INTERCROPPING LEGUMES IN SUNFLOWER TO INCREASE SURFACE RESIDUE

Herman J. Kandel and Albert A. Schneiter

Crop and Weed Sciences Department,

North Dakota State University,

Fargo, ND 58105

Spring sown wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) have been grown in North Dakota since the prairies were brought under cultivation about a hundred years ago. The first commercial production of oilseed sunflower (Helianthus annuus L.) in the United States, occurred about 1966. Sunflower has since become an important crop especially in areas where moisture limits crop production. By 1979, 3.5 million acres of sunflower were grown in North Dakota (McMullen, 1985). Sunflower stubble is ineffective for snow trap because of its limited surface cover (Unger et al., 1988). There has been an increased awareness among agronomists and producers of the value of protecting soil from wind and water erosion. Legumes which can both increase soil fertility and reduce soil erosion have become increasingly important in farming systems. Limited information about farming operation involving inteerseeding legumes in sunflower have previously been reported (Anderson, 1991, Lilleboe, 1991 and Hulse, 1993).

Intercropping is not a new concept as it is a common practice in tropical countries. A good intercropping combination should increase total production per unit area as compared to a pure crop. Several researchers have reported on studies intercropping sunflower with legumes. Putnam (1986) reported that sunflower is a crop well adapted to intercropping. Zekeng (1980) studied strip-intercropping soybean (Glycine max(L.)Merr.) and dry edible bean (Phaseolus vulgaris L.) in sunflower at Fargo, North Dakota. She reported intercropping did not significantly influence the yield of the sunflower but reduced yields of both soybean and edible beans.

Leach (1986) evaluated a legume (Vigna trilobata L. Verdc.), for its potential to provide ground cover under sunflower , in an Australian subtropical environment. He concluded that although there were yield reduction in sunflower, the additional long term financial benefits of the legume in the system outweighed sunflower losses.

Legumes in a cropping system have the potential for adding biologically fixed nitogen to the system. Power and Doran (1988) reported that legume cover crops reduced fertilizer N requirements for the next grain crop by 45 to 107 lb acre –1. Mineralized nitrogen, from the legume biomass, provided the following grain crop with a slow-release source of nitrogen. In addition, cover crops protect against soil erosion (Power and Doran, 1988) and improve winter snow trap (Unger et al., 1988).

When legumes are interested in a commercial crop, too early in the season, they may render undersigned competition with the main crop (Gilley et al., 1989).

Gardner (1992) reported that at Carrington, yellow-flowered sweetclover (Melilotus officinalis Lam.), hairy vetch (Vicia villosa Roth.), foxtail dalea (Dalea alopecuroides L.), and black lentil (Lens esculenta L.) were the most promising of 42 legumes tested for use as a cover crop.

Yellow flowered sweetclover is more drought tolerant and easier to establish than white flowered sweetclover (Melilotus alba Medik.). It has been grown in North Dakota since the beginning of the century and is well adapted (Helm and Meyer, 1993). Meyer, (1987) reported it has potential as an alternative to fallow.

In 1992, a farm survey was conducted among 16 North Dakota producers who interseed legumes in their sunflower. The objective of the survey was to obtain information about methods of crop management, production problems and effects of legumes interseeded in sunflower. Data from the producers indicated they interseeded a total of 1,159 acres of sunflower with a legume. This was equal to 29% of their sunflower production. Average farm size was 1,520 acres with an average of 269 acres sunflower. The producers reported they interseeded legumes in both oil and nonoilseed sunflower. The majority of producers (15) grew sweetclover, but black medic (Medicago lupulina L.)(2), hairy vetch (1), Australian medics (Medicago sp.)(1) and fenugreek (Trigonella foenum graecum L.)(1) also were grown. The producers, used an average of 9 lb of sweetclover sown with an average sunflower population of 18,000 plants acre –1. Producers reported their legumes were sown at different times. Two of the producers reported their legumes were sown on the same date as their sunflower. Eight, five and one of the producers reported the legume was sown at first, second and third sunflower cultivation respectively. The majority of the producers (15) broadcast their legume seed in front of the cultivator. One producer broadcast his legume seed without incorporation. Two producers attempted aerial broadcasting without cultivation.

The majority expressed interest because of the potential of legumes to fix nitrogen. Two producers reported harvesting sweetclover as hay, the year folowing sunflower. Ten growers tilled the legume in the spring versus nine in the summer, in which case the legume had an opportunity to develop and fix more nitrogen. Seven producers who tilled the legume in spring, subsequently grew wheat and barley. Other producers did not plant a crop the year following sunflower. Gardener et al. (1991) reported that a good stand of sweetclover can add more then 75b lb of N acre –1 by early June, after which the legume was tilled to preserve moisture. This left the soil unprotected against erosion forces.

The major problems reported by producers associated with interseeding legumes in sunflower are presented. The cost of sweetclover seed in 1991 was estimated at $0.32 lb –1 (Anderson, 1991). At an average seeding rate of 9 lb acre –1 sweetclover, seed would cost $2.88 acre –1 compared with an estimated $20.80 acre –1 for hairy vetch (Gardener at al., 1991). Producers generally sowed the legumes in the sunflower as the canopy was closing and the temperatures were high. Because of this, successful stand established was dependent on timely rains.

Fourteen of the producers indicated that they would recommend interseeding of legumes in sunflower to their neighbors. Only two producers felt that the system was not beneficial.

Although a number of North Dakota sunflower producers are experimenting with interseeding legumes, no previous research had been conducted to establish the benefits or lack of benefits of interseeding legumes in sunflower. One of the objectives of our research is to evaluate which five selected legumes is best adapted to North Dakota farming systems.

Some producers may decide to grow small grain crops after sunflower/legume combination in which case the effects on grain yield and protein content are of importance. Other producers want to establish a legume in a sunflower field, intended for green fallowing after the sunflower crop.

1. Determine the response of sunflower to legume interseeding.
2. Determine the most suitable, from five selected legumes, for interseeding in sunflower.
3. Determine opportune planting date for the legume.

The duration of this research project will be three years, with field experiments at Prosper and Carrington, ND.

The soil at Carrington is a Heimdal loam which is a coarse-loamy, mixed Udic Heploborolls. The soil at Prosper, which is located 16 miles NW of Fargo, is a Bearden silty clay loam which is a fine-slay, frigid Aeric Calciaquolls.

Weather information, including temperature and rainfall is obtained from field weather stations. Fertilizer was applied for a sunflower yield goal of 2500 lb acre –1 (Dahnke at al., 1990).

The herbicide Treflan1 was applied prior to sunflower seeding. Sunflower heads were harvested after physiological maturity, dried in a forced air dryer, and threshed with a combine. Samples were cleaned and weighed.

Data from all studies are being analyzed using the Statistical Analysis System (SAS Institute, 1982). If error variances of individual environments are homogeneous, the experimental data are combined over environments. Environment is considered a random effect. All other effects are considered to be fixed. The Least Significant Difference (LSD) were calculated according to Carmer et al. (1989) and Gomez (1984).

The experimental design was a split-split plot arrangement in a randomized, complete block, with four replicates. Studies were conducted at two locations, Prosper and Carrington, North Dakota, for two growing seasons (1992 and 1993). The plot size was 20x10 feet (1992) and 25x10 feet (1993) with four rows of sunflower, 30 inches apart. Legume seed was broadcasted between the sunflower rows. The main plot consisted of two sunflower hybrids; ‘Interstate 331’ with conventional height and maturity and the earlier maturing dwarf ‘Sunwheat 101,’ grown with an average of 23,900 plants acre –1. Legume sowing dates constituted the sub-plot. Legume planting dates were the same as sunflower (PLT), approximately 30 days after the sunflower (four leaf stage, V4), and approximately 49 days after sunflower (ten leaf stage, V10). The sub-sub plot consisted of five different legumes sown and one plot without a legume as a control plot. All legume seed was inoculated, just before sowing, with legume specific rhizobia bacteria.

Sunflower yield was established from 10 feet of the two center rows. After the first killing frost, a legume biomass sample was taken from 1.2 yard2 plot between the sunflower rows.

Light reaching the soil surface under the sunflower canopy, was determined in the control plots with a Li-cor L1188₁ integrating photometer.

Data collected or calculated included:

1. Growing degree days for sunflower,
2. Sunflower achene yield,
3. Sunflower plant height,
4. Legume biomass,
5. Canopy light penetration.

From the five legumes included in the trial only alfalfa and sweetclover survive the winter conditions in North Dakota.

Carrington received 6.38 inches of rain while Prosper received 14.52 inches. Because of this sunflower yields at Carrington averaged 919 lb acres –1 less than at Prosper. At Carrington, moisture limited the growth of the legumes. The third legume sowing date at Carrington was under drought stress. Germination of alfalfa and sweetclover was poor and no significant ground cover was obtained. Due to the favorable moisture condition at Prosper, the legumes sown with sunflower were able to produce good cover. Growth of hairy vetch was so abundant that the legume crawled up the sunflower stalks and in fact suppressed yield of the dwarf hybrid. At Prosper, the legumes grew better in the short statured hybrid than in the tall hybrid, probably because of increased light penetration.

Carrington received more than three times the amount (19.49 inches) of rainfall as compared with 1992. Prosper received 18.08 inches. The abundant rainfall and low temperatures in the beginning of the growing season were favorable for the development of the legumes. No moisture stress was experienced during the season. The legumes sown together with the sunflower were very competitive. Sunflower weevils (Smicronyx sordidus Le Conte) reduced sunflower yields at Carrington.

The combined data for Prosper and Carrington in 1992 and 1993, indicated significant yield differences between hybrids. ‘Interstate 3311’ produced 1,540 and "Sunwheat 101’ 1,309 lb acre –1. The sunflower yields were significantly lower 1,261 lb acre –1 (P<0.05) when the legumes were sown direct with the sunflower compared with the yields of 1,502 and 1,510 lb acre –1 when legumes where sown at the four and ten leaf stage of the sunflower development, respectively.

Only black lentil did not reduce the yield significantly (P<0.05) when sown directly with the sunflower. Legumes planted at the four leaf or ten leaf stage of sunflower did not reduce the sunflower yields.

The biomass data are combined for Prosper and Carrington 1992. As expected the legume biomass was highest when the legume was sown the same time as sunflower. Sowing the legume 30 days after the sunflower (V4) greatly reduced legume biomass production. Sowing of the sweetclover 49 days after the sunflower (V10) produced 149 and 19 lb biomass acre –1 at Prosper and Carrington, respectively. This is not enough to have a good soil cover and also the chance of winter kill is substantial. Sweetclover and alfalfa sown at V4 had good soil cover and strong plants, able to survive the winter. Some hairy vetch survived the winter also. Hairy vetch had the highest biomass production.

The legumes intercropped with the sunflower were allowed to grow until the first killing frost. Legumes sown at the four leaf stage of sunflower development, on average, had a 119 day growing period.

Incoming solar radiation was measured on clear days. As the canopy closed less light reached the soil. A greater amount of light reached the soil surface with the dwarf hybrid than with in the conventional hybrid. If legumes are planted later in the season (V10) the canopy is closing and the growth of the legumes is slower. As has been abundant growth of the legume when planted the same time as the sunflower reduces the sunflower yields. Planting at the sunflower V4 stage gave an adequate soil cover, and plants are most likely able to survive the winter. Broadcasting of the legumes could take place at first cultivation, around the V4 stage. Observations in the 1993 season indicate that the legumes sown at the V4 stage developed well and did not reduce yield of sunflower. A mixture a hairy vetch and sweetclover was sown in some observational plots. This combination would increase the chance of having a soilcover going into the winter as the vetch is able to establish itself better, partly due to the bigger seed.

1. Legumes performed better in the shorter sunflower hybrid ‘Sunwheat 101’ than in the conventional height hybrid ‘interstate 3311’.
2. A greater amount of light reached the surface in ‘Sunwheat 101’ compared with ‘Interstate 3311’.
3. Sowing legumes at the same time as the sunflower produced the greatest legume biomass.
4. Sowing the legumes at the last cultivation (44 and 49 days after sunflower in Prosper and Carrington respectively) did not produce sufficient biomass to cover the soil in 1992.
5. Sunflower yields were sufficiently reduced by interseeding legumes at the same time as planting the sunflower, except by using black lentil.
6. Sunflower yields, with legumes sown at the four or ten stage, were not reduced.
7. Hairy vetch is an aggressive grower and produced the overall highest amount of biomass. Present seed costs may limit it’s acceptability by producers. A mixture of sweetclover and hairy vetch may reduce the seed cost. It is not recommended to sow the hairy vetch together with the surface until after the four leaf stage. Hairy vetch gives a good soil cover going into the winter, most plants do not survive the winter. A grain crop can be drilled into the remaining of the crop in the spring.
8. Some producers interseed sweetclover in their sunflower, to establish the sweetclover as a green manure crop the year after sunflower. The cost of sowing is minimal because the seed is cheap and sowing can be done during cultivation. Expected benefits are soil protection, fixation of nitrogen and addition of organic matter to the soil.
9. Sweetclover needs to be killed properly before a small grain crop is sown the spring after the sunflower/sweetclover intercrop. If this is not done sweetclover acts as a weed and will reduce small grain yield.
10. Black lentil may be sown together with the sunflower. The crop provides sufficient soilcover going into the winter but does not survive. A following grain crop can be drilled into the stubble.

NDSU Extension service: Dr. Duane Bergland, the staff of Carrington Research Station, statistician: Dr. Richard Horsley, technician: Dr. Burton L. Johnson.

¹Mention of trade names, proprietary products, or vendors does not constitute a guarantee or warranty for the product by North Dakota University, and does not imply its approval tot the exclusion of other products or venders that may be suitable.

Anderson, L. 1991. Interseeding sweetclover in row crops promising. Farm and Ranch Guide, March 22, 1991.