Soil Health Management Practice Impacts on Soil Health on Vegetable Farms

For this project, individual farmers proposed trials that involved soil sampling to robustly answer research questions they have about novel or existing farming practices. In 2025, three farmers initiated multi-season trials. Two other farmers will initiate trials in 2026, which may become multi-season trials depending on initial results. We applied for and received a no-cost extension for this grant through August 2027, which will allow farmers to complete their multi-year trials. 

One participating farmer has implemented an extended rotation on their farm that includes 1-2 green fallow years on their existing beds and in are they are bringing out of pasture. Soil compaction is a concern on their farm and in their trial, they are seeding different diverse cover crop mixes and measuring soil compaction using a penetrometer before cover crop planting and before cover crop termination or winter. They have marked spots within their cover crop plots that they return to each time they collect data for the project. 

Another participating farmer has long been curious about using legume cover crops to provide nitrogen to her organic vegetable crops. She is aware that legume covers should generally be allowed to grow until they flower to provide maximum N credit. However, legume flowering happens later than most vegetable crops are generally planted in Iowa. The farmer has planted a randomized and replicated trial with two cover crop treatments, vetch + rye and barley + pea, which in spring 2026 she will terminate "the right way" (after legumes have flowered) and "when is best for me" (several weeks earlier in preparation for cucurbit transplanting). She will sample cover crop biomass at termination for C and N content as well as sample soil for soil nitrate content several weeks after termination. She may also include sampling of cash crop petiole N. 

A third participating farm is a diversified vegetable farm with integrated livestock. They are conducting a trial to investigate whether there is a significant difference in soil nitrate N in plots where cover crops were grazed prior to planting vs. plots where cover crops were mowed and manure was spread manually. They planted a cover crop in Fall 2025 and will conduct initial soil nitrate measurements and implement grazing/mowing treatments in a randomized and replicated design in March or April 2026. They will then prepare the site for brassica planting and measure soil nitrate when their brassicas are about to head. They may also include analysis of brassica tissue N content. 

Two additional farms are currently planning trials that will begin in the 2026 growing season. The first farmer will be acidifying the irrigation water in a high tunnel using an in-line fertigation setup and citric acid to determine if that is a viable method for controlling salts in her soil. She grows in her high tunnels continuously and has significant issues with high salts. As of Feb. 2026, she has conduced soil sampling to determine soil chemical attributes before implementing treatments (citric acid vs. regular irrigation water) and has also determined the pH and alkalinity of her irrigation water. She will implement her irrigation water acidification treatment in March and will track soil pH over the course of several months using a handheld probe. At the end of the growing season, she will conduct soil sampling to determine if there has been a change in salinity.

Finally, one farm is currently developing a protocol for a trial on the effect of summer tarping on soil pathogens that affect brassica crops. These farmers struggle with brassica diseases and have adopted a practice of growing both their spring and fall brassica successions in the same beds so they can rotate the beds out of brassica production for longer (4+ years). They tarp in the mid-summer between the two brassica successions and have observed some success with reducing disease pressure using this method. They are curious to see if there is a measurable effect of tarping on the abundance of the soil pathogens affecting their brassica crops.