The effect of cropping rotation and management on arbuscular mycorrhizal fungi in a sustainable dairy cropping system
Open Access
- Author:
- Haider, Kristin Regina
- Graduate Program:
- Ecology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 17, 2014
- Committee Members:
- Roger Tai Koide, Thesis Advisor/Co-Advisor
- Keywords:
- arbuscular mycorrhizal fungi
canola
tillage
cropping rotation - Abstract:
- As concerns about biodiversity loss, soil loss, nutrient imbalance, energy use, and climate change grow, there has been an increasing effort to develop cropping systems that minimize these environmental impacts while remaining economically viable. Indicators such as crop yield and quality, weed and insect populations, nutrient conservation, greenhouse gas emissions, energy use and production, and overall farm profitability are commonly measured to assess the performance of these systems, but it is also important to consider the impact cropping systems may have on non-target organisms, especially those that play an important role in agricultural systems. One such group of non-target organisms is the arbuscular mycorrhizal fungi (AMF). We conducted two studies to examine the impact of cropping rotation and management on AMF within one such cropping systems trial that was developed to identify sustainable dairy cropping practices in the northeast United States. In the first study, oats (Avena sativa L.) were planted as a mycorrhizal companion crop for fall planted canola (Brassica napus L.), a non-mycorrhizal crop, to determine if intercropping oats with canola was an effective method of maintaining AMF populations. The colonization of corn (Zea mays L.) bioassay plants was assessed in plots of canola with and without oats as a companion crop after the canola was harvested. The colonization of the two crops following canola in the crop rotation, rye (Secale cereal L.) and soybeans (Glycine max (L.) Merr.) respectively was also assessed. There was no significant difference among treatments in the colonization of any crops assessed. The lack of the effect of oats as a companion crop may have been due to the oats being winter-killed prior to establishing significant biomass, or the low planting density (22.4 kg ha-1) of the oats. Alternatively, compounds produced by the canola plants, called isothiocyanates, may have suppressed the colonization of the oats by AMF. Therefore, intercropping canola with a low density of winter-killed oats does not appear to be sufficient method of increasing mycorrhizal colonization in crops following winter canola. Additionally, in the first study, the oat companion crop treatment was nested within an herbicide treatment that compared reduced and standard herbicide practices. The reduced herbicide treatment was tilled with a moldboard plow before canola was planted while the standard herbicide treatment was not tilled. Colonization of the corn bioassay plants, planted after canola was harvested, was significantly reduced in the reduced herbicide (tilled) treatment. There was no difference in the colonization of the subsequent two crops, rye and soybeans. There was also no interaction between the herbicide management treatment and the oat companion crop treatment. The rapid disappearance of the impact of tillage on AMF colonization in this cropping system suggests that sporadic tillage may have little consequence for mycorrhiza-dependent crops if they do not directly follow tillage in the rotation. The second study focused on the overall effect of crop rotation and management in the dairy cropping system on AMF colonization of corn grown within three rotations, a six-year grain crop rotation with an herbicide management treatment, a six-year forage crop rotation with a manure management treatment, and a two-year corn-soy rotation with a manure management treatment. The colonization of corn seedlings was assessed for all corn plots in the system when the seedlings reached the third leaf stage. Within the three rotations, I also made comparisons between management treatments including a manure management treatment (broadcast vs. injected manure), an herbicide treatment (reduced vs. standard herbicide), and a cover crop treatment (red clover (Trifolium pretense L.) vs. hairy vetch (Vicia villosa Roth) and oats). Overall there was no difference in the colonization of corn between manure management treatments, herbicide treatments, or cover crop treatments. Three different varieties of corn were used in the three rotations: one conventional variety, one variety with a single transgenic trait for herbicide resistance, and another with three transgenic traits including one for expressing the insecticide protein Bacillus thuringiensis (Bt). To determine if corn variety impacted AMF colonization, the three corn varieties were grown in a greenhouse in sterile soil inoculated AMF spores. There were no significant differences in the amount of mycorrhizal colonization of the three varieties. Although there was no significant impact of corn variety or treatments within the rotations on AMF colonization, corn seedlings in the corn-soy and grain rotations were colonized significantly less than those in the forage rotation. The observed differences in the colonization of corn among the rotations may have been driven by the presence of a cover crop preceding corn in the rotation. Because AMF are dependent on their host plants for energy, long periods during which host plants are absent or only poor hosts are present are detrimental to their populations. In the corn-soy rotation there was a fallow during the winter preceding corn, in the grain rotation there was a rye (a potentially weak AMF host) cover crop, and in the forage rotation there were alfalfa (Medicago sativa L.) and red clover/hairy vetch cover crops. Based on these results, it appears that the prior crop has the largest impact on colonization of corn by AMF in this system, and that cover crops that for strong AMF associations should be used instead of fallows and plants that form weak AMF associations to promote the colonization of subsequent plants.