give greater attention to the SCN and how it is impacted by these management systems. Also, there was some visual indication that dagger and sting nematode damage existed in some of the corn roots. This is unconfirmed yet at this time but needs further investigation.
The fixation of N by these legumes in these northern climates may need further investigation. Maximizing availability of the fixed N through improved management practices is necessary.
Lastly, reasons for the much lower soybean yield in the row next to corn need to be identified. Is it light (partial shading), CO2, moisture, root competition, etc? This appears to be a physiological affect and perhaps could occur in wheat as well. Additional years of the study will indicate the magnitude of the problem and its consistence from year to year.