XIV WORLD FORESTRY CONGRESS, Durban, South Africa, 7-11 September 2015
Hybrid poplar: a potential multipurpose tree for drip irrigation in semi-arid temperate regions Michael K. O’Neill1*, Samuel C. Allen1, Robert F. Heyduck2, Kevin A. Lombard1, Dan Smeal1 and Richard N. Arnold1 New Mexico State University Agricultural Science Center, P.O. Box 1018, Farmington, NM 87499 USA; NMSU Alcalde Sustainable Agriculture Science Center, Alcade, NM, USA. * Author for correspondence: Dr. Michael K. O’Neill, Phone: +1-505-960-7757, Email:
[email protected] 1 2
Abstract Establishment of plantations in the American Southwest has lagged behind other regions of the US due to water scarcity and poor-quality soils. With limited water available for irrigation, there is interest in drip-irrigated plantations that can provide biomass, biofuels, other wood products, and environmental services from short rotation woody crops. Given the success of hybrid poplar (Populus spp.) plantations in semi-arid Eastern Oregon, the New Mexico State University Agricultural Science Center at Farmington, NM began research with drip-irrigated hybrid poplar in 2002, initially with a provenance trial of 10 clones obtained from nurseries in the Pacific Northwest. Based on the success of P. canadensis (a P. deltoides x P. nigra cross), a new test was established in 2007 to study its growth under varying irrigation amounts. Four clones (433, 544, 910 and 911) were planted in replicates in a 3.6 x 3.6 m-grid spacing (770 stems ha-1) in April 2007, and drip irrigated at four target levels (70, 80, 120 and 130%) of crop evapotranspiration (ETc). Total ETc at 100% replacement for 2007-2012 was calculated at 6.3 m; actual applications (including 0.4 m of rainfall) for the respective treatments averaged 4.5, 4.9, 6.2 and 6.7 m, reflecting challenges posed by water pressure and maintenance issues. Tree growth was similar and highest for the 120 and 130% target irrigation levels. Average wood volume (WV) for these two treatments was 145 m3 ha-1 and average biomass was 115 Mg ha-1. Across clones, entry 433 led for height at 15.5 m and WV at 132 m3 ha-1, followed by clone 544. Both clones had similar diameters at breast height (19.5 cm) and biomass (~103 Mg ha-1). Average water use efficiency over all irrigation treatments was 1.89 and 1.78 kg m-3 for clones 433 and 544, respectively, followed by clones 910 and 911 at 1.57 kg m-3. This study highlights the silvicultural adaptability and promising growth of drip-irrigated hybrid poplar in a semi-arid temperate region. Keywords: Biomass, Populus, SRWC, temperate drylands, water use efficiency
Introduction, scope and main objectives Production of trees for woody biomass and environmental services is challenging in semi-arid areas due to the slow growth rate of many tree species combined with the often marginal soils in which they are grown. The problem is frequently compounded by the limited water available for irrigation, as is the case in much of the American Southwest. Given the interest in hybrid poplar (Populus spp.) in other parts of North America as well as in many other countries, the opportunity to study poplar growth and adaptability in a semi-arid temperate setting is intriguing. Hybrid poplar is one of the fastest-growing temperate trees, capable of producing merchantable products and woody biomass in
2 rotations of 3-15 years, as well as environmental benefits such as carbon sequestration, windbreaks, and wildlife habitat. It is also tolerant of various soil types and pH levels. The New Mexico State University Agricultural Science Center at Farmington, NM, USA, began research with drip-irrigated hybrid poplar in 2002, initially with a provenance trial of 10 clones obtained from nurseries in the Pacific Northwest. This work was undertaken in part to address agricultural improvement and market development issues of the center’s target communities, including the Navajo Agricultural Products Industry (NAPI), a large 35,000-hectare commercial farm operation administered by the Navajo Nation, an indigenous sovereign governmental entity within which the center is located. Based on the center’s success with P. canadensis (a P. deltoides x P. nigra cross), a new test was established in 2007 to study its growth under varying irrigation application rates. The research objectives of this new study were: 1) to identify the most suitable clonal material for drip irrigation on high pH soils in a semi-arid environment, and 2) to develop an appropriate irrigation regime for this setting in terms of amount of water, frequency and seasonal duration based on crop evapotranspiration (ETc) replacement levels. Methodology/approach The trial was established in the spring of 2007 using 4 hybrid clones (entry nos. 433, 544, 910 and 911) (all Populus deltoides x P. nigra crosses) that had been among the leading producers in earlier studies at the center. Clones were planted in replicates in a 3.6 x 3.6 m-grid spacing (770 stems ha-1) in April 2007, and drip irrigated from 2007-2012 during the growing season at four target levels (70, 80, 120 and 130%) of crop evapotranspiration. Prior to planting, the field was disked and levelled, and a pre-emergent herbicide was applied. Netafim Ram pressure-compensating surface drip lines with four emitter sizes (2.0, 2.3, 3.5 and 3.8 L/hr; emitters every 0.9 m) were installed with one line per row of trees. A whole-plot was set up as four 117-m long, 3.7-m wide rows of a single emitter size (or irrigation level) across which four split-plots (comprised of the four clones, randomly assigned) were superimposed with plots comprised of a 4 x 8 stem planting rate. Irrigation treatments and clone entries were replicated in four blocks for a total of 2,048 trees across 2.75 ha. Northwestern New Mexico is characterized as a high desert, semi-arid region (due to a rain shadow effect) with an elevation often exceeding 1,700 m and a mean annual precipitation of 205 mm (Lombard et al. 2013; Smeal et al. 2014). Average monthly temperatures range from -1.1 °C in January to 24.3 °C in July. The soil at the experimental site was originally classified as a Kinnear sandy loan (fine-loamy, mixed, calcareous mesic Typic Camborthid) (Anderson 1970) and later reclassified as a Doak sandy loam (fine-loamy, mixed, mesic Typic Haplargid) (Keetch 1980). Water holding capacity in a 1-m profile is 13.8 cm and pH averages 8.2, resulting in a moderately calcareous soil. At high soil pH, iron availability is reduced, resulting in possible leaf chlorosis issues (Brady and Weil 1999; Havlin et al. 1999). Although poplar consumptive-use estimates were not available in the Farmington area, monthly water-use rates of first, second, and third season poplars grown at a site with similar climatic conditions in east-central Oregon (USA) were reported by Gochis and Cuenca (2000). These values were used to generate crop coefficients relating to each year of poplar growth and to growing degree days (GDD). The crop coefficients then modify the Penman-Monteith Evapotranspiration value for a given day (ETTALL) and these values are used to program irrigation. The output ETc replacement value was then further modified by multiplying by the respective treatment levels: 70, 80, 120 or 130%. This was accomplished in practice by running all units for the same time period each day, while the differential irrigation levels were maintained by the differing emitter sizes. Irrigation was started in April/May of each year and ran through late September/early October (the practicable frost-free growing season at the site), and was programmed as prescribed by calculated ETc demand. Liquid nitrogen fertilizer and micronutrients were applied via the irrigation system. Tree growth data were
3 collected later each year during the dormant season. Wood volume for each study tree was determined after Browne (1962) and scaled to a hectare basis, and biomass was calculated on a hectare basis (Jenkins 2003). Water use efficiency was expressed as the relationship of total water inputs (m) to final biomass (kg m-3). Data were analyzed using the CoStat ANOVA procedure with mean separation by Fisher’s LSD (CoHort 2008).
Results Results for the 2007-2012 study period are presented in Table 1 below and show overall growth characteristics and water use efficiencies for the four irrigation levels and clonal entries. For irrigation level, six-year growth was similar and highest for the 120 and 130% target levels for all measured parameters. Average diameter at breast height (DBH) for these two levels was 20.6 cm, average height (Ht) was 16.0 m, average wood volume (WV) was 145.3 m3 ha-1, and average total aboveground biomass (TAB) was 115.4 Mg ha-1. Examining across clones, entry 433 led for height at 15.5 m and WV at 131.6 m3 ha-1, followed by clone 544. Both clones had statistically similar DBH (19.5 cm) and TAB (102.5 Mg ha-1), and were larger and more productive than the other two clonal entries. Total crop evapotranspiration (ETc) at 100% replacement for the six-year study period was calculated at 6.3 m; actual applications (including 0.4 m total rainfall) for the respective treatments averaged 4.5, 4.9, 6.2 and 6.7 m, reflecting challenges posed by water pressure and maintenance issues. Average water use efficiency (WUE) for irrigation levels 3 and 4 was 1.9 and 1.7 kg m-3, respectively, and average WUE for clones 433 and 544 was 1.9 and 1.8 kg m-3, respectively, indicating best overall performance from these target irrigation levels and clonal entries.
Table 1: Growth characteristics and water use efficiencies of four hybrid poplar clones (Populus deltoides x P. nigra) grown under four irrigation levels from 2007 to 2012. NMSU Agricultural Science Center at Farmington, New Mexico, USA. 2012.
Irrigation Level* or Clone
DBH** (cm)
Height (m)
1
16.8 C†
12.7 C
2
17.7 B
13.6 B
3
20.7 A
15.6 A
Wood Volume (m3/ha)
Total Aboveground Biomass (Mg/ha)
Cumulative Irrigation + Rainfall (m)
Water Use Efficiency (kg/m3)
71.2 B
4.5
1.6 B
91.3 B
80.1 B
4.9
1.6 B
142.1 A
116.2 A
6.2
1.9 A
78.0 C
4
20.4 A
16.3 A
148.4 A
114.5 A
6.7
1.7 A
433
19.5 a‡
15.5 a
131.6 a
104.9 a
5.6
1.9 a
544
19.4 a
14.8 b
119.6 b
100.1 a
5.6
1.8 a
910
18.4 b
13.9 c
104.8 c
88.5 b
5.6
1.6 b
911
18.4 b
14.1 c
105.6 c
88.4 b
5.6
1.6 b
19.0
14.6
115.8
95.5
5.6
1.7
Mean***
*Water applied equivalent to 1=70%, 2=80%, 3=120%, or 4=130% of replacement crop evapotranspiration (ETc) rate. **DBH = Tree diameter at breast height (1.37 m). ***Mean is the average of 4 treatments (irrigation factor or clone), each consisting of 4 replicated plots (12 trees/plot). †For irrigation level, means with the same uppercase letter are not significantly different at the 0.05 level of probability. ‡For clone, means with the same lowercase letter are not significantly different at the 0.05 level of probability.
4 In addition, the top-performing clone in the trial emerged as entry 433, commercially known as OP367, a cross originally developed in New York State in the early 1900s. This clone consistently showed good performance in all growth parameters over the duration of the trial. To delineate the effects of varying irrigation levels on a specific entry, OP-367 was examined individually in terms of DBH, height, wood volume and total aboveground biomass (Figure 1). Irrigation levels 3 and 4 (120% and 130% of ETc) generally resulted in the highest averages for these parameters, with irrigation level 3 suggestive as perhaps the most suitable level among the four treatments in terms of growth and water use efficiency, with no apparent benefit suggested (growth-wise, irrigation-wise, or cost-wise) from using a higher irrigation level. Additionally, the 120% target ETc level served as a practicable cushion for mitigating occasional irrigation shortfalls resulting from human and system error over the long duration of the study. This information is helpful in establishing upper/lower irrigation level thresholds in the development of best managements plans (BMPs) for hybrid poplar grown in a semi-arid area.
Fig. 1: Mean DBH, height, wood volume and aboveground biomass of hybrid poplar clone OP-367 (a Populus deltoides x P. nigra cross) grown under four irrigation levels from 2007 to 2012. Irrigation Levels 1-4 = 70, 80, 120 and 130% of replacement crop evapotranspiration (ETc), respectively. NMSU Agricultural Science Center at Farmington, New Mexico, USA. 2012.
5 Discussion Finding plantation species that are suitable for semi-arid climates and which provide marketable products within a timely rotation window, is challenging. Based on our study’s findings, hybrid poplar is adaptable to a semi-arid setting, given suitable clonal germplasm and drip irrigation scheduling. In particular, P. deltoides x P. nigra (DxN) crosses appear to be well adapted to this region of the semiarid Southwest. Clone OP-367 appears to be the highest producer, and surpassed a 10-year commercial target of 25 cm DBH after only 8 years (in another ASC trial). Likewise, clone 544 appears to be particularly drought-tolerant, as more recent ASC research on the current trial has indicated. Chlorosis issues from Fe deficiencies have been evident in some specimens, although DxN crosses appear to be able to overcome this challenge with initial fertigations of micronutrients and subsequent vigorous root growth. There are many angles from which to speculate about how to increase adaptability and growth of hybrid poplars in a semi-arid setting. However, research on hybrid poplar selection for the Southwest is still in its infancy. Mexal et al. (2002), for example, documented the use of municipal wastewater as a slow-rate land application system for growth of poplars at sites in Las Cruces, NM, and Ojinaga, Chihuahua, Mexico. They observed that selection of species and germplasm already adapted to an arid environment was crucial to system design. Another study, by Pearson et al. (2010), reported on the growth of eight hybrid poplar clones grown under short-term intensive culture: Populus nigra x P. maximowiczii (NM-6), P. trichocarpa x P. deltoides (52-225, OP-367), and P. deltoides x P. nigra (Norway, Noreaster, Raverdaus, 14274, 14272). They observed that OP-367 produced the greatest biomass (72.2 Mg ha-1) over the six-year period. Pearson et al. (2010) also observed that, depending on objectives, germplasm should be selected that is highly productive, possesses suitable tree architecture for production/commercial objectives, is appropriate for maximizing carbon sequestration, and is resistant to insect infestations and chlorosis problems. In addition, Grady et al. (2013), based on their provenance trials with P. fremontii in Arizona, emphasized the importance of identifying genotypes most suited to a predicted warmer climate and of understanding the physiological factors involved in adaptation to warm environments. Other possible approaches to success with poplars include use of biochar as a planting substrate, use of bacterial soil inoculants to provide for N fixation, and experimentation with new crosses and drought-tolerant varieties.
Conclusions/outlook This study has shown that drip-irrigated hybrid poplar can grow and flourish in a semi-arid area. Carefully managed drip irrigation can be used to grow poplars in a dry climate in an efficient manner, and can produce significant benefits in terms of marketable products and environmental services. The P. canadensis hybrid (a P.deltoides x P. nigra cross) has shown remarkable adaptability and growth in this harsh Southwestern environment, as well as in other environments. An irrigation level targeted at replacing approximately 120% of replacement ETc, based on calculations derived from conditions in east-central Oregon, was found to be best in terms of promoting tree growth and water use efficiency, in part because it serves as a cushion for mitigating occasional irrigation shortfalls resulting from human and system error. Overall, hybrid poplar may be considered for plantation and agroforestry production systems in semi-arid areas, provided that suitable germplasm is selected and BMPs are observed for dealing with drip irrigation, differing soil types, manpower needs, and distance to and feasibility of entering future commercial markets.
6 Acknowledgments The authors are grateful to the many NMSU staff and interns who have helped maintain the research site over the years. Funding was provided by the United States Department of Agriculture (USDA) Hatch Program through the National Institute of Food and Agriculture (NIFA), the US Bureau of Indian Affairs (BIA), the State of New Mexico, and the José Fernández Memorial Chair in Crop Production.
References Anderson JU. 1970. Soils of the San Juan Branch Agricultural Experiment Station. Research Report 180. Las Cruces, NM, USA: New Mexico State University Agricultural Experiment Station. Brady NC, Weil RR. 1999. The nature and properties of soils. Upper Saddle River, NJ, USA: Prentice Hall. Browne JE. 1962. Standard cubic-foot volume tables for the commercial tree species in British Columbia. Victoria, Canada: British Columbia Forest Service, 105 pp. CoHort. 2008. User's Manual. Monterey, CA, USA: CoHort Software. Gochis DJ, Cuenca RH. 2000. Plant water use and crop curves for hybrid poplar. Journal of Irrigation and Drainage Engineering, 126(4): 206-214. Grady KC, Laughlin DC, Ferrier SM, Kolb TE, Hart SC, Allan GJ, Whitman TG. 2013. Conservative leaf economic traits correlate with fast growth of genotypes of a foundation riparian species near the thermal maximum extent of its geographic range. Functional Ecology, 27(2): 428-438. Havlin JL, Beaton JD, Tisdale SL, Nelson WL. 1999. Soil fertility and fertilizers: An introduction to nutrient management. Upper Saddle River, NJ, USA: Prentice Hall. Jenkins JC, Chojnacky DC, Heath LS, Birdsey RA. 2003. National-scale biomass estimators for United States tree species. Forest Science, 49(1): 12-34. Keetch CW. 1980. Soil survey of San Juan County, New Mexico: Eastern part. US Department of Agriculture, Soil Conservation Service; US Department of the Interior, Bureau of Indian Affairs and Bureau of Reclamation; and New Mexico State University Agricultural Experiment Station. Lombard K, Maier B, Thomas FJ, O’Neill M, Allen S, Heyduck R. 2013. Wine grape cultivar performance in the Four Corners Region of New Mexico in 2010–12. HortTechnology, 23(5): 699709. Mexal JG, Zachritz WH, Sammis TW. 2002. Trees are the solution to wastewater treatment for small communities. In: Dumroese RK, Riley LE, Landis TD, technical coordinators. National proceedings: forest and conservation nursery associations: 1999, 2000, and 2001. Proceedings RMRS-P-24. Ogden, UT, USA: US Forest Service, Rocky Mountain Research Station, p. 327-335. Pearson CH, Halvorson AD, Moench RD, Hammon RW. 2010. Production of hybrid poplar under short-term, intensive culture in Western Colorado. Industrial Crops and Products, 31: 492-498. Smeal D, O’Neill MK, Owen CK, West MM, Allen SC, Arnold RN. 2014. Forty-three years (19692011) of climatological data: NMSU’s Agricultural Science Center at Farmington, NM. Bulletin 806. Las Cruces, NM, USA: New Mexico State University Agricultural Experiment Station, 44 pp.
