Comparison of organic management systems and crop rotations
Foxtail demography
Velvetleaf invasiveness in various cropping systems

The VICMS research plots are the site of two studies to further understand how weeds invade and/or persist in different cropping systems, including organic systems.

Comparison of organic management systems and crop rotations

An experiment was initiated at SWROC in Fall 2002 to identify the costs and benefits associated with integrating additional crops and management practices into organic crop rotations. Comparisons between the systems in this study are expected to determine:

a) if compost use will reduce weed populations or improve soil quality, compared to manure use

b) if rotary hoeing can be made more effective with weed emergence models

c) whether the inclusion of fall cover crops after row crops reduces weed populations or improves soil quality

d) whether extended crop rotations have lower weed populations than shorter crop rotations

The experimental treatments will consist of two organic management systems and two cropping sequences. The two cropping sequences are corn-soybean and corn-soybean-oat-alfalfa. The two management systems differ as follows:

Weedcast is a temperature- and crop- driven model that predicts emergence patterns for several weed species. It will be used to schedule rotary hoeing passes for when 30% and 60% of the major weeds have emerged.

Weed populations will be evaluated using two approaches. First, weed seedlings will be counted in late June in corn, soybean and oat, and before each cutting in alfalfa. Secondly, weed seed production will be measured in fall in giant and green foxtail, which are the predominant weed species at this site.

Grain yield (corn, soybean and oat) and biomass (alfalfa) will be measured at harvest. Alfalfa protein content will also be determined after each cutting. Soil fertility will be measured in the fall and spring, and used to recommend manure and compost application rates, respectively.

Foxtail (Pidgeongrass) demography. The foxtail (Setaria) species are annual weed that are common to most farms in the Upper Midwest, including those that are under organic management. Although cultivation during the seedling stage is the most visible form of controlling those species, little is known how management of other foxtail life-cycle processes affect long-term population growth or decay.

Research was initiated in 2002 in the organic plots in VICMS to understand how differences in organic management practices (see Comparison of organic management systems and crop rotations) affect the risk of foxtail survival during different life stages.

Giant, green and yellow foxtail populations will be monitored year-round to determine the effects of organic management practices on transition rates in the foxtail life cycle. Examples of transition rates include: seedbank survival, seed germination (recruitment), seedling survival, seed production (fecundity) and seed predation (biocontrol). Due to the intensive labor required for measurements, research is limited to the corn-soybean-oat-alfalfa rotational system. Data will be collected from each crop within the rotation.

The dataset from this experiment will be used to develop practical models that can be used to assist basic management decisions, for example:

1. To what extent does each transition rate determine the population growth rate? How important are variations in each rate to population survival?

2. When do surviving or invading weeds pose the greatest risk during a season or crop rotation? What transition rates should farmers be most concerned with monitoring and disrupting?

3. How do different crops affect weed transition rates? What cropping sequence will cause the most rapid or efficient reduction in a weed population? Is the same shift in a transition rate (e.g. recruitment) desirable in all crops?)

4. What is the practical extent to which each transition rate can be manipulated through management practices?

Insight developed from the models will help farmers to minimize unnecessary tillage, identify whether seed germination should be discouraged in some crops (but encouraged in others), and whether fall cover crops may reduce the weed seedbank as well as contributing biomass or nitrogen to the soil. Finally, models will be used to more effectively target weed monitoring programs at critical periods during the life of foxtails.

Velvetleaf invasiveness in various cropping systems. Velvetleaf (Abutilon theophrasti Medicus), also known as buttonweed, is common in southeastern Minnesota, and is slowly spreading westward. In order to understand the impact that velvetleaf may have on various cropping systems in western Minnesota, velvetleaf was introduced into small sections of the VICMS plots in Fall 2003. Cropping systems included in the study were high-purchased input (HPI), low-purchased input (LPI), no-purchased input (NPI) and organic (ORG). In addition, velvetleaf was seeded into restored tallgrass prairie. The particular practices used in each cropping system are listed below:

As in the foxtail demography experiment, the effect of each cropping system on the velvetleaf life cycle will be measured. Evaluated processes will include seedbank persistence, seed germination, seedling survival, seed production and seed predation. These data will be used in population models to understand how each facet of the different management systems encourages or discourages velvetleaf invasion.

Invasiveness depends not only on persistence in one location, but also movement across the landscape. Establishment of velvetleaf beyond the introduction area will be monitored in each plot. These data will be used to estimate the velocity with which velvetleaf patches may expand to affect other field sections.

Data from this experiment will be used to identify the overall susceptibility of each cropping system to velvetleaf invasion. It will also be used to understand how differences between systems contribute to their susceptibility. These understandings will allow the modification of each cropping system to minimize its vulnerability.