Nursery and Field Establishment Techniques to Improve Seedling
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New Forests 22: 75–96, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. Nursery and field establishment techniques to improve seedling growth of three Costa Rican hardwoods KEVYN ELIZABETH WIGHTMAN1, TED SHEAR1, BARRY GOLDFARB1 and JEREMY HAGGAR2 1North Carolina State University, Department of Forestry, Raleigh, NC, USA (E-mail: [email protected]); 2Organization for Tropical Studies, San Pedro, Costa Rica Accepted 11 August 2000 Key words: Calophyllum brasiliense, compost, Cordia alliodora, fertilization, herbicide, Hyeronima alchorneoides, native species, reforestation, root trainers, weed control Abstract. Seedlings of three economically important and ecologically different native hard- woods, Cordia alliodora (Boraginaceae), Hyeronima alchorneoides (Euphorbiaceae), and Calophyllum brasiliense (Clusiaceae), were grown in Rootrainers (a book-type container), paper pots, and plastic bags filled with either soil, soil with fertilizer, or compost substrates. After transplanting in the field, treatments with and without fertilizer and herbicide were applied to all nursery stock types. In the nursery, species responded primarily to substrate type. Cordia grew better in bags of soil with NPK fertilizer and compost than in unamended soil, probably responding to higher nitrogen availability. Despite large treatment differences at planting, there were no significant differences in plant size after one year in the field between book containers and bags. The exception were stump plants that were shorter and had higher mortality. Hyeronima grew better in compost than in soil with or without fertilizer, probably responding to higher phosphorus availability and lower bulk density of the compost. Plants produced in compost were also bigger after one year’s field growth. Plants produced with soil or in paper pots had higher mortality. Calophyllum grew less in compost compared to soil and grew better when micronutrients were added to the compost and soil. In the field, seedling produced in soil or with micronutrients had higher survival or growth, respectively. In general, species grew better with herbicide and fertilizer application after transplanting. However, there were no interactions with nursery treatments. Responses to field treatments were independent and thus additive to the nursery treatments. Differences in species response can be related to biomass allocation patterns and ecology of the species. Introduction Reforestation in Latin America is an increasingly popular activity due to the abandonment of unproductive cattle pastures and government incentive programs that support tree planting (Schelhas et al. 1997). To promote use of native species in forestry plantations and increase profitability for farmers in the Atlantic Lowlands of Costa Rica, species screening and provenance trials 76 for reforestation were established (Butterfield 1993, 1995; Butterfield and Fisher 1994). Currently, farmers in this region are almost exclusively planting native species used for furniture and construction wood because of their demonstrated fast growth and good form. Rotation periods of 15 years or less with one commercial thinning can be achieved. In Costa Rica, small holder farmers are the primary commercial reforesters, but the seedlings they obtain from community nurseries are often of poor quality. While research efforts often focus on identification of appropriate genotypes for reforestation, more attention needs to be given to seedling quality. Despite the enormous diversity of tropical tree species, the majority of non-industrial seedlings are produced in the same way, using 500–1500 cm3 perforated plastic (poly) bags with soil. The soil often contains high propor- tions of clay, has poor structure, and is low in plant nutrients. Generally little or no organic matter is incorporated. Due to poor substrates, plant growth is slow, extending into two nursery seasons, raising costs for the nursery, and inevitably reducing plant growth in the field. Plastic bags are used because they are inexpensive and readily available. They can cause root coiling, the spiral growth of roots along the smooth sides and bottom of the bag; this root deformation can cause toppling or basal sweep several years after planting, thus greatly lowering the value of the plantation (Mason 1985; Liegel and Venator 1987; Sharma 1987; Josiah and Jones 1992). Stumps plants (psuedoestacas) are an additional stock type produced in bareroot beds. They are derived from trees usually over 1.5 m tall by trim- ming major portions of the stem and root system (ideally 10 cm shoot and 15 cm root remain) after lifting. They are used for several species including Tectona grandis, Gmelina arborea, Bombacopsis quinata (Lamprecht 1986), and Cordia alliodora in the Atlantic lowland region of Costa Rica (Maroto, pers. comm.). They are popular because they require little maintenance in the nursery and are easy for landowners to transport. Limitations to seedling growth on abandoned pastures or agriculture fields in Latin America include weed competition, soil compaction and low fertility soils. Weed growth is persistent throughout the year due to favorable environ- mental conditions. Manual weeding with a machete is the most common vegetation control in plantations and weeding frequency depends on the cost and availability of labor (Rheingans 1996). Herbicides and fertilizers are used by the few landowners who have sufficient economic resources and are more commonly used in agriculture than in forestry. Early establishment is important for smallholder landowners in order to reduce weeding costs and possibly reduce time to harvesst. Early plant growth is regulated by the conditions at the planting site, and by the degree to which a plant’s phenotypic characteristics are adapted to a planting site (Burdett et al. 77 1983). High quality seedlings show substantial height growth the first year of planting, thus expressing their full genetic potential (Rose et al. 1990). They capture the site quicker, therefore allowing fuller expression of site poten- tial (Fry and Poole 1980). In contrast, use of poor planting stock can lower plantation survival and growth, increase site maintenance costs, and reduce confidence in reforestation. The use of the most appropriate planting stock can help overcome site limitations, while early and intensive site management can also accelerate seedling growth (Ladrach 1992). Increasing investment in nursery stock relative to investment in site preparation can increase financial returns on overall reforestation investments (South et al. 1993). In order to capitalize on advances made in reforestation with native species, seedling production techniques should be improved. Assessing outplanting performance must be an integral part of defining and adjusting target seedling characteristics. The objective of this research was to determine, for three widely planted tropical species with contrasting ecolog- ical characteristics, how different substrates, container types, and container volumes affect seedling growth in the nursery and early growth in the field. Weed control and fertilization were also tested to determine if nursery and field techniques could be integrated to improve seedling growth during establishment. Materials and methods The nursery was located at the La Selva Biological Research Station of the Organization for Tropical Studies (OTS) in the Atlantic Lowlands of Costa Rica (10◦26 N, 86◦59 W). The average annual rainfall and temperature are 3900 mm and 24 ◦C, respectively, and elevation averages 40 m amsl (McDade et al. 1994). Three rapidly growing native hardwood species that are found throughout the neotropics and are commonly planted in the Sarapiquí canton were studied. Cordia alliodora (R.P.) Cham. (Boraginaceae) is an early succes- sional species occurring on fertile soils; Hyeronima alchorneoides Fr. Allemao (Euphorbiaceae) is a late successional, canopy emergent species found on old alluvial soils; Calophyllum brasiliense Cambess (Clusiaceae) is an old growth, mid-canopy species found on residual soils (Ultisols). Nursery study For each species, 11 treatments were replicated in four randomized complete blocks. Treatments were: large (170 cm3) and small (85 cm3) Rootrainers with two composts; 500 cm3 bags (10×15 cm) with soil and NPK fertilizer, 78 Table 1. Substrate properties for nursery media. Bulk density CEC (meq/ P K Ca Mg Treatment pH (g/cm3) 100 cm3) (ppm) (ppm) (ppm) (ppm) Soil 5.7 0.99 14 67 338 1,680 40 Soil with NPK fertilizer 5.2 1.02 15 559 934 1,520 44 ∗ Compost A 7.2 0.45 53 1,935 8,392 420 120 ∗ Compost B 6.5 0.64 75 1,229 12,887 420 243 50% soil with 50% compost A 6.9 0.79 43 973 4,715 446 103 50% soil with 50% compost B 6.3 0.88 36 338 5,247 252 113 CEC = Cation Exchange Capacity ∗ with sulfur, 1 g/l 50% compost with 50% soil, 100% compost, or unamended soil; paper pots with two composts; and 250 cm3 bags with compost. Seeds were collected from phenotypically superior trees previously identified by OTS and each block contained seed from a single mother tree. Seed was directly sown in the containers between April and June 1995, depending on species. Each replicate of each treatment contained 30 plants: 20 for outplanting, 5 for destructive harvesting, and 5 for culling. From the three species combined, 660 trees were destructively harvested and 2,640 trees were planted. An alluvial soil was used in this experiment. For the fertilizer treatment, 10 grams of 10-30-10 N-P2O5-K2O fertilizer were incorporated into each bag of soil before sowing the seed. Compost A, commercially sold for seedling and vegetable production, was a mixture of 50% coconut husk fiber, 25% chicken manure (containing lime to control flies), 15% sugar cane bagasse and 10% charcoal. Compost B was a mixture of two composted fodder grasses, Pennis- etum purpureum (2 cultivars) and Axonopus scoparius. The pH of compost A was 7.7 and of compost B was 7.4, which are considered high for producing hardwood seedlings (van den Driessche 1984a). Elemental sulfur powder was added at 1 g/l to reduce the pH to 7.2 for compost A and 6.5 for B. When composts were mixed with soil, no sulfur was added.