Kale leaf nutrient density response to various mulches
The purpose of this study is to determine the impact of black plastic and two chipped slash mulch treatments on kale plant leaf nutrient density, and resolve key practical questions involved with using chipped slash as a mulch. Black plastic mulch has been a core component of our organic farms’ strategy for weed suppression and moisture retention in the soil. Removing this black plastic from our crops’ life cycle serves our organic farm’s goal of growing natural, nutrient dense, food in a responsible and environmentally conscious method without reliance on chemicals. In effort to eliminate black plastic from our crops’ lifecycle, yet continue growing nutrient dense crops, we are investigating chipped slash as a mulch alternative. Patrick Drohan, a technical advisor, has provided insight into field observations and data phenomena. Jeff Lackey, a consultant, has performed data collection and analysis.
Ramial wood chips were spread on four cultivated rows approximately 230’ long in 2016 and subsequently planted. Rows of black plastic were correspondingly prepared and planted. A local arborist was paid $50 for each load of fresh ramial wood chips delivered to the farm and dumped out in the vegetable field immediately adjacent to the rows. One dumptruck load (12+ yards) was sufficient to mulch one row, thus four loads of chips were purchased in 2016. A deep wheel barrow was used to transport the chips from the main dump site to a particular spot in a row. Half of a row was light mulch and half was heavy mulch. The light mulch treatment was established by spreading two wheelbarrows over 10’; the heavy mulch treatment by spreading three wheelbarrows over 10’. A hard rake was used to quickly shape the chips into a bed. All kale plants were started in trays in a greenhouse. Four rounds of trays, one round for each treatment set of light mulch, heavy mulch, and black plastic mulch, were started over the course of the growing season and transplanted once hardened-off and the weather permitted.
Round 1: Westlander kale transplanted May 23 in rows prepared May 22 (50% Maple, 50% Hemlock). Round 2: Westlander kale transplanted July 31 in rows prepared June 21 (90% Maple, 10% Pine). Round 3: Red Russian kale transplanted August 1 in rows prepared July 14 (100% Maple). Round 4: Nash’s kale transplanted August 31 in rows prepared August 21 (90% Maple, 10% Pine).
Brix data was collected periodically in July, August, September and October. A particular group of kale plants were tested once they were of a size appropriate for a harvested leaf to be juiced. The last session of Brix data collection occurred in the middle of October. Frosts in late October catalyzed physiological changes in the kale plants that prevented juice from being obtained for Brix testing via the juicing method utilized throughout the study. Soil samples were collected in August, September, and October from all test plots.
Data analysis and outreach pertaining to the first season of the grant are on-going. A second season of study is available with the grant.
Hot weather started in the second half of May and continued through the summer, creating growing conditions that were not ideal for kale. The Red Russian variety of kale, planted in early August, was similar in growth rate and final size across all mulch treatments, but for all other varieties of kale the plants in black plastic grew slower and never achieved the same size as that of the plants in the wood chips. Out of the four rounds of kale planted in black plastic, only the Red Russian kale grew to a size sufficient for profitable harvesting.
We found that using a tractor front loader bucket to move chips after they were dumped at the farm increased the likelihood that dirt and plant material was incorporated into the chips prior to spreading on the rows. Dumping the chips adjacent to the vegetable rows at delivery and filling wheelbarrows with shovels helped us keep the chips clean.