Phosphorus Mobilization and Weed Suppression by Buckwheat.
Soil, soybean biomass, and insect samples were collected throughout the growing season on different locations in the Red River Valley of Minnesota. Buckwheat did not significantly increase the measurable soil P concentration at either location. However, the nutrient composition of the soybean plant was significantly different between treatments at both locations. These differences had no effect on grain yield. Buckwheat is very competitive and effectively eliminated weed competition. Several groups of beneficial insects were present in growing buckwheat. The Tachinid fly, green lacewing, and hover fly were the predominant beneficial insects.
To assess the value of buckwheat as alternatives to black fallow in the crop rotations of the Red River Valley to verify their value for 1) mobilizing soil P and other nutrients, 2) suppressing weeds, and 3) providing habitat to beneficial insects.
Buckwheat was established in 2001 as a green manure crop and incorporated after flowering but before seed set. Soil samples were taken prior to buckwheat establishment in 2001 and from the same sites (within one meter) in 2002 in the following soybean crop prior to growth stage, R1. Soybean plant samples were collected as the same time and analyzed for P, as well as several other common elements, from the two treatment areas. In the fall of 2002, grain yield was also measured. No other soil amendments were added during the trial.
Soil conditions were extremely wet in 2001 and 2002; floods or excessive rainfall destroyed eight of our research sites. In addition, the flooding and rainfall delayed planting and reduced the buckwheat biomass at the remaining two locations.
The soil P concentration increased significantly from 2001 to 2002 on both the buckwheat and fallow treatments. Buckwheat did not significantly increase the measurable soil P concentration at either location. Cluck (A commercial poultry manure, 4-4-2) was applied at both locations for the crop year 2000 and may explain a precipitous increase in P concentration between years. Soil pH increased and soil organic matter was reduced following buckwheat at the Olsgaard location.
The nutrient composition of the soybean plant was significantly different between treatments at both locations. At the Olsgaard location, plant P concentration increased following buckwheat despite no measurable differences in soil P concentration. At the Thomas location, buckwheat reduced the plant K concentration but caused an increase in Na and Zn concentrations. However, these differences had no effect on grain yield at either location.
Buckwheat is very competitive and effectively eliminates weed competition if an adequate stand is established. This was clearly the case at both locations.
Although several groups of beneficial insects were present in the buckwheat in 2001, the average number of individuals sampled within a species was low and did not vary across location. The Tachinid fly was the predominant beneficial insect across locations. The green lacewing and hover fly also occurred in greater numbers compared to most of the other beneficial insects. Data for 2002, which will determine their presence in the following soybean crop, is not yet available.
Impacts and Contributions/Outcomes
Buckwheat altered the nutrient concentration of the following soybean crop, but despite a trend for an increase in soil phosphorus concentration, we were unable to measure a significant statistical difference between treatments.
Buckwheat is an effective competitor with weeds if an adequate stand is established under normal growing conditions. However, weed pressure was not a serious issue in our locations.
Buckwheat is very effective in attracting different species of beneficial insects. However, their effect on the following soybean crop is yet to be determined; the data is still being analyzed.
Buckwheat is inexpensive to establish and offers many other benefits over black fallow. The potential benefits include quick establishment to prevent soil erosion, easy to destroy, and an excellent soil conditioner.