Improve photosynthetic potential | Local farm
Farmers don’t often think about how their management practices can influence the rate of photosynthesis. Photosynthesis has always been assumed to be constant, but it is not. Photosynthesis does not occur at a constant rate, it varies every second, depending on light, carbon dioxide (CO2), water availability, temperature, chlorophyll content of leaves, l microbial impact on plant nutrient availability and genetics. Some factors can be manipulated directly, others indirectly. Many of these factors, but not all, can be managed by farmers to improve yields.
In any given year, the water can either be limited or in excess, while temperatures can also be extreme, either too cold or too hot. These factors often shorten the nutrient cycle, resulting in decreased plant growth and yield. Compaction and poor soil structure can have a direct impact on microbial activity, plant nutrition, water availability, soil temperature and CO2 storage. Fall tillage is a major disruptor of the carbon and water cycle. Every time a soil is plowed, CO2 is lost to the atmosphere within minutes and most of it eventually settles in our oceans. Most of the nutrients released by tillage are also lost, either in surface water (eg nitrogen or phosphorus) or in the atmosphere (nitrogen). The best way to preserve carbon and nutrients in the soil is to plant fall cover crops, thereby restoring the natural life cycle.
When the soil environment and crop nutrition are optimized, plants can photosynthesize much faster than what is generally considered normal. An extreme example comes from the Dutch greenhouses where tomato yields reach 890,000 pounds (445 tons) per acre or 20 pounds of tomatoes per square foot. Yields of field tomatoes in the United States range from 20 to 50 tons per acre. Greenhouse growers have the ability to manipulate lighting, CO2 levels, plant nutrition, and genetics to maximize crop yields. Farmers may not be able to manipulate lighting directly, but crop density, population and spacing can be manipulated. Farm management practices have a direct impact on CO2 levels, microbial activity, plant nutrition and genetic potential.
Farmers often manipulate their fields to produce lower yields by creating difficult and stressful field conditions. Farmers can also improve the soil environment, increase the rate of photosynthesis, and improve yields by creating a healthier soil environment. Adding cover crops increases carbon sequestration and increases plant root turnover, leading to more CO2 for plant growth. About 60-80% of all plant carbon is recycled and only 20-40% is stored in the soil. Carbon sequestration is a slow process, but it improves soil aggregation, drainage and higher microbial activity leading to greater availability of nutrients.
For example, in corn production, it takes 100 pounds of CO2 per day to produce 200 bushels of corn. If all the CO2 came from the atmosphere (at 410 ppm CO2), it would take 32 cubic acres of air per acre of corn to achieve this result. However, as plant roots take up oxygen and exude CO2, the atmospheric CO2 concentration in the soil increases to 3000-10,000 ppm CO2. Cool nighttime temperatures further increase soil CO2 levels to 20,000-30,000 ppm, which provides most of the daily CO2 requirements for plant growth. This CO2 level is only 10-20% of our possible full photosynthesis rate. To achieve major improvements in crop yields, researchers estimate that farmers need to improve their photosynthesis rate above 60% from our current photosynthesis rate of 10-20%.
Unfortunately, getting your soil into shape with cover crops and reduced tillage can be a slow process. It usually takes 3 to 7 years to make the transition. Soil health is a journey that takes time to be successful. The soil carbon at the soil surface increases first. Soils begin to aggregate or get better soil structure so that water can seep in. Then your soil will start to hold more water and the added carbon will sequester or hold more nutrients from the soil. This leads to environmental improvements in air and water quality.
As the rate of photosynthesis improves, the exudation of the roots increases, which feeds the microbes and improves the nutrient cycle. With higher rates of photosynthesis, plants become healthier, so pests and diseases decrease. Healthier plants can grow faster and reduce weed populations due to increased competition for light and soil nutrients. Healthier plants and soils respond better to microbial inoculants and low-salt fertilizers. In general, healthier plants produce more lipids (fats) and the grain has a higher nutrient density; all of this leads to much higher crop yields. The end result is that improving soil health leads to better yields, higher profits, and higher quality nutrient-rich foods while protecting the environment.