Evaluating functional diversity in an organic intercropping system

Evaluating functional diversity in an organic intercropping system

Summary

An incremental increase in functional crop diversity in an organic intercropping system may enhance ecosystem functioning and crop resource-use efficiency while improving or sustaining crop yields and fruit quality. Preliminary data suggest that intercropping combinations utilizing watermelon reduce soil temperatures and promote short-term soil moisture retention, thereby alleviating stress on crops during the peak of the summer heat in Texas. Additionally, weed dry biomass was significantly reduced and fruit quality does not appear to be adversely affected by multicropping treatments. Data are currently being analyzed to assess the benefits of plant functional diversity on soil health.

Objectives/Performance Targets

1. To examine the relationship between functional diversity and soil chemical (organic matter content, total and organic soil C and N) and physical properties (soil moisture, soil temperature)
2. To examine the relationship between architectural complexity and nutrient-, radiation, and water-use efficiency
3. To determine how incremental increases in functional diversity affect weed suppression and disease incidence and severity
4. To evaluate the effectiveness of intercropping systems on sustaining or enhancing crop yield and quality
5. To incorporate this research into the student-led Aggie Green Fund Organic Farm which is geared toward education and research

Accomplishments/Milestones

Objective 1: Soil sampling and measurements from year two of the study have concluded. Soil C and N analyses as well as organic matter content will be conducted in the coming months. In year two, analysis of soil microbial biomass, root biomass, litter quality and quantity and aboveground biomass estimates were added to enhance data on soil dynamics. Soil microbial analysis has concluded, but all other data is currently being or will soon be conducted. Preliminary results will be presented at Ecological Society of America’s annual meeting in August 2013.

Objective 2: Photosynthesis and water potential data were again collected in 2012. Photosynthesis measurements were taken at time of flowering for each crop and again when canopy cover was at its highest. Plant tissue analysis of 13C and N will be conducted in the coming months to determine water- and nutrient-use efficiency. In 2012, additional measurements of leaf area index were taken to examine radiation-use efficiency.

Objective 3: Conditions in 2012 were more conducive to disease occurrence than in 2011. As a result, downey mildew became an issue on watermelon. Estimates of downey mildew occurrence and severity were made. Weed biomass was collected toward throughout the duration of the study in 2012.

Objective 4: Yield and fruit quality measurements concluded at the end of the growing season in 2012. Data are currently being analyzed.

Objective 5: Due to competition with okra and disease problems, watermelon yields declined dramatically in 2012. As a result, there was very little marketable watermelon produced. Howdy Farm, the student-led on campus organic farm, had also met its supply of other component crops, namely okra and pepper, and was consequently not supplied with any crops utilized in this study. Therefore, there was no exchange of labor for marketable produce in 2012 with Howdy Farm.

Impacts and Contributions/Outcomes

The initial findings from 2011 data indicate that utilizing a functionally diverse cropping system has the potential for alleviating heat and moisture stress on crops during the peak of the summer heat in Texas and the southern region. However, because of differences in planting dates and disease issues in 2012, watermelon was not as prolific and may have not performed as effectively as a shade crop. This data is currently being analyzed. Preliminary results from soil microbial biomass analysis in 2012 suggest a reduction in microbial biomass carbon with an increase in plant diversity, contrary to what was hypothesized. Additional soil and root trait analysis is currently being conducted to help explain these results. In 2011, weed biomass was significantly reduced in cropping combinations containing watermelon. However, due to the aforementioned issues with the 2012 watermelon crop, it was less successful as a smother crop in 2012. As a result, the only crop that benefited from the weed-suppression effects of intercropping when compared to its monocrop was pepper. This highlights the importance of planting date as it relates to seedling establishment and competition for resources. Although data analysis is ongoing, initial results from both years suggest that introducing a functionally diverse cropping system and appropriate planting dates could translate into a reduction in manual labor and costs for organic producers in the southern United States through weed suppression. Upon conclusion of data analysis, the benefits of these systems on soil health and the potential to reduce fertilizer and irrigation inputs for small-scale organic producers will be determined.

Collaborators: