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The Garden Plot for February 29, 2008
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: "Weed Design"
We know that there are many tools and strategies for managing weeds; there is no one-tool-fits-all recipe. Our research over the past three years has shown that weed management is even more complex than we thought.
In our studies, we found that the yield and quality of a crop plant is influenced by much more than how many weeds are competing with it. Crop yield and quality are influenced by the crop plants’ soil and air temperature preferences and plant nutrient needs, as well as by the plant nutrients, soil health, soil and air temperatures, and plant competition we provide it with. In turn, the kind of weed management we employ affects soil health and insect and disease populations. Soil organic matter levels were lowest in all of the plots in which we used cultivation or tillage to manage weeds. Insect management with biological control was enhanced by our reduced tillage/living mulch system. It is hard to untangle this web of interactions in order to design the perfect weed management plan. The good news is that we can say with certainty: clean cultivation, bare soil between plants, a “weed-free” garden does not always produce the best quality and yield of crop plants. The bad news is that different crops with different temperature, nutrition, and soil health needs may require different weed management plans. This means more thought and stewardship on the part of gardeners and farmers.
The following is a practical summary of our research findings:
If your soil health is good, then cool season crop plants (such as lettuce and broccoli) can tolerate a lot more competition from other plants (such as weeds, cool-season crop plants, cover crops, and living mulches). Our studies have helped us to be relatively quantitative about what we mean by “good soil health”. It looks like organic gardeners and farmers need a soil organic matter level above 3% and nitrate-nitrogen levels above 40 ppm for soil health to be considered good. Early season nitrogen and phosphorus levels are part of this good soil equation. Apparently, the more nutrients available, the more there are to share.
Cool season plants can withstand plant competition even in soils with lower nutrient levels, as long as you warm soil temperatures. In our reduced tillage/living mulch system studies, we warmed the soil in crop rows with a new paper mulch product called Ecocover. Soil temperatures were highest in the paper mulch plots all season, yet they never went above 70 F even in July when air temperatures averaged 97 F. Yields in paper mulch plots were the highest when compared to plots that were hoed regularly, sprayed with vinegar, minimally tilled only once in the spring pre-plant, and plots that were no-till.
Warm season crops (such as tomatoes and melons) cannot handle as much plant competition in our cold climate, unless the soil is warmed a lot.
Tillage warmed the soil, especially in the early part of the season, better than no-till, minimum-till, and vinegar weed management plots. Yields were second highest, behind paper mulch, in tillage plots, but soil organic matter and nitrate-nitrogen levels dropped more in these plots than in paper mulch, minimum, and no-till plots.
Our studies show that weed management entails more than simply killing weeds. We don’t have all the answers yet, but we know that how we manage weeds can affect the whole garden or farm, from long term soil health to insect control.
Helen Atthowe's new short program of gardening tips
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