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Improve Hydroseeding Success By Breathing New Life into Barren Soils

by Greg Northcutt

Given the unpredictable nature of rain, drought, heat and cold, getting grass or other plants to grow and thrive on construction or land reclamation sites is tough enough. Pressure from land developers and project owners to keep costs to a minimum doesn’t help, either. But, add in the unfavorable soil conditions typically found on these jobs and achieving success in seeding, whether to produce an attractive residential landscape or revegetate an eroded hillside, can be a daunting challenge.

In a subdivision near Washington D.C., two adjacent residential properties were hydroseeded the same day - one included a mix of growth stimulants, the other did not. After 22 days, site 1 (above), which was treated with a liquid-lime growth stimulant, produced a thicker stand of turf than site 2 (below), which was not treated.

In many cases, for example, the site has been shorn of topsoil and its complex community of microflora and fauna that nourishes and sustains plant growth, leaving behind unhealthy soils with little or no biological activity. In addition, the poor or barren soils that remain have often been compacted by construction equipment traffic, squeezing out the voids and pores that allow life-giving air and water to seep into the soil and provide spaces for plant roots to develop and grow.

“You can plant the best seed available and still get pretty shoddy results because of poor soil conditions,” says seed distributor Jim Claxton, Ellicott City, Md., a representative for Newsome Seed Inc.

That’s where soil amendments – soil conditioners and fertilizers – can save the day. Whether natural or manufactured, they can improve seed establishment and growth by altering the physical or chemical properties of the soil. Conventional soil conditioners consist of inorganic materials, like gypsum, lime and vermiculate, as well as organic substances, such as biosolids, compost, and sphagnum peat.

The choices also include a new generation of environmentally-friendly hydraulic mulch additives that can restore the health of ailing soils. Offering the speed and ease of a spray application, they require no incorporation. That’s another big advantage in today’s hydroseeding market where fewer and fewer project owners are willing to pay the extra cost of mixing amendments into the soil.

“Soil conditioners can set you apart from contractors who don’t use them by making your results look a whole lot better in marginal soil conditions,” he says.

Amending the Soil
When budgets and project parameters allow, inorganic soil conditioners can improve the soil by increasing water infiltration, retention and drainage and enhancing aeration and structure. Organic amendments also provide food for bacteria and fungi that enrich the soil with more plant food and improve soil structure. Some organic-based hydraulic soil conditioners also include bacteria or fungi that encourage soil microbial activity.

“The objective of adding organic amendments is to build up soil organic matter levels to make subsoil at a disturbed site more like a topsoil,” says David Walker, a revegetation and erosion and sediment control consultant, based in Calgary, Alberta.

Soil organic matter consists of animal and plant remains in various stages of decomposition plus the fungi and bacteria that feed on them. As University of Wisconsin extension specialists point out, organic matter performs several vital functions.

An important source of plant nutrients.
Decomposing organic matter provides significant amounts of nitrogen, phosphorus and sulfur along with other plant nutrients. Organic acids released as organic matter decomposes help to release nutrients from the mineral portion of the soil. Decomposing organic matter also attracts and holds inorganic elements, like potassium, calcium, magnesium and some micronutrients in forms that plants can readily use and prevents them from leaching.

Improves soil structure.
Microorganisms produce sticky materials that bind tiny clay particles into larger aggregates that do not break down easily when wet and resist compaction. The small pore spaces within the aggregate hold moisture, while the larger spaces between aggregates improve aeration and water infiltration and drainage

Increases moisture-holding capacity of soil
Like a sponge, organic particles absorb and hold water.

A relatively new class of amendments – super-absorbent co-polymers – can help manage soil moisture to ensure that plants receive water at critical stages of establishment.

In addition to their use as a flocculant in removing suspended soil particles from runoff, anionic polyacrylamides (PAM) can also be used as a soil stabilizing amendment to bind soil particles into stable aggregates, reducing soil erosion and creating voids in the soil to improve water infiltration.

When budgets and project parameters allow, inorganic soil conditioners can improve the soil by increasing water infiltration, retention and drainage and enhancing aeration and structure. Organic amendments also provide food for bacteria and fungi that enrich the soil with more plant food and improve soil structure.

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Other organic soil conditioners, like soil bacteria, humic acids, kelp extracts vitamins and enzymes, stimulate biological activity which promotes root growth and nutrient uptake. Humic acid, for example, increases the soil’s cation exchange capacity to provide nutrients in a readily-available form for plants, while kelp extracts contain growth hormones which promote cell division and larger root systems.

Innoculating soil with mycorrhizal fungi (endomycorrhiza for turf) offers another natural way to stimulate plant growth. These microorganisms live in a symbiotic relationship with the roots of most plants. The plant provides energy for the fungi. In return, the fungi send out fine threads called hyphae that probe into decomposing organic matter and send nutrients back to the roots of the plant.

Adding soil amendments - conditioners and fertilizers - to the landscape through hydroseeding can help enhance seed establishment and growth.

A Test of Performance
Soil testing to measure soil nutrient, pH and organic matter levels can help in selecting soil amendments appropriate to a given site. At the same time, it’s also important to understand the characteristics of the soil amendment, itself. “Whether it’s a natural material or a manufactured product, you need to know what’s in it,” Walker says. “It’s the responsibility of the vendor to have test data and your responsibility as a buyer to ask for it.”

Claxton takes this advice one step further. He likes to see for himself how these materials perform before recommending any to hydroseeding contractors.

One test involved a residential subdivision near Washington, D.C., where the top-soil at two sites had been removed. The two quarter-acre sites were just several hundred feet apart. Both sites were hydroseeded in late spring on the same day with a mix of 90 percent improved tall fescue and 10 percent improved perennial ryegrass, a 19-19-19 commercial grade fertilizer with micronutrients and a 70-percent wood and 30-percent paper mulch. A total of 2,400 pounds of mulch was applied at the first site and 4,000 pounds at the second site. Unlike the second site, 1.25 pounds of ProPlus NeutraLime Liquid and six pounds of JumpStart 5, both from Profile Products, were applied with the hydroseeding slurry at the first site. Ten days after seeding, both sites received 2.5 in. of rain.

The liquid lime-growth stimulant helps improve soil pH in the seed germination zone within seven to ten days after application. Since this project, another soil amendment has been introduced that is designed to balance pH faster and for a longer period – up to 18 weeks.

Claxton takes this advice one step further. He likes to see for himself how these materials perform before recommending any to hydroseeding contractors.

JumpStart 5 contains a package of growth stimulants, including seaweed extract, humic acid, endomycorrhizae, plus biostimulants and soil bacteria that increase root mass and top growth. It improves transfer of nutrients from the soil to the plant and helps break up clay and compacted soils to improve root penetration. It also includes a super-absorbent co-polymer gel (polyacrylamide or PAM) that enhances the water-holding capacity of the soil.

The liquid lime-growth stimulant treatment produced a consistently thicker stand of turf throughout the trial. “The difference between the two sites was still obvious six months later,” Claxton says. “The treated lawn responded better to heat stress during the summer and, when temperatures cooled in the fall, the turf recovered faster.”

He notes some economic benefits of the growth stimulating amendment. “Usually, it allows you to reduce fertilizer rates and costs because it enables plants to use fertilizer more efficiently,” Claxton says. “Also, as this test demonstrated, because this amendment increases the ability of soil to hold moisture, you can reduce the amount of mulch needed to protect the seed.”

While no one said growing grass and other vegetation in difficult conditions was easy, the right soil conditioner can give you an edge when it comes to making the site green with vegetation while putting more green money in your pocket.

For more information, contact Greg Northcutt, Northcutt Communications, Inc., 9330 Phillips Rd. SE, Port Orchard, WA 98366, (360)895-1887, fax (360)895-3213, e-mail: gregnorthcutt@att.net.

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