EB1874

FERTILIZING EASTERN WASHINGTON CONIFEROUS FORESTS A Guide for Nonindustrial Private Forest Landowners * by James A. Moore, Donald P. Hanley, H.N. Chappell, John Shumway, Steven B. Webster, and John M. Mandzak

* A companion publication for western Washington forests: Fertilizing Coastal Douglas-Fir Forests: A Guide for Nonindustrial Private Forest Landowners in Western Washington, D. Hanley, H.N. Chappell, and E. Nadelhoffer, EB1800, WSU Cooperative Extension.

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BLANK PAGE Table of Contents begins on page 3.

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Table of Contents

Preface .................................................................................................... 5 Introduction ........................................................................................... 7 Basic Biology of Forest Fertilization ....................................................... 8 Before You Fertilize—Evaluate Your Stands ............................................ 8 Species ................................................................................................................ 8 Stocking .............................................................................................................. 8 Site Quality ......................................................................................................... 9

What Stands to Fertilize? ...................................................................... 10 Forest Health .................................................................................................... 10 Stand Age ......................................................................................................... 10 Micronutrient Research is Continuing .............................................................. 13

How to Fertilize Your Forest ................................................................. 13 Fertilizer Blends ................................................................................................ 13

Application Rates ................................................................................. 14 Application Methods ........................................................................................ 14 Safety ................................................................................................................ 14 Application Timing ........................................................................................... 14 Application Frequency ...................................................................................... 14 Fertilizer Costs .................................................................................................. 15

Increased Yields .................................................................................... 16 Biological and Economic Responses ..................................................... 16 Stands with High Response Potential ................................................................ 16 Stands with Medium Response Potential ........................................................... 16 Stands with Low Response Potential ................................................................. 17 Meta-sedimentary Soil Parent Material ............................................................. 17

Cost Share Assistance ........................................................................... 17 Forest Practices Act Compliance........................................................... 18 Final Notes—Seek Advice ..................................................................... 18

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BLANK PAGE Text begins on page 5.

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FERTILIZING EASTERN WASHINGTON CONIFEROUS FORESTS A Guide for Nonindustrial Private Forest Landowners by James A. Moore, Donald P. Hanley, H.N. Chappell, John Shumway, Steven B. Webster, and John M. Mandzak

Preface Forest Fertilization in Future Forestry Planning by S. P. Gessel and R. B. Walker * The present controversy over forest land use resulting in the withdrawal of large areas from wood production has brought a new focus on the role of soil fertility in forest productivity. The limited areas that will be available for growth of our wood crops must produce more and on a sustained basis to meet our needs. This is especially true if the role of wood and wood products in the economy of the Northwest is going to continue its present importance. These concepts and trends are being recognized by a number of professional groups who are developing programs of sustained land produc-

tivity and who also appreciate the need for sustaining and enhancing productivity for all aspects of forest use. We do know that current and future forest productivity depends primarily on the health and vigor of the trees in a stand. A number of factors affect this health and vigor, but among the most important are those relating to nutrition of the trees. This fact has not always been recognized in forestry. A common belief for many years was that somehow nature supplied all essential elements for all trees, and the forest soil contributed very little.

*

The late Stan Gessel was an Emeritus Professor of Forestry, and Richard W. Walker is a Professor Emeritus in Botany, both at the University of Washington.

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productivity in many of our Washington forest soils. From the research we also know many facts about the nitrogen cycle in forest soils, especially what cultural activities add or detract from the overall supply and how to increase nitrogen in both the short term and the long term. We also can detect deficiencies of other essential elements and supply these with relative ease to most forest areas. The most obvious way to improve nitrogen or other essential elemental supplies in forest soils is through direct application of necessary elements, or forest fertilization. You can purchase the essential elements in a variety of forms, either individually or in combination. Forest managers have commonly applied nitrogen to many forest areas in the Northwest in the form of urea, either by air or hand application. Other forms of nitrogen are available for fertilization programs, including processed sewage and other waste sludges, now called “biosolids.” These materials have generally demonstrated very good effects on the trees. Under present technology these biosolids are relatively high in cost unless the landowner is able to establish a cooperative program with the producer. A number of cooperative programs are in operation. The remainder of the bulletin will cover the detailed questions that must be considered in any forest level fertilization program. The authors hope to develop interest in the potential and opportunities of fertilization for small land owners to consider. WSU Cooperative Extension can provide more information.

Ezra Meeker, an early agriculturist in the Puyallup Valley, made it more specific by observing that when a tree burned he could hold all the ashes in his hands. This, he said, proved that trees had very low requirements and, therefore, no problems. Of course he did not know that some of the essential elements, such as nitrogen, are lost in the burning process and don’t remain in the ashes. Nor did he understand the importance of some of the necessary microelements. Fortunately, we now have years of research results that clearly establish the role of essential elements in tree growth and forest productivity. We know that forest soil nutrient management is an important part of both current and continuous, or sustained, forest productivity. We also have abundant research results showing that forest fertilization is a biologically sound and economically effective way of improving productivity. From this same research we also know the tissue levels and growth characteristics of trees that indicate either deficient or adequate amounts of the essential elements. These are detailed in a recent University of Washington College of Forest Resources Bulletin (Walker and Gessel, 1993).* The tissue levels can be estimated through color or growth characteristics, or determined exactly through chemical analysis. We also know something about the supply cycle of each essential element in our forest soil systems, and how this may be affected by our management practices. We know that nitrogen is likely to be the element that initially limits forest

*

Walker, Richard B. and Stanley P. Gessel, 1993, Mineral Deficiencies of Coastal Northwest Conifers. Institute of Forest Resources Contribution No. 70. University of Washington.

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not an “all or nothing” proposition. With proper planning, landowners can manage private forest lands for timber production and a variety of other objectives, including clean water, improved wildlife habitat, and recreational enjoyment. Forest fertilization is a way of maintaining or enhancing nutrients normally available to healthy stands of trees. It is not a remedy for critical nutrient deficiencies caused by poor management practices. Rather, forest fertilization is a way of supplementing a normal forest’s diet with nutrients to enhance growth. Conifer stands in the Inland Northwest usually are excellent candidates for fertilization. In fact, Pacific Northwest forest industries and agencies have long used forest fertilization to enhance the yield of both east- and westside second growth Douglas-fir. Forest fertilization is an integral part of the management regime planned for many conifer plantations established today. However, among nonindustrial private forest landowners, fertilization remains a largely underutilized practice. This bulletin emphasizes fertilization in eastern Washington conifer stands since many of those stands are likely to respond positively to the practice.

Introduction As a private landowner in the state of Washington, you presumably invest in your land for a variety of reasons. Conservation of wildlife habitat, wetland preservation, production of special forest products, income from the timber, personal enrichment, and recreation are a few of your potential management objectives. Increasing demand for timber and high stumpage prices are causing many private landowners to more seriously explore timber production as a financial option. Specifically, owners of second-growth conifer forests might find forest fertilization an excellent way to increase timber production, and provide improved wildlife habitat, improve general forest health, and increase financial return. Proper use of fertilization, along with other cultural techniques, such as thinning and pruning, can increase both the quality and quantity of wood grown in a normal rotation. Forest fertilization, however, is more than just a growth enhancing technique. Well-nourished trees are crucial to the health of forest ecosystems. Forest fertilization can improve wildlife habitat and aid in conservation goals. Finally, timber production is

Forest Fertilization Research in Inland Northwest Forests Forest Fertilization Research in Inland Northwest forests was initiated at the University of Idaho in the 1960s and began soon afterward in other organizations throughout the region. Early work demonstrated that nitrogen fertilization would increase Douglas-fir individual tree and whole stand growth. Promising results in early research projects and the initiation of operational fertilization programs were major factors influencing the formation of the Intermountain Forest Tree Nutrition Cooperative (IFTNC) which began in 1980 at the University of Idaho. Primary objectives of the IFTNC programs and other projects in the region were to provide forest managers with information on growth and response to nitrogen fertilization of second-growth stands of Douglas-fir and ponderosa pine. The IFTNC programs developed an extensive base of field installations. More recent activities focus on forest health relationships to nutrition, particularly the role of potassium (K). IFTNC members are interested in developing a better understanding of forest nutrition resulting in improved nutrient management of forests in the region.

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develop a deficient condition. Nitrogen deficiencies appear as a general “yellowing” of the needles. Nutrient deficiencies reduce growth. Applying fertilizer gives trees a “shot” of readily available nutrients. Nutrient deficiencies from nitrogen (N) usually reduce growth. Potassium (K) deficiencies render trees more susceptible to disease and insect attack. Higher tree mortality rates result. The most culpable organisms for this mortality are root rots and bark beetles. Usually, these are Armillaria and Phellinus root rots (Armillaria ostoyae and Phellinus weirii) and western and mountain pine beetles (Dendroctonus valens and Dendroctonus monticola).

Basic Biology of Forest Fertilization To understand the fundamentals of forest fertilization, it is helpful to first understand how a tree functions. Using water and nutrients obtained from tree roots and carbon dioxide from the air, chloroplasts in tree needles take energy from the sun to create sugars and oxygen. The sugars produce food energy for the tree. This food moves downward from the leaves to all living cells within the tree. Phloem, or inner bark, transports the food (sugar solution) from tree needles to the roots and other tissues. Eventually, phloem becomes bark as the tree grows. Cambium is a thin layer of specialized cells that divide to produce new phloem toward the outside of the tree and new sapwood toward the inside. Sapwood transports water and nutrients from the roots to the needles. The less active interior cells in the trunk gradually die and become heartwood. Heartwood is composed of dead cells that store water and nutrients and provide support for the tree. Roots absorb water and dissolved nutrients, such as nitrogen (N), potassium (K), and phosphorus (P). Roots also store sugar in the form of starch during tree dormancy. Important concepts to understand in forest fertilization are nutrient availability and the processes that alter it. Nutrient availability indicates the degree of usability by plants. For soils in eastern Washington, nitrogen is the element most commonly deficient; yet considerable nitrogen usually is present in the soil organic matter. It only becomes available to plants through the process of decomposition and mineralization. Mineralization is a natural process that converts organic forms of elements to inorganic forms trees can absorb through their roots. In the Pacific Northwest, cool temperatures slow decomposition and mineralization. During growth periods, trees often require more nitrogen than is available in the soil. When this occurs, trees

Before You Fertilize—Evaluate Your Stands Before you fertilize, evaluate your forest in the following five categories: species, stocking, overall forest health, stand age, and nutrient availability. Forest fertilization information provided here is for landowners growing coniferous forests established by planting or natural regeneration in eastern Washington.

Species Ponderosa pine, Douglas-fir, grand fir, lodgepole pine, and western larch have all demonstrated nitrogen growth responses. Western hemlock, western redcedar, Engelmann spruce, and western white pine are common associates. Less information is available for these latter species.

Stocking An accurate inventory is an excellent place to start when you are contemplating forest fertilization. Foresters call the inventory a cruise, and the process of inventorying is called forest cruising. Cruising helps you determine the kinds and amounts of wood occurring on a piece of land. Today, most people contract with consulting foresters to cruise their land, but this should not prevent you from conducting your own inventory. For a concise description on how to cruise your 8

forest, see PNW31, Measuring Trees, available from WSU Cooperative Extension. Properly thinned stands usually are the best candidates for fertilization. A well-stocked forest has an optimum number of trees per acre for ideal growth. Normal stocking rates, expressed as total square feet of basal area, vary depending on tree species and site quality. Do not fertilize a forest where excessive competition for sunlight has closed the canopy and trees are overcrowded. Trees should have sufficient space around them for crown expansion. Without crown expansion, stem diameter growth is greatly reduced.

factors, which would usually limit growth such as light and water, are abundant. Habitat Types are useful for ranking a stand’s potential for nitrogen fertilization in eastern Washington. A Habitat Type is a land classification based upon which tree species and understory shrubs are expected to dominate a site over time. This classification system suggests the biological potential of the site. Similar Habitat Types are grouped by series, such as the Ponderosa Pine (Pinus ponderosa) Series, the Douglas-fir (Pseudotsuga menziesii) Series, the Western Hemlock (Tsuga heterophylla) Series. (see figure 1). Table 1 ranks common Habitat Types of eastern Wash-

Larix lyallii

Pinus albicaulis

Abies lasiocarpa

Tsuga heterophylla

Thuja plicata

Pinus monticola

Abies grandis

Picea

Pinus contorta

Larix occidentalis

Pseudotsuga menziesii

Pinus ponderosa

Response to fertilization is greatest on sites where nutrient deficiencies limit growth, but other

Tsuga mertensiana

Site Quality

alpine tundra timberline h. t. s.

Tsuga mertensiana climax Abies lasiocarpa series Tsuga heterophylla series Thuja plicata series Abies grandis series Picea series

Pseudotsuga menziesii series Pinus ponderosa series grassland Figure 1. Arrows show the relative elevational range of each species; solid portion of the arrow indicates where a species is the potential climax and dashed portion shows where it is seral. Distribution of Forest Trees and Habitat Type Series as influenced by elevation and precipitation.*

*

Adapted from: (Pfister, Robert D., B.L. Kovalchik, S.F. Arno, and R.C. Presby. 1977. Forest Habitat Types of Montana. USDA For. Serv. Gen. Tech. Rep. INT-34.)

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aspect, elevation, and soil parent material. Most of these factors are integrated in the concept of Habitat Types. We recommend using Habitat Type series to identify stands for nitrogen fertilization. Nitrogen is the most common growth-limiting nutrient in stands. Response to nitrogen fertilization has been demonstrated in an extensive set of field trials in the inland Northwest. Geographic Subregions are used in conjunction with Habitat Type Series to determine high priority stands to fertilize in eastern Washington. After considering Geographic Subregion and Habitat Type series in deciding whether to apply nitrogen fertilizer, growers should also evaluate soil parent material. Use Table 1 (page 11) for this determination. Be sure to read the notes accompanying this table.

ington by geographic subregion and soil parent material* for their potential response to nitrogen fertilization.

What Stands to Fertilize? What stands to fertilize? Foliage and soil analyses have not proven practical as stand selection techniques in eastern Washington. Foliar analysis serves as a site-specific tool for small acreages, usually less than an acre, unless the samples are systematically collected from your acreage. Microsite variability makes this analytical tool impractical for diverse, nonindustrial private forest ownerships. Site variability is influenced by slope, Pend Oreille Okanogan III

Forest Health

Ferry

Evaluation of the general health of the stand is also important. Fertilization is a method for maintaining and enhancing nutrient availability. You will get the best return on your money if you apply nitrogen fertilizer to trees that are already healthy. Avoid stands that are heavily infected with root rots such as laminated root rot (Phellinus weirii) and Armillaria (Armillaria ostoyae); trees with damaged roots normally will not respond to nitrogen fertilization treatments. Forest fertilization is a viable operation for forest stewardship purposes. Several larger industrial owners in eastern Washington have fertilized to improve general forest health. These actions may provide improvements in wildlife habitat for deer and elk as well as increase production of hard and soft mast that small rodents and birds use, respectively. Huckleberry production often is enhanced greatly, and forage production is improved.

IV Stevens

Chelan Douglas II

Lincoln

Spokane

Kittitas

Yakima I Klickitat

Figure 2. Geographic Subregions are used in conjunction with Habitat Type Series to determine high priority stands to fertilize in eastern Washington. Subregion I, South Cascades; Subregion II, Central Cascades; Subregion III, North Cascades; and Subregion IV, Northeast Washington (Source: Intermountain Tree Nutrition Cooperative, University of Idaho, Moscow, ID).

Stand Age In general, expect maximum growth response in young stands, since nutrient demand is highest at about the time of tree canopy closure. Fertiliza-

*

Soil Parent material can be determined from soil classification documents available from the Natural Resources Conservation Service (NRCS). NRCS offices are located in the USDA Service Center in most Washington counties.

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Table 1. Nitrogen Fertilization Response Potential by Geographic Subregion, Habitat Type, and Soil Rock Type (See notes on following page). This table refers to the Habitat Type of the site, which may not reflect the current tree species of the stand.

Habitat Type Series

Parent Material

South Cascades

Central Cascades

North Cascades

Northeast Washington

Douglas-fir Series

Basalt Granite MetaSedimentary (3) Sandstone Glacial

low (1) no data do not use N only no data no data

low no data do not use N only low no data

variable (2) low do not use N only variable low

low low do not use N only no data low

Grand fir Series

Basalt Granite MetaSedimentary Sandstone Glacial

low (1) no data do not use N only no data no data

medium no data do not use N only high (7) no data

not present (4) not present (4) not present (4) not present (4) not present (4)

medium medium (5) do not use N only no data variable (6)

Basalt Granite MetaSedimentary Sandstone Glacial

low (1) no data do not use N only no data no data

no data no data do not use N only very high (7) no data

no data no data do not use N only no data variable (6)

high high (5) do not use N only no data variable (6)

do not fertilize (8)

do not fertilize (8)

do not fertilize (8)

do not fertilize (8)

Cedar-Hemlock Series

Ponderosa pine Series

Notes to Table 1: Habitat Types found elsewhere in eastern Washington. Further, Douglas-fir Habitat Types below 3000 feet in the North Cascades Subregion respond more like Douglas-fir Habitat Types found elsewhere.

(1) The Wanapum basalt formation and olivine basalt formations common in this area show no response to nitrogen-only fertilization. Perhaps soils derived from these rocks are low in other nutrients such as sulfur, potassium, copper, and boron.

(3) Forests growing on meta-sedimentary rocks seem to have a variety of nutritional deficiencies and associated forest health problems. We do not

(2) Douglas-fir Habitat Types above approximately 3000 feet elevation respond more like grand fir 11

recommend fertilizing with nitrogen-only on these types of rocks, as they are likely also lacking potassium, sulfur, and perhaps micro-nutrients as well.

(6) Soils developed on mixed parent materials, primarily derived from glacial action, show variable nitrogen response, likely due to low potassium levels in the soil.

(4) Grand fir habitat series (or grand fir tree species) are not present in the North Cascades Subregion.

(7) Stands growing on soils derived from sandstone rocks in the Central Cascades and North Cascades subregions showed the most consistently high nitrogen response of all the different rock types studied in eastern Washington.

(5) In the North Cascades and Northeast Washington subregions, the darker granites in these areas showed medium response to nitrogen-only fertilization. However, whiter granites showed low nitrogen response in adjacent Idaho, likely due to low potassium levels in soils derived from these rocks.

(8) Ponderosa pine Habitat Types are usually too dry to show significant response to fertilization.

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tion at this stage of development provides an opportunity to achieve significant increases in growth rates and allows harvesting of a large number of stems of merchantable size in subsequent commercial thinning. If you do not remove increased stand growth by subsequent thinning, tree mortality will reduce the growth gains considerably over time. Commercial thinning allows harvesting of merchantable volumes as well as encouraging larger, healthier residual trees. Fertilize near the time of final harvest for two main reasons: first, money invested in fertilization is held for the shortest period of time before financial returns are realized. Second, the volume gain occurs on larger, high value trees, and can be captured in the final harvest.*

1) choosing a nitrogen, nitrogen-potassium (N-K), or micronutrient fertilizer blend, 2) application rates, 3) application methods, 4) application timing, and 5) how often to fertilize.

Fertilizer Blends Nitrogen is the element most commonly used as a fertilizer for second-growth coniferous forests. In all forest fertilizer applications, nitrogen should be applied. Nitrogen usually is applied as urea [CO(NH2)2]. Urea has 46% N content, higher than other nitrogen fertilizer formulations, which makes it more economical to apply. When potassium (potash) is necessary†, this element often is applied as KCl (potassium chloride) in a mixture with urea. Potassium in the form of KCl has 52% K content. Some industrial forest landowners use a micronutrient fertilizer blend (Option #3 in Table 2) to alleviate suspected microelement deficiencies.

How to Fertilize Your Forest In the following section, we address five steps involved in fertilizing forest stands:

Micronutrient Research is Continuing Initial research results from the Intermountain Forest Tree Nutrition Cooperative (IFTNC) indicate that micronutrients may be limiting for North Idaho forests. This discovery has led current IFTNC research efforts to determine if eastern Washington forests react similarly. Far more information is available on nitrogen response than for response to other nutrient elements. In some eastern Washington stands, deficiencies of potassium, sulfur, copper, boron, and other micronutrients are suspected as limiting growth and influencing forest health, especially the relationship to bark beetle and defoliator attacks (Mandzak and Moore, 1994).** Application of the macronutrient sulfur has shown positive results for tree growth and for Douglas-fir and grand fir root rot resistance on some sites in Idaho. Commonly these sites are basalt parent materials with a surface volcanic ash deposit. If you suspect that elements in addition to nitrogen are limiting, review information about forest soils parent materials before making a potassium fertilizer decision.

*

In larger, well regulated forests, young stand fertilization can increase the cut allowable from older trees where a relatively even flow of timber is desired. † If the soil parent material for the candidate stand is Meta-Sedimentary, we recommend a nitrogen-potassium fertilizer blend. Current research is underway to determine if potassium should be used on other parent material types in eastern Washington. ** Mandzak, John M., J. A. Moore, 1994. The Role of Nutrition in the Health of Inland Western Forests. Pp. 191-210 in Journal of Sustainable Forestry, Vol. 2, Part 1. Haworth Press Inc.

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Research is ongoing in this area; however response data are currently lacking for most soil parent materials. Many land managers justify this more expensive fertilizer option because they believe it will be beneficial over the long term.

forest allow you access to all sections and that you are able to distribute the fertilizer evenly. Fertilizer can be spread by hand from a bucket or from a cyclone spreader. If your forest is large enough that only a helicopter operation is feasible, the more concentrated levels of nitrogen found in urea will translate into less air time and lower application cost per acre.†

Application Rates We suggest you choose one of the three recommended fertilizer blends listed in Table 2.

Safety When distributed uniformly in the proper amounts, fertilizer does not pose a threat to wildlife or livestock. However, you should strictly avoid having standing piles of fertilizer on the ground

Application Methods Distributing fertilizer by hand is possible, provided that the size, location, and terrain of your

Table 2. Operational Blended Fertilizer Choices for Eastern Washington

Nutrient

Elemental Rate (lb./ac)

Suggested Sources

Fertilizer Rate (lb./ac)

Option 1 Nitrogen Only

$ 73 200

Urea

435

Urea Potassium Chloride

435 333 768

Option 2 Nitrogen, plus Potassium Total Material

$ 117 200 N 170 K

Option 3 Nitrogen Potassium Sulfur Boron Copper Sulfur Total Material

Estimated Chemical Cost per Acre *

$ 200+ 128 N 170 K 90 S 76 N 5B 10 10

Urea Potassium Chloride Ammonium Sulfate

270 333 379

Borate FG Copper Sulfate

35 40 1057

* Estimated costs (January 1997) based on blended fertilizer purchased in 50-pound sacks. Prices reflect average price in eastern Washington. This price does not include application costs. †

According to Boise Cascade Corporation, application costs add $0.06/pound on large operations.

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(for example, as a result of a bag spill). At that level of concentration, nitrogen can be toxic to wildlife and domestic animals. Clean up spills immediately. Strictly prevent spills into water, since the concentrations can harm aquatic life.

Application Timing In the Pacific Northwest, apply the fertilizer mixture in the rainy season, during late fall, winter, or early spring. Optimal conditions are cool, wet, windless weather with temperatures of 55°F or cooler. Never apply nitrogen fertilizer in hot, dry, windy weather since volatilization can occur. In volatilization, fertilizer N is transformed into ammonia gas that dissipates into the atmosphere— not part of your investment strategy! Fertilizer can be applied by hand over snow without problems. It melts through the snow cover (up to 18") rapidly and dissolves into the soil. We do not recommend aerial applications over snowcovered tree canopies. Nitrogen fertilizer applied in this way may not reach the forest floor and may be lost to the system. We also do not recommend applying fertilizer on bare frozen ground. This inhibits movement of the chemicals into the soil profile and increases the likelihood that the fertilizer will migrate to streams and lakes.

Fertilizer Costs Chemicals for large fertilization projects are typically delivered in railroad car lots then trucked to heliports near the stands to be fertilized. For smaller projects of a stand or two, fertilizer may be purchased directly from agricultural supply stores. In fall 1996, farm store price for urea (46-0-0) was about $73/acre and for potassium chloride $117/ acre. These costs do not include application and chemical delivery expenses that may increase the final cost by 30% to 50%. Alternatively, aerial applicators may bid on the job to include the fertilizer cost (application + fertilizer). If you are considering aerial application this may be a beneficial alternative. The operator can take advantage of bulk unit prices. Fertilizer costs can vary, so you should consider the most cost-effective formulation. When ordering bagged fertilizer from the supplier, consider how you will handle the bags. Fertilizer can be custom packaged in 50-lb or 80-lb bags, if you will be hand loading or transporting the fertilizer. Fifty-pound bags are better for hand applications.

Application Frequency How often to apply fertilizers largely depends on the age of your stands and the length of the potential investment period. Response to a single nitrogen application can last up to 8 years on the Grand Fir Habitat Type Series and up to 5 years on Douglas-fir Habitat Type Series. Plan intermediate harvests (commercial thinning) to regulate tree density and capture the growth increases from fertilization. In theory, smaller, more frequent fertilization treatments will provide the best response, although fertilization logistics usually conspire against this. As an example, after a stand has been treated for the first time, lighter applications on perhaps a 5year cycle may be best. Contact a specialist for detailed recommendations.

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These follow: • Amount of extra wood fertilizer will add to the stand, • Economic value of the extra wood, and • Probability of achieving an economically acceptable response.

Increased Yields By fertilizing second-growth conifer stands with nitrogen, you may increase stand growth by about 25% for an 8- to 10-year period. Done in conjunction with other cultural techniques like thinning and pruning, the yield and value effect of fertilization can be even more dramatic. It is important, however, to factor in losses from such things as pests, disease, competition, and weather. An increase in merchantable stand volume can be translated into a similar increase in the money received at harvest, minus all fertilization expenses. For the Grand Fir Habitat Type Series, which are generally better sites, cumulative growth response for Douglas-fir produces approximately 350 cubic feet/acre or more growth in the 8-year period. Douglas-fir growing on Douglas-fir Series Habitats result in only 125 cubic feet/acre for the 8-year period.

Two readily available site characteristics, habitat series and soil parent material, provide a simple means of grouping stands into high, medium, and low response potential.

Stands with High Response Potential Eastern Washington Douglas-fir stands with high potential response produce between 1200 and 2200 board feet per acre of extra wood in a 10-year period following the application of 200 lbs/acre of nitrogen. Return on investment* in these stands ranges from about 15% to slightly over 20%.† Stands that are predominantly Douglas-fir growing on: 1) Grand Fir Habitat Type Series on basalt and sedimentary parent materials, or 2) Cedar Habitat Type Series and basalt parent materials, or 3) Douglas-fir Habitat Type Series on glacial parent material in the North Cascades Subregion all fit within the high response potential shown in Table 3. An exception to this classification occurs in stands in the Grand Fir Habitat Type Series on Wanapum Basalt in the South Cascades. Response to nitrogen has been consistently low on these basalt flows, which should not be considered for nitrogen fertilizer additions. Research is underway to determine whether response can be obtained with multi-nutrient fertilizers.

Biological and Economic Responses Stand response to 200 lbs of nitrogen as Urea varies widely in eastern Washington. In some cases nitrogen fertilizer increases growth by more than 2000 board feet per acre in 10 years. In a few instances the addition of nitrogen actually reduces stand growth. Region-wide averages are of little practical use to woodland owners interested in applying nitrogen or multi-nutrient fertilizer. Owners are interested in how well their specific stands will respond to nitrogen additions. In determining whether to apply fertilizer to a stand, three key pieces of information are needed.

Stands with Medium Response Potential Stands in this class respond between 750 and 1100 board feet per acre over 10 years and produce

* Return on investment is the interest rate earned on the fertilizer investment. For example, suppose you fertilize one acre of forest land today for $100 and 10 years later you harvested an extra 1000 board feet at $300 per thousand board feet. This would represent a before tax return on investment of 11.6%. †

Five assumptions are needed to calculate return on investment: 1) Harvest of the additional volume grown 10 years after fertilization; 2) Stumpage price of $300 per thousand board feet; 3) a board foot-cubic foot ratio of 4 to 1; 4) a discount rate of 6%; 5) fertilizer costs of $100/ acre including application costs.

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a return on investment ranging from 8% to 13%. Between 50% and 85% of the stands fertilized with nitrogen respond by more than 600 board feet /acre. Stands in Grand Fir Habitat Type Series on granite or glacial parent material and stands found in the Cedar Habitat Type Series on glacial deposits fit within the medium response potential class (Table 1).

pected results. Unfertilized stands in this grouping consistently had higher than expected mortality. The primary agents were disease, breakage, and insects. Nitrogen fertilizer applied at 200 lbs/acre N reduced mortality substantially. However, with higher rates of N fertilization mortality was similar to that on unfertilized stands. It is unclear why stands on meta-sedimentary parent material have higher mortality, or how lower doses of nitrogen fertilizer reduce these effects. We do not know whether mortality will continue at a reduced level or increase after the effects of N fertilization are gone. Until research provides additional information, landowners adding nitrogen to stands on meta-sedimentary parent materials should anticipate a low response potential. Research is continuing in these low productivity stands.

Stands with Low Response Potential Stands in this class usually respond by less than 700 board feet/per acre in a 10-year period and occasionally nitrogen fertilizer results in reduced growth. Return on investment is usually less than 6%, and on average less than 40% of the stands respond by more than 600 board feet/acre after 10 years. Include in this class: 1) all stands growing in Douglas-fir Habitat Type Series except for those found on glacial parent materials in the North Cascades Subregion, and 2) all stands growing on meta-sedimentary parent materials, and stands growing on Wanapum Basalt. Research is continuing in these low productivity stands.

Cost Share Assistance Cost share programs are available for nonindustrial private forest landowners who pursue intermediate silvicultural treatments such as thinning, pruning, and fertilization. Forest fertilization operations may be eligible for USDA cost-sharing funds. These funds typically reimburse landowners

Meta-sedimentary Soil Parent Material Stands growing in the Grand Fir Habitat Type Series on meta sediments provided some unex-

Table 3. Generalized Responses for Fertilizing Coniferous Stands Using One Application of Nitrogen Fertilizer (200# N per Acre) Grand fir HT Series

Cedar HT Series

Priority

Priority

Priority

Granite

Low

Medium

No data

Basalt

Low

High

High

Meta-sedimentary

Low

Low

Low

Sedimentary

Low

High

No data

Glacial

Low

Medium

Low

Rock Type

Douglas-fir HT Series

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near running or open bodies of water. The sizes of required buffer zones vary according to the types of water on your property. For a Forest Practices Application and clarification of the regulations, consult a Forest Practices Forester with the Washington Department of Natural Resources (1-800527-3305), prior to application.

for 65% to 75% of costs. Local offices of the USDA Consolidated Farm Service Agency (CFSA—formerly ASCS) or your state forestry agency, the Department of Natural Resources (DNR), can advise you regarding the eligibility and requirements in your area. To qualify for USDA cost-sharing funds, landowners must apply and receive written approval from the CFSA before work begins.

Final Notes—Seek Advice

Forest Practices Act Compliance

Fertilization can be a powerful management tool. It can increase yields and improve forest health of second growth coniferous forests. When fertilization is used in conjunction with thinning and pruning, increase in timber yield and value can be substantial. Accurate information is the foundation of good decisions. The more you know about your forest and growing trees for timber, the better. Before committing to a forest management plan that includes fertilization, seek the advice of a professional consulting forester. Ask about qualifications concerning fertilization before hiring anyone. Consulting foresters working in the state are listed in WSU EB1303, Consulting Foresters Directory for Washington Landowners.

Forest fertilization is regulated by the Washington State Forest Practices Act. The law requires hand application in riparian and wetland management zones unless the Washington Department of Natural Resources (DNR) has approved a site specific plan for another method. Aerial application requirements are varied. In general, avoid application to water or wetlands. Buffers are required around all waters, residences, and adjacent agricultural land. While water nitrate levels after fertilization operations have never reached levels that pose a concern for human health, concerns exist for fish eggs and fry and other aquatic life. Be scrupulously careful whenever you are dealing with fertilizers

Publication by: James A. Moore, Ph.D., Professor of Forest Resources, Director of Intermountain Tree Nutrition Cooperative, University of Idaho, Moscow, ID; Donald P. Hanley, Ph.D., Washington State University Cooperative Extension Forester, Seattle; H. N. Chappell, Ph.D., Forest Nutrition Director, Potlatch Corporation, Warren, AR, and formerly Research Professor and Director, Stand Management Cooperative, University of Washington; John Shumway, Ph.D., Natural Resource Scientist, Washington Department of Natural Resources, Olympia; Steven B. Webster, Ph.D., Area Extension Forester, WSU Cooperative Extension, Lewis County; and John M. Mandzak, Ph.D., Principal Silviculturist, Boise Cascade Corporation, Boise, ID. Photographs courtesy of Robert Gonyea, University of Washington Stand Management Cooperative, Seattle. 18

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COOPERATIVE EXTENSION

College of Agriculture and Home Economics WSU Cooperative Extension bulletins contain material written and produced for public distribution. You may reprint written material, provided you do not use it to endorse a commercial product. Alternate formats of our educational materials are available upon request for persons with disabilities. Please contact the Information Department, College of Agriculture and Home Economics, Washington State University for more information. You may order copies of this and other publications from the WSU Bulletin office, 1-800-723-1763, or online http:// caheinfo.wsu.edu Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may be reported through your local Cooperative Extension office. Trade names have been used to simplify information; no endorsement is intended. Published August 1998. B. Subject code 400. EB1874

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