Sap, soil and tissue sampling with US cotton farmer Zeb Winslow
By Bec Sloane, US Communications Coordinator
Fifth-generation cotton producer Zeb Winslow keeps one eye on what is happening above ground, the other on what’s happening below. Based in Scotland Neck, North Carolina, Zeb has worked with the Better Cotton Initiative (BCI) over the past decade, forging on with his soil conservation journey.
Pioneering regenerative practices on the family farm, Zeb manages a rotation of cotton, corn and soy using multispecies cover crops and no-till systems. In other words: minimizing soil disturbance and planting species besides cash crops to retain moisture and nutrients, support microbial activity and suppress invasive weeds – lessening the need for chemicals.
Collaborating with agronomic consultants and cutting-edge labs, Zeb aims to better understand soil ecosystems, improve crop health and provide a roadmap for fellow producers.
His efforts are supported in part by innovation funds from BCI, in tandem with the Soil Health Institute (SHI) and ag-tech provider Growers Guide, with whom Zeb has worked for years to analyze the impacts of farm practices on his soil and yields:
“Working with farmers and collaborators like BCI and SHI makes the feasibility of the data collection part of research achievable and actionable. Being able to learn what’s going on in the soil and plant in-season and tying that to trends in harvest data really helps focus in on key trends that show up. We can then take those learnings to other farms.”
Justin Taylor, Sr. Sales Manager at Growers Guide, joined Zeb and BCI’s US Impact Manager Karen Wynne last month to mull over findings from the field tests performed in Zeb’s fields this past growing season.
Photo credit: Zeb Winslow | Better Cotton Initiative, 202
“What are we really chasing here?”
Together, the team is measuring the biology and functionality of the land Zeb farms through soil, plant tissue and plant sap sampling – akin to a blood test for crops, providing real-time insights into nutrient availability. With the results, they are assessing how to hone in on trends moving forward.
The question of the hour: Which is more predictive of yield success – steady balance or high levels among nutrients?
Justin observed that in Zeb’s cotton, soil and sap tests correlated to the balance across nutrients contributing to better yields, yet tissue samples told a different story, indicating that “more is more” (higher potassium and phosphorus levels linking to higher yields). Deferring to the soil and sap, Zeb opted for prioritizing nutrient balance over fertility levels, ensuring his cotton gets what it needs – when it needs it – throughout the growing season.
One thing at least was indisputable from the analyses: Across the board, biological markers (organic matter and specific nutrients being measured) indicated higher values where synthetic fertilizers were not being spread.
“We would have been more surprised if it went in the other direction!”
Though expected, Zeb noted that this was nonetheless a good sign, illustrating the most significant change among plots being tested. All in all, positive trends were seen, specifically among the cotton, but too little consistency could be gleaned across all crops to prove valuable to the data set being assembled.
“The next step,” Justin explained, “is to use the research we have done so far and focus more this growing season on how nutrients are moving among sap, soil and tissue – and compare how that movement differs between where we are spreading commercial fertilizer, and where we are not”.
Photo credit: Zeb Winslow | Better Cotton Initiative, 2025
Painting a fuller picture
More value, it seems, is to be found in taking samples in-season, rather than just before or after; despite higher initial costs, findings could lead to less spending down the line.
Likening tissue analysis to a gas gauge – how much you have in the tank, how much is being stored – Zeb suggests sap analysis is more the speedometer, relaying what is currently occurring within the plant. Each is telling in its own right:
“You could be predicting a problem down the road or something already serious; working in tandem we can learn more.”
Sap testing is still the newer, less utilized tool in the toolbox, but – combined with soil and tissue analysis – can tell a more complete story of all that is happening at once: how nutrients move from soil to plant, and at the end of the season, how they return to the soil.
A world of difference evidenced in living roots
The Winslows’ farm moved away from conventional tillage 30 years ago. In the last 15, Zeb transitioned that operation to 100% no-till with multispecies cover crops on all acres.
For a time, despite the myriad benefits cover crops provided – a boost in soil health, soil biology, profits and sustainability – they were also generating an overabundance of aboveground biomass. Again the idea of “more is better” was presented, but Zeb found “that type of population was causing problems for us.”
As he demonstrated while presenting at BCI’s Large Farm Symposium 2026, Zeb was able to better establish cover crops on rows that match his planting patterns. With increased spacing and GPS guidance, he could plant his cotton between the rows of cover, greatly reducing interference. This also led to cover crops growing larger – both aboveground and below, revealing an important discovery: the larger root systems appear to be improving soil structure, microbial activity and the amount of life Zeb is seeing in his fields.
In his cotton plot, one can pull up healthy, 10-12″ tap roots – if not longer.
The root system of a three-inch tall rye seedling, one of Zeb’s cover crops. Zeb: “This still amazes me that a plant that small can have roots four times the length of the aboveground growth.” Photo credit: Zeb Winslow | Better Cotton Initiative, 2025
Photo credit: Zeb Winslow | Better Cotton Initiative, 2025