Nutrient-rich composted manures for Romaine lettuces
Livestock manure is a plentiful, renewable resource. Nearly 1.4 billion tons of it is created each year in the U.S. alone. Much of it is utilized as fertilizer on commodity crops, but what about using it on vegetables that often go straight from the fields and into hungry mouths?
A team from Morehead State University’s Department of Agriculture Sciences is looking at using manure-amended media to grow lettuce in a controlled agriculture environment (CEA) system. They discussed their study at a recent American Society for Horticultural Sciences conference.
Lettuce, one of the most popular and important leafy vegetables, tends to grow well in the field or in a CEA system. It grows under both passive and active hydroponic systems. So the Morehead State team developed a project to evaluate the application of composted manures on horticultural crops and their interaction with soil properties in CEA conditions in a greenhouse.
Three different types of composted manures (sheep, cow and horse) both with and without zeolite (a crystalline hydrated aluminosilicate mineral) were added in various proportions to PRO-MIX® BX All Purpose Growing Mix and used as the growing media for the seedlings of two Romaine lettuce cultivars (‘Salvius’ and ‘Amadeus’).
There were eight different treatments: 100% PRO-MIX; 80% PRO-MIX with 20% composted horse manure; 80% PRO-MIX with 20% composted cow manure; 80% PRO-MIX with 20% composted sheep manure; 95% PRO-MIX with 5% zeolite; and 75% PRO-MIX with 20% each of composted horse, cow and sheep manures and 5% each with zeolite.
The lettuce was seeded in six-inch pots, sub-irrigated and grown until harvest time in the greenhouse. Heads were harvested after two months, and fresh and dried yields were recorded.
After harvest, both the leaf tissue and the growing media were analyzed for chemical nutrients. The results from that first season showed significant differences among both cultivars and growing media.
It turned out adding zeolites had a positive effect on reducing ammonia emissions during the manure composting process and increasing the conversion to nitrates. (Nitrates come from nitrogen in the compost in a form that is more available to crops.)
Not only that, the team found that zeolites can improve the efficiency of nutrient use by increasing the availability of phosphorus from phosphate rocks.
‘Salvius’ lettuce thrived across the trials, with above-average head heights, widths, fresh weights, dry weights, leaf lengths, leaf widths and plant survival all around. ‘Amadeus’ didn’t have the big numbers ‘Salvius’ did, but its survival rates increased across the board as well.
Other notable results from the first-year trial included:
- Head height was above average with PRO-MIX by itself
- Plant survival was highest with 80% PRO-MIX/20% cow manure compost
- Head width and leaf length were above average with 95% PRO-MIX/5% zeolite
- Fresh weight and leaf width were above average with 75% PRO-MIX/20% cow manure compost/5% zeolite
- Average head height: 6.83 inches
- Average head width: 5.9 inches
- Average leaf length: 5.74 inches
- Average leaf width: 2.86 inches
- Average head fresh weight: 1.23 ounces
- Average plant survival: 1.4 (vs. 1.0)
It truly was a mixed bag when it came to which amendment combination worked best. The Morehead State researchers will be fine-tuning their experiment plan in the future.
by Courtney Llewellyn
