Working towards healthier crops
Soil and nutrients play a vital role in growing high yields of quality vegetables. Pest management is also essential.
As part of the special Integrated Pest Management (IPM) Workshop on cucurbits at the latest Great Lakes Fruit and Vegetable Expo in Grand Rapids, Mich., two specialists shared their insights. Elaine Roddy, vegetable crops specialist, Ontario Ministry of Agriculture, focused on soil quality, while Darryl Warncke, soil fertility specialist, Michigan State, discussed nutrient requirements. Because these factors are interdependent, both must be addressed for optimum productivity.
Fortunately there are steps growers can take now, during the fall, to enhance next year’s cucurbit crops.
Healthy crops need healthy soil
Roddy pointed out, “IPM tends to focus on insects, diseases and weeds, but soil quality is a cornerstone of a good IPM program. A healthy crop starts with healthy soil. She added, “A healthy, vigorously growing crop is significantly less susceptible to pests such as seed corn maggot, wireworm, seed decay and root rots.”
She related an instance of bacterial speck where the plants had no root system. Roddy outlined ways for improvement to a large assemblage of growers at the workshop.
Importance of organic matter
Organic matter plays a key role in soil structure, fertility, drainage, aeration, nutrient cycling, moisture holding capacity and in reducing erosion.
The correct level of organic matter depends on the soil type. Roddy indicated that the optimum for sandy soil ranges from 2 to 4 percent, sandy-loam, 3 to 4 percent, loam and clay-loam, 4 to 5 percent, and clay from 4 to 6 percent.
Practices such as rotation, soil amendments, cover crops and tillage can manage organic matter.
“When roots go down, yields go up,” Roddy stated. She stressed avoiding soil compaction, particularly with heavy equipment, and working wet soil. Excessive seedbed preparation can create problems.
“Soil compaction is a function of total axle weight, especially in deeper soil layers,” Roddy explained, reporting Greg Stewart’s observations. Ideally, loads should be limited to 5 tons per axle. Also, use radial tires with pressure less than 15 PSI. With heavy harvesting equipment, create permanent rows using GPS technology. She advised assessing the soil, taking a benchmark sample with a soil probe, then making necessary adjustments.
Rotating cucurbits with deeper-rooted crops such as soybean, corn, wheat and alfalfa will help relieve soil compaction. The roots of the vine crops can more easily locate water and nutrients by penetrating the root channels left by the previous crop.
Many vegetable crops leave little residue in the soil. Rotating these with a high-residue, high-carbon/nitrogen crop helps maintain organic matter while protecting against erosion and providing nutrients for the next crop. Avoid the same crop family, of course. Fusarium, phytophthora, scab, alternaria, anthracnose and gummy stem blight, which affect cucurbits, can be lessened by following a proper crop rotation regime. Melons, for example, have shown significantly less fusarium after winter rye.
Organic matter is bolstered by manure. In addition to nitrogen, phosphorus and potassium, many manures also contain micronutrients, including boron, calcium, copper, iron, magnesium, manganese and zinc. While researchers do not yet know how readily available these micronutrients are to the plants, over time they will improve soil fertility.
The amount of biomass added by fall- planted cover crops such as flowering oilseed radish can amount to as much as 10,000 pounds per acre. In addition to providing nitrogen, oilseed radish and several other cover crops, including cutlass mustard, plus some sudans and sorghums, millets and marigolds, suppress nematodes.
Roddy cautioned that cover crops can help improve soil quality but do not replace proper rotation.
No-till systems provide the most organic matter and leave the highest amount of protective crop residues.
Roddy pointed out that zone tillage (strip tillage) can combine the best of both no-till and conventional tillage systems. Using both shanks and coulters to create an 8 to 12-inch-wide zone of tilled soil can create a desirable seedbed. Since the area between the rows is undisturbed, surface residue is left, while the seedbed itself is fine. Zone tillage may be performed in the fall. Pumpkins especially benefit from zone tillage, and also work well in no-till into a rye cover that has been rolled.
Attributes of healthy soil
Roddy described healthy soil as having good structure, minimal compaction and abundant earthworms. However, since earthworms dislike sharp sandy soils, the number of earthworms does not necessarily indicate quality. Healthy soil resists crusting, smells good and readily decomposes residue. Further, it has good drainage, water movement and water-holding capacity. Healthy soil also encourages seedling emergence and promotes deep root growth. With optimal nutrients, pH and organic matter levels, the soil produces uniform crops with rich color. In addition, healthy soil resists erosion by wind, water or tillage.
Good root systems boost yields
Warncke echoed Roddy’s research on soil quality. He reported that soil conditioned by effective crop rotations and by cover crops that build organic matter provide a favorable environment for cucurbit roots. He suggested using a mixture of cover crops and noted that legumes and brassicas especially contribute to fertility. Warncke, too, cautioned against compacting the soil and encouraged growers to continually check for compaction. “Minimize disks and moldboard plows,” he advised his large grower audience. “Till only when the soil is friable.”
Nutrient management demands knowledge
“The first step to establishing and maintaining good soil fertility is to sample the soils in each field and have them analyzed,” Warncke stressed.
Cucurbits can use the nitrogen released from organic matter. A legume cover crop, Warncke said, can supply up to 80 pounds per acre. Consequently, nitrogen needs to be adjusted. Following a legume crop cover will likely reduce the next crop’s nitrogen requirement by about 40 to 60 pounds per acre. With a corn crop or an 8-inch cereal crop, 20 pounds additional nitrogen per acre may be required for the next crop. Following wheat can demand 40 more pounds per acre.
Warncke cautioned, “Excess nitrogen stimulates vegetative growth at the expense of fruit set and development.” He pointed to several management tools to help growers assess the amount of nitrogen in the soil, including a preplant soil nitrate test, a chlorophyll meter and a petiole sap test.
Importance of proper pH
Warncke emphasized that for cucurbits, maintaining a pH between 6.0 and 6.5 is imperative. Allowing the pH to decrease below 6.0, he said, can adversely affect crop yield and quality. The pH affects nutrient availability, particularly phosphorus and manganese. However, soil pH in the 6.0 and 6.8 range can improve the availability of calcium and magnesium. Warncke included a number of corrective actions. For example, maintaining adequate soil moisture helps minimize blossom end rot, which is associated with inadequate calcium reaching the end of the young developing fruit. He said that foliar application of 2 pounds calcium and/or magnesium per acre per application can provide some in-season benefit, but long-term application needs to come from soil application. He recommended the rate of 20 to 50 pounds magnesium and over 100 pounds calcium per acre.
“Lime when needed,” Warncke urged. In some fields, he cautioned, the pH may be variable. Acid spots may develop. Also, pH changes occur more quickly in sandy soils. He advised, “When lime is needed, apply it at least three months, preferably six months, prior to crop planting.”
Agricultural lime must be used, not gypsum. Warncke recalled an instance where cucumbers yielded only 4,050 pounds per acre without a lime application, 4,255 pounds per acre with gypsum, but 6,660 pounds per acre with agricultural lime.
Warncke concluded by urging growers to keep the soil in good condition with proper rotation and soil-building practices and to base the fertilizer on the nutrient needs of the crop and the nutrient status of the soil. He reiterated, “Be sure the pH is right.”
The Great Lakes IPM Working Group has a limited number of DVDs on the IPM Workshop presentations for a shipping and handling charge. Details on the characteristics of various cover crops as well as nutrient requirements and application rates are included for this soil and nutrients topic, plus numerous other presentations. Contact Jim Jasinski at Ohio State University Extension, IPM Program, at firstname.lastname@example.org.
The author is a writer-researcher specializing in agriculture. She currently resides in central Pennsylvania.