Integrating Perennial Living Mulches into Irrigated Cropping Systems

Integrating Perennial Living Mulches into Irrigated Cropping Systems

Summary

Results from the first year of this study indicate that it is possible to establish various perennial legumes for use as living mulches by employing conventional cover crop practices or co-establishing them with corn. This is important since it takes some of these legumes a year to fully establish. Producers would be reluctant to adopt such a system if they had to take land out of production for a year. Suppressing the living mulch without killing it appears to be the main problem associated with the system that must be worked out before producers are willing to consider implementing it.

Objectives/Performance Targets

1. Determine methods of establishing various perennial plant species potentially adapted for use as living mulches under irrigation.

2. Evaluate methods of suppressing living mulches to avoid reduced yields of associated crops.

3. Quantify the environmental and economic benefits of using living mulch systems under irrigation.

4. Demonstrate the benefits of using living mulch systems for crop production under irrigation to producers through on-farm trials.

Accomplishments/Milestones

The following legumes, white clover, birdsfoot trefoil, and a mix of red, white, and kura clovers, were successfully established as perennial living mulches at 2 sites near Fort Collins, Colorado. One site was irrigated with a linear drive sprinkler and the other by flood irrigation using gated pipe. The legumes were seeded with a cover crop of either oats or corn. At the sprinkler irrigated site, there were two complete sets of oat plots which were both harvested as hay, one at the boot stage and the other at soft dough. The corn was harvested as silage at the half milk line stage. At the flood irrigated site, the oats were harvested once for hay at the soft dough stage and the corn for silage at the half milk line stage. There was also a set of plots in which the legumes were planted into a clean-tilled seedbed. Due to herbicide carryover issues, the legumes only established in the oat plots at the flood irrigated site. The degree of legume establishment will be evaluated at both sites in the spring of 2010 prior to any suppression treatments being implemented. This timing of sampling takes into account any potential winterkill issues and normalizes any differences in legume growth due to differences in harvest dates between the oat and corn plots in 2009. The yield and quality of the oat and corn silage cover crops were determined. This data will be used later in an economic analysis of perennial living mulch cropping systems.

At the Fruita, Colorado, location, previously established plots of the following legumes, alfalfa, birdsfoot trefoil, red clover, white clover, and a mix of birdsfoot trefoil and red clover, were suppressed using a combination of strip tillage and herbicides (glyphosate and paraquat) prior to seeding corn for silage, corn for grain, and soybeans for grain. The herbicide rates were apparently too high for most of the legume species and instead of suppression, all but the birdsfoot trefoil was killed. In the corn grain and silage plots, there were also plots without legumes to which we applied fertilizer at rates of 0, 84, 168, and 252 kg/ha of nitrogen. This allowed us to develop a nitrogen response curve to determine inputs from the legumes associated with atmospheric nitrogen fixation. All legume plots received 84 kg/ha of nitrogen fertilizer plus whatever was provided by the legume.

The added nitrogen benefit from the various legumes in the corn silage plots averaged 54, 35, 25, 36, and 17 kg/ha for the alfalfa, birdsfoot trefoil, red clover, white clover, and mix of birdsfoot trefoil and red clover, respectively. In the corn grain plots, the nitrogen contribution from alfalfa, birdsfoot trefoil, red clover, white clover, and mix of birdsfoot trefoil and red clover averaged 46, 23, 21, 55, and 26 kg/ha, respectively. Corn silage yields ranged from 17.2 Mg/ha in the birdsfoot trefoil plus red clover plots to 20.4 Mg/ha in the alfalfa plots while corn grain yields ranged from 8.2 Mg/ha in the red clover plots to 10.1 Mg/ha in the white clover plots. There were no differences in soybean yields (avg. 3120 kg/ha) associated with legume living mulch species which is not unexpected since all are legumes. In 2010, the soybean plots will be rotated to corn for grain and vice versa.

One of the potential benefits of using legumes as the living mulch is their higher forage quality, especially crude protein, compared to crops like corn. By combining the two, you have a value added crop for fall grazing. In the corn grain plots, stover yields did not differ among the legume treatments ranging from 8.7 to 9.2 Mg/ha. Birdsfoot trefoil was the only legume that contributed significantly to fall forage yields averaging about 280 kg/ha.

Matsuda Farms is an organic operation that eliminates the possibility of using herbicides to suppress the living mulch. At this site, we harvested the initial spring growth as hay from an established stand of red, white, and kura clover. Following haying, we strip tilled down the center of each flood irrigation bed and planted millet for hay. Unfortunately, the clover came back too quickly and competed strongly with the millet, reducing yields. Following the second harvest for hay in late summer, we again strip tilled and planted winter triticale, a more aggressive plant that we think will compete well with the clover in the spring. We plan to harvest the triticale/clover mix for hay in early June of 2010, strip till again, and then plant a more aggressive summer annual forage like sudangrass or sorghum-sudangrass for hay.

Randy Hines, the other producer, decided to withdraw from the project, so we established a demonstration seeding at the Western Colorado Research Center at Fruita. This was a co-establishment study in which we first seeded a mix of red, white, and kura clover on the flood irrigation bed followed by planting of corn for grain. A strip of granular Harness herbicide was applied down the middle of the irrigation bed with the corn planter at time of seeding to control weeds and keep any clover from establishing in the center of the bed. This approach worked surprisingly well. We used a Buffalo brand no-till corn planter which we think we can easily modify to broadcast the clover seed, apply the granular herbicide, and seed the corn all in one pass. We plan to demonstrate this approach in 2010.

In 2010, we plan to work on fine tuning methods of suppressing the living mulches, especially the herbicide rates. Some of this work will be done in the greenhouse as well as under field conditions. This appears to be the part of this cropping system that may keep producers from implementing it. The living mulch must be suppressed so it does not compete too strongly with the annual crop thereby reducing yields. On the other hand, if you kill the living mulch, then it must be replanted which negates any advantage of using perennials for cover crops. From our experience to date, there is a fine line between suppressing and totally killing the living mulch. At the conclusion of the 2010 field season, we should have enough data to start putting together an economic analysis of the potential benefits associated with using living mulch cropping systems in the semi-arid western United States.

Impacts and Contributions/Outcomes

We are still too early into this project to have a good feel for how the information generated will ultimately affect producers in Colorado and other western states. We are fairly confident that we can establish most of the legumes evaluated so far using conventional cover crops such as oats or co-establishing them with corn for either silage or grain. The demonstration trial at Fruita in which we seeded a mix of clovers along with corn that was harvested for grain was very promising. The bottleneck for getting producers to adopt this cropping system appears to be figuring out how to suppress the perennial legumes without killing them once they are established. Two field tours were held in 2009, one at Fruita with 25 in attendance and one at Fort Collins with 14 in attendance. One presentation was given on the concept of living mulch cropping systems at an irrigation workshop with 17 in attendance. Producers are intrigued with the concept, but are waiting for more information before seriously considering the possibility of implementing such a system. If the economic analysis proves positive, then more producers should be interested in experimenting with the system.

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