When Pasa Sustainable Agriculture launched its Soil Health Benchmark Study in 2016, it pitted no-till against tillage in the debate over which method is better, or worse, for the dirt.
Five years later, the study results indicate, surprisingly, that there isn’t a clear-cut winner.
Sure, no-till has the advantage, in part, because it doesn’t disturb the soil. But it turns out that farmers who do put a plow in the ground can be just as effective at achieving optimal soil health.
“Our study points in that direction,” said Franklin Egan, the report’s lead author and Pasa’s education director. “We found many instances of organic farms — vegetable and row crop — tilling pretty substantially but having good soil health scores.”
No Clear Winner
Working with Cornell University’s Soil Health Testing Lab, Pasa collected and analyzed soil samples and field management records from more than 100 pastured livestock, row crop, and vegetable farmers in Pennsylvania and Maryland.
In a recent report outlining the current findings of the ongoing study, Egan explains that continuous no-till’s reliance on herbicides to control weeds and terminate cover crops makes it a less than perfect method for achieving soil health.
Conversely, farms that relied less on herbicides and more on tillage to control weeds and prepare fields for planting were successful at maintaining soil health.
But the study finds that a balanced approach is critical when utilizing tillage, and says that cover crops, rotations, managing inputs and timing are key factors.
Tillage can weaken the stability of soil aggregates and deplete organic matter, but that can be offset by planting cover crops, incorporating perennials into the rotation, and allowing for fallow phases.
Vegetable farmers have had success adding fallow periods in clover. Row crop farmers might use multiyear stands of hay.
“This isn’t an endorsement of tillage as a good practice, but it can be successful when balanced with things like cover cropping and crop rotations,” Egan said. “You can maintain soil health with tillage.”
Pasture Integration Key to Healthier Soil
Though the study determined that both tillage and no-till are capable of achieving optimal soil health, they pale in comparison to the results on pastured livestock farms.
Maintaining deep-rooted forages for long periods builds the soil, and animals can enhance a crop rotation too.
“Pasture integration is the gold standard,” Egan said. “It gives a field a longer break, and it adds a balanced amount of manure and a lot of microbial activity.”
Still, Pasa’s report determined that manure and even the use of compost can be detrimental to soil health. Many vegetable farms in the study struggled with high levels of phosphorus in their fields.
Excessive nutrients increase the risk of runoff into waterways, and too much phosphorus can inhibit a plant’s ability to take in micronutrients, Egan said.
“Many vegetable farms supply nitrogen through manure and compost, and you’re going to have situations of excess phosphorus,” Egan said. “It’s an area in need of a fix.”
The answer, he added, comes back to crop rotation. Adding a legume to the rotation reduces the need for nitrogen from manure. Inputs such as feather meal, peanut meal and soybean meal could also deliver nitrogen without overdoing it on phosphorus.
“Manure has its benefits, but it’s best not to have to rely on it each and every year,” Egan said.
The study also covered the effect of climate change on soil health.
Egan referred to record rainfall in 2018 as an example. Researchers observed a 60% and 54% drop in aggregate stability on row crop and vegetable farms, respectively, in Pennsylvania and Maryland.
Most of the farms were able to partially or substantially rebuild their aggregate stability the following season, which offered more amenable weather and field work conditions.
But extreme rains and consistently wet seasons are expected to increase as the climate warms, so building erosion-resistant soil will be imperative for farmers.
“Too many years like 2018 in a row would be really hard to deal with,” Egan said.
Funding from the William Penn Foundation, the Hillman Foundation, the Pennsylvania Department of Agriculture, and a USDA Conservation Innovation Grant will keep the study going, and Egan hopes it will run for at least 10 more years.
“The recent report is the tip of the iceberg. A big hope is farmers look at our data and see the possibilities that are out there,” he said. “This is something every producer can get behind, and our data shows there are a lot of pathways to get to optimal soil health.”