Tamara ScullyWhile much of the focus is on getting crops in the ground, getting the ground ready for the crops should be a priority, too. No matter the crop, the proper soil properties, including fertility, can mean healthier plants and bigger yields.
Every crop has a critical uptake period, where its need for nitrogen and other nutrients is intensified. For hops, that period begins in late spring, as the plant begins to rapidly accumulate biomass. Until early summer, the hop plant is growing its vegetative portion, gearing up for its reproductive stages and rapidly consuming nutrients. Once mid-July comes, the plant’s critical uptake period ends and the need for nutrients levels off for the remainder of the growing season.
If adequate nitrogen is not available to meet the plant’s needs during this time, there will be consequences.
“Yields will suffer,” Dr. Heather Darby, University of Vermont Extension agronomist, said. “You want to make sure there is adequate nitrogen, and other nutrients, for your crops” during their critical uptake period.
While the Pacific Northwest has years of research, data and experience with hops, the crop is only recently being re-introduced to the Northeast, as a result of the craft brewing movement. Research at the University of Vermont’s hopyard is helping growers along the eastern seaboard to determine optimal parameters for hops growth in the region.
Fertile ground
The optimal pH for hops is 6.2 – 6.5. While the plant can grow and produce a crop between pH ranges of 5.7 and 7.0, the optimal range is where the most nutrients can be made available, enhancing plant health. Prior to the initial planting of the hopyard, liming to achieve this optimal pH range is highly recommended. Any pH levels outside of the optimal range restrict the nutrient availability to the plant. But liming to change pH takes time.
“If you’re getting ready to plant a new hopyard…please make sure you take a soil test before you put those plants in the ground,” Darby emphasized. “Once they are in the ground it becomes a little more difficult to make major corrections to soil fertility, especially pH. Get the lime in the ground before you put the plants down.”
An annual hopyard soil test is recommended. Soil samples are best taken two to three feet below ground in established plantings, or at a depth of one to two feet for new hopyards. The roots of the hops plant grow deep. Taking samples near the planting hills generates the best results.
Ideally, soil tests are completed in the fall and there should be five to 10 soil samples per acre. Separating the hopyard into different areas depending on soil types or other factors allows more precise fertility control. The samples from each designated area should be mixed together, with a sub-sample taken from this mixture and sent to the laboratory. The University of Vermont and Dairy One both have laboratories which offer soil testing for hop growers, generating recommendations based on test results and the crop’s needs.
Hop fertility needs
Nitrogen, potassium and phosphorous (NPK) — along with boron and zinc — play major roles in hop fertility. Boron and zinc are “easily lost in the soil” and are commonly deficient in the Northeast region, Darby said.
For every 1,000 lbs. of dry matter produced, on a per acre basis, the hops crop will need 30 lbs. of nitrogen, 20 lbs. of potassium and five lbs. of phosphorous. But the dry matter includes the entire vegetative growth of the hops.
Most growers aren’t weighing the total biomass of the crop, but only the cones. Cones require about one-third to one-half of the nutrients overall. By weighing the cones at harvest, the amount of NPK the plant utilized in order to have produced those cones can be calculated.
If a grower is desiring higher yields, the amount of NPK available during the critical uptake period will have to be increased, based on the plant’s requirement for each nutrient. Higher yielding hops varieties will have slightly greater nutrient uptake needs.
“If you want to have 1,000 lbs. of dry cones per acre, then you need to be fertilizing for 60-90 lbs. nitrogen to be removed from the soil” by the plant, Darby said. “Planning for some nutrient loss” due to runoff, leaching and denitrification is needed, increasing those amounts.
The actual amount of nitrogen added to the crop needs to factor in these potential losses. Soil type and weather will impact the degree of nutrient loss. Darby recommends split applications of nitrogen during the critical uptake period to minimize any environmental losses.
Fertilization of the hopyard can occur by broadcasting, fertigation or a combination of both. Fertilizer should be applied directly to the hops bed when broadcasting. If fertigation is used, small amounts of nitrogen, applied daily throughout the growing season, is recommended to guard against potentially elevating salt levels.
The amount of phosphorous needed for hops production ranges from four to seven parts per million (ppm). Potassium is needed at the rate of 100-130 ppm, and magnesium at the rate of 51-100 ppm for optimal hops growth.
When soil tests show results to be in the optimum level, “the chances of seeing a crop response from adding more fertilizer is pretty minimal,” Darby said. If results are above optimal, do not fertilize with that nutrient.
Other considerations
“I think you need to be adding organic sources of nutrients to your hopyard,” Darby said.
Organic source of nutrients, such as compost, manure or bagged organic fertilizer, are slow acting and the nutrients they contain are not available to the plant immediately. Because their composition can vary widely, compost and manures should be tested. Synthetic nutrients are available in real time for the plant to utilize, swiftly delivering nutrients.
Foliar nitrogen is not recommended for use in hops grown in the Northeast at this time, primarily due to concerns about downy mildew. Wetting the plant leaves via foliar applications of nutrients can increase disease pressures, which are already a concern in humid environments.
Petiole tests, while used in the Northwest, have not been researched enough in the production of hops in the Northeast to provide any guidance for hop growers at this time, Darby said.
Each season, hops require a large influx of nutrients, available during the crop’s critical uptake period, to thrive. Getting those nutrients to the plants involves field preparation prior to the initial planting of the hopyard, annual soil testing and properly timing the application of needed amendments. Factors such as weather, cultivar, soil properties and desired yields all factor into the equation.
The UVM “Hops Power Hour” webinar, focused on the fertility needs of hops, is available at www.youtube.com/watch?v=dDeN3S484cM.