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Los efectos de las prcticas agrcolas sobre la calidad y la cantidad de nectar en coffea spp.
The effects of farming practices on nectar quality and quantity in Coffea spp.
In the developing world traditional low-input farming practices are being replaced with high-input practices as a way to increase yield. The environmental and economic impact of inputs has driven researchers to seek ways to minimize inputs while maximizing crop yields. In some crops, like Coffea spp., pollination plays an important role in yield. The purpose of this experiment is to compare nectar quality and quantity of Coffea flowers between low-
input and high-input farms, demonstrating a link between practices, pollination, and crop yield. I found that more traditional, low-input practices have higher sugar concentration than high-input practices (t = 2.82; p = 0.006). The mean sugar concentration for the high-input practice is 27.9% 3.0 and for the Low Input practice is 29.8% 3.4. Although, there was no statistical difference between nectar quantities (t = 1.35; p = 0.19), there was a trend toward higher quantities in low-input practices. The mean quantity for the high-input practice is 0.047 0.02 mm and for the low-input practice is 0.07 0.13 mm. Though preference studies in pollinators, like honeybees, (Apis mellifera) show bees cannot distinguish between nectars of less than 4%, perhaps patches with higher quality nectars receive
better pollinator service and impact farm yield. The more traditional, low-input farm has 2% higher yields. Though data suggest a link between management and nectar quality, further study is needed to more directly link reward, pollinator service and yield.
En los pases en desarrollo las practicas tradicionales de poco impacto estn siendo remplazados por tcnicas de mayor impacto como una forma de incrementar su produccin. Los impactos ambientales y econmicos de las tcnicas de cultivo han llevado a los investigadores a buscar formas de minimizar el impacto y aumentar la produccin. En algunos cultivos, como el caf la polinizacin juega un papel importante en la produccin. El objetivo de este experimento fue comparar la calidad y la cantidad del nctar en las plantas de caf, para demostrar un enlace entre las prcticas del cultivo, la polinizacin y la produccin.
Text in English.
Pollination by bees
Polinizacin por abejas
Rendimiento de cultivos
Tropical Ecology 2009
Low-input farming practices
High-input farming practices
Ecologa Tropical 2009
Prcticas de bajos insumos agrcolas
Prcticas de altos insumos agrcolas
Servicio de polinizadores
t Monteverde Institute : Tropical Ecology
1 The effects of farming practices on nectar quality and quantity in Coffea spp. Jennifer Carter Department of Ecology/Evolutionary Biology, and Environmental Studies, University of Colorado at Boulder ABSTRACT In the developing world traditional low in put farming practices are being replaced with high input practices as a way to increase yield. The environmental and economic impact of inputs has driven researchers to seek ways to minimize inputs while maximizing crop yields. In some crops, like Coffea spp. , pollination plays an important role in yield. The purpose of this experiment is to compare nectar quality and quantity of Coffea flowers between low input and high input farms, demonstrating a link between practices, pollination, and crop yield. I found that more traditional, low input practices have higher sugar concentration than high input practices t = 2.82; p = 0.006. The mean sugar concentration for the high input practice is 27.9% Ã°Â± 3.0 and for the Low Input practice is 29.8% Ã°Â± 3.4. Altho ugh, there was no statistical difference between nectar quantities t = 1.35; p = 0.19, there was a trend toward higher quantities in low input practices. The mean quantity for the high input practice is 0.047 Ã°Â± 0.02 mm and for the low input practice is 0 .07 Ã°Â± 0.13 mm. Though preference studies in pollinators, like honeybees, Apis mellifera show bees cannot distinguish between nectars of less than 4%, perhaps patches with higher quality nectars receive better pollinator service and impact farm yield. T he more traditional, low input farm has 2% higher yields. Though data suggest a link between management and nectar quality, further study is needed to more directly link reward, pollinator service and yield. RESUMEN En los paÃses en desarrollo las prÃ¡c ticas tradicionales de poco impacto estÃ¡n siendo remplazados por tÃ©cnicas de mayor impacto como una forma de incrementar su producciÃ³n. Los impactos ambientales y econÃ³micos de las tÃ©cnicas de cultivo ha llevado a los investigadores a buscar formas de mini mizar el impacto y aumentar la producciÃ³n. En algunos cultivos, como el cafÃ© la polinizaciÃ³n juega un rol importante en la producciÃ³n. El objetivo de este experimento fue comparar la calidad y cantidad del nÃ©ctar en las plantas de cafÃ©, para demostrar el n exo entre las prÃ¡cticas de cultivo, polinizaciÃ³n y la producciÃ³n. EncontrÃ© que las prÃ¡cticas tradicionales de bajo impacto llevan a plantas con mayor concentraciÃ³n de azÃºcar que las de alto impacto. TambiÃ©n habÃa una tendencia a que las prÃ¡cticas de bajo i mpacto tenÃan mayor cantidad de nÃ©ctar . A pesar de que en algunos estudios en abejas Apis melifera , demuestran que detectan diferencias menores a las encontradas, tal vez las plantas con mayor calidad de nÃ©ctar tienen mayor Ã©xito de polinizaciÃ³n y esto af ecta su producciÃ³n. AdemÃ¡s la plantaciÃ³n con tÃ©cnicas tradicionales de bajo impacto tienen cosechas 2% mayores . A pesar de que los resultados sugieren un nexo entre las prÃ¡cticas de cultivo, la calidad y la cosecha del nÃ©ctar se necesitan mÃ¡s estudios .
2 INTRODUCTION Economics and population induced demand drive farmers to increase agricultural crop output Tilman et al ., 2002. I see this as more economic than population. There is competition in the marketplace that should favor maximizing y ield no matter what. For example, the application of synthesized, petroleum based, fertilizers has allowed cereal production to double in the last 40 years Tilman et al ., 2002. In addition, the proper use of organic matter and irrigation management can increase crop yields Sparks, 2007; Howell et al. , 1990, as well as the correct time of planting crops and higher diversity in crop rotations Tilman et al ., 2002. Farming practices impact yields by impacting plant health. For example, addition of fe rtilizers generally increase yield by increasing overall plant size and growth rate Altieri and Nicholls 2002. However, heavily fertilized crops can sometimes result in greater herbivory, because the fecundity and/or survival of herbivores often increa ses with foliage nitrogen content Drinkwater et al. , 1995. Thus, the application of insecticides, which reduce herbivory, and fungicides, which reduce disease, are beneficial to plant health Drinkwater et al ., 1995. Also, herbicides reduce competiti on by eliminating weeds Dawson 1964. The variety of these practices, including organic and non organic versions, allow for various management options. Another possible reason differing practices impact yield may be their effect on nectar and pollinati on. Plant health could impact nectar quality and quantity, affecting pollination services, and yield production. Nearly one third of our food supply by volume depends on the pollination done by bees Kremen et al. , 2004. If inputs cause differences in nectar quality and quantity, pollinators might favor one farm over the other, thus affecting crop yield. For instance, between adjacent flower patches of Delphinium nelsonii bumblebees have been shown to spend more time utilizing the patch with higher rat es of net energy intake Zimmerman, 1983, adjusting their foraging efforts to the quality and quantity of available resources Gill et al. , 2007. Moreover, bees are able to associate rewards with, and discriminate between, flowers within 4 5% difference in sugar concentration Waddington and Holden, 1979. Further, pollinators fly to closer flowers when there is more nectar per flower Zimmerman, 1983, which keeps them in the patch longer. One main crop that relies on bee pollination is coffee, Coffe a spp . Honeybee pollination can boost Coffea crop yields by over 50% Roubik, 2002. For instance, over 36% of Coffea production is consistently controlled by bees because the fruit set depends on cross pollination Roubik, 2002; Klein et al. , 2003. Th is study looks at two different coffee farms, a farm that uses fertilizer inputs and a low input farm that uses nitrogen fixing crops and organic matter as its only soil treatment, to determine if these practices cause a difference in nectar quality and qu antity. METHODS Study Sites I compared on two Coffea arabica Rubiaceae farms in San Luis de Monteverde, Costa Rica during the dry season. One was a two he ctare farm owned by Olvilio Ram i rez, located across from the cemetery at 1150 m in elevation. His practices on this farm include applying synthesized fertilizers, including 103010, occasionally adding an herbicide called Roundup,
3 manually cutting weeds, and no irrigation. Therefore, I refer to this farm as a high input farm. Though inputs here ar e likely far lower than in large monocultures of coffee, the inputs are higher than the other farm used for comparison. The other is a 3,000 m 2 , low input farm owned by Alvaro Leit Ã³ n, and is located at the end of Finca La Bella at 1250 m elevation. His p ractices include, planting nitrogen fixing crops, such as Guava Inga spp., Mimosaceae trees, manually cutting weeds, and using organic plant matter from the farm as nutrient input. In addition, the farmer informed me that he occasionally irrigates depen ding on rain patterns, which is rare due to the fairly consistent rainfall in the tropics. Also, a week before my experiment there was a storm, so the plants had not been irrigated before or during this research. Both farms have similar layouts in that t here is an edge of forest surrounding their crops on the northeastern side. I strategically selected plants in full sun on both plantations to control for energy input that might affect nectar production. Both farmers informed me of their estimated annua l yields. Nectar Measurements I covered multiple buds with mesh fabric to restrict insects, and returned every day at the same time to collect data from flowers that had opened for the first time each morning. When the flowers opened I carefully extrac ted the nectar from the bottom of the corolla by removing the sepals and placed the nectar on an Extech RF15 refractometer to measure nectar concentration. This reports nectar concentration in % sucrose by volume. For my quantity test, I used filter pape r to quantify relative nectar amount. To measure, I placed the nectar as it was being removed from the flower on its corresponding unit and I measured, in millimeters, the width of each nectar mark. But this is relative nectar quantity. To get this to a ctual quantity, you would have to spot known amounts of nectar on filter paper and make a standard curve. I used a statistical t test to analyze my data. RESULTS At each farm, I bagged 114 flowers, 58 for quality and 56 for quantity. However, some flow ers did not have enough nectar to detect sugar quality and were left out of the data set. In the end, for each farm my data consists of 41 flowers for quality and 56 for quantity. The mean sugar concentration for the High Input farm was 27.9% Ã°Â± 3.0 and f or the Low Input practice was 29.8% Ã°Â± 3.4. The mean quantity for the high input practice was 0.047 Ã°Â± 0.02 mm and for the low input practice was 0.07 Ã°Â± 0.13 mm. The low input practice had a significantly higher sugar concentration than high input practice Figure 1; t = 2.82; p = 0.006. There was no significant statistical difference found in the nectar quantity Figure 2; t = 1.35; p = 0.19. However, there seems to have been a trend toward higher nectar quantity in the low input practice Figure 2. Furthermore, the low input farm had a slightly higher estimated annual crop yield, 0.15 Kg/m 2 , compared to the high input farm with an estimated annual crop yield of 0.115 Kg/m 2 .
4 FIGURE 1. The mean sugar concentration Ã°Â± SD of nectar in Coffea flower s located on low input and high input farms in San Luis, Costa Rica during the dry season N = 85. FIGURE 2. The mean quantity Ã°Â± SD of nectar in Coffea flowers located on low input and high input farms in San Luis, Costa Rica during the dry season N = 114. 20 22 24 26 28 30 32 34 High-Input Low-Input Practice Type Sugar Concentration % 0 0.03 0.06 0.09 0.12 0.15 0.18 High-Input Low-Input Practice Type Nectar Quantity mm
5 DISCUSSION One reason that sugar concentration is higher in low input practice farms might be due to the positive affects organic matter has on soil chemical and physical properties Bationo and Mokwunye, 2005. For example, plant residue has s ignificantly higher concentrations of nutrients than synthesized fertilizers Bationo and Mokwunye, 2005. In addition, the decomposition of this organic matter leads to a continual release of nutrients available for plants Liebman and Davis, 1999. Thi s nutrient rich soil could give rise to healthier plants that are able to invest more energy into nectar production. In contrast, the application of synthesized fertilizers in a high input practice farm gives an initial boost of nutrients to the soil, but this is short lived as they are washed away with the rainfall, especially in the tropics Sisworo et al ., 2004. In turn, this leads to lower quality soil, which could affect plant health resulting in low investment in nectar production. While irrigati on may have an influence on my results, it would be minimal due to the storm prior to my study, and therefore the lack of irrigation while I collected my data. Higher sugar concentrations in nectar, up to some maximum, beyond which it is too thick, are mo re preferable to Coffea s most abundant pollinator, honeybees. This optimal foraging sugar concentration is 30% Tezze and Farina, 1999. They also prefer larger nectar quantities Zimmerman, 1983. Therefore, 30% sugar concentration and higher quantity nectar would result in more pollinator visits and potentially higher yields. However, bees discriminate against nectar at a minimum of 4% difference in sugar concentrations and thus 2% is not sufficient enough to cause a disadvantage for high input practi ces Wadding and Holden, 1979. Therefore, future research with longer studies, more specific practices in question, and variables held constant, needs to be done. Most importantly, in demonstrating that differing practices affect nectar quality and, pos sibly quantity, this study opens the door to a new component in assessing the impact of inputs. Especially, for the developing world where increased demands have resulted in the traditional, low input, management for important cash crops, like Coffea , Kl ein et al., 2003 to continually be replaced by less traditional, high input practices with the intention of producing higher yields. As land is being altered and environmental impacts are increasing the need for assessing the costs and benefits of using d iffering practices and their yield capacity is becoming more and more crucial. This is because, only when efficient practices are found will agricultural environmental impacts decrease and outputs become sustained. However, because pollination plays such an important role for crop yield understanding the affects these practices have on pollination will also be vital in assessing the costs and benefits in management practices. ACKNOWLEDGEMENTS Thanks Alan Masters for your help in advising me, answering a ll of my questions, and giving me incredible insight, Olvilio Ram i rez and Alvaro Leit Ã³ n for your kindness and access to your farms, Yi men Araya for your help on my statistics and translation with the farmers, and Leah Hirsch for your time and input into m y paper review.
6 LITURATURE CITED Bationo, A. and A.U. Mokwunye. 2005. Role of manures and crop residue in alleviating soil fertility constraints to crop production: with special references to the Sahelian and Sudanian zones of West Africa. Nutrient Cyc ling in Agroecosystems. SpringerLink. 29:1. 117 125. Dawson, J.H. 1964. Competition between irrigated field beans and annual weeds. Weeds. 12:3. 206 208. Jstor. Drinkwater, L.E., D.K. Letourneau, F. Workneh, A.H.C. van Bruggen, and C. Shennan. 1995. Fund amental differences between conventional and organic tomato agroecosystems in California. Ecological Applications. 54:1098 1112. Jstor. Gill, Mariana, Rodrigo J. De Marco, and Randolf Menzel. 2007. Learning reward expectations in honeybees. Learning and Memory. 14:491 496. Howell, TA, RH Cuenca, KH Solomon. 1990. Crop yield response [abstract]. In: Management of farm irrigation systems. American society of agricultural engineers. 93 122. CSA Illumina. Klein, A.M., I. Steffan Dewenter, and T. Tscharntke . Pollination of Coffea canephora in relation to local and regional agroforestry management. 2003. Journal of Applied Ecology. 40:5. 837 845. Jstor. Kremen, Claire, Neal M. Williams, Robert L. Bugg, John P. Fay, and Robin W. Thorp. 2004. The area requirements of an eco system service: crop pollination by native bee communities in California. Ecology Letters. 7:1109 1119. Liebman, M and A.S. Davis. 1999. Integration of soil, crop, and weed management in low external input farming systems. Iowa State University. 27 47. < http://220.127.116.11/scholar?hl=en&lr=&q=cache:cWaXVxKMV8oJ:agroecology.pbwiki.com/f/w eeds Liebman.pdf+decomposition+in+crop+residue+release+on+nutrients +>. Accessed 2009 May 13. Roubik, David W. 2002. Tropical agriculture: the value of bees to the coffee harvest. Nature. 417:708. Sisworo, Widjang H., M.M. Mitrosuhardjo, Havid Rasjid, an d R.J.K. Myers. 2004. The relative roles of N fixation, fertilizer, crop residues and soild in supplying N in multiple cropping systems in a humid, tropical upland cropping system[abstract]. Plant and Soil. 121:1. 73 82. SpringerLink. Sparks, Donald L. 2007. Advances in agronomy.< http://books.google.com/books?hl=en&lr=&id=N8G 1_ nVLSkC&oi=fnd&pg=PA197&dq=farm+practices+and+crop+yield&ots=oQEQQng7ax&sig=4zoo6AR Aa3XkGxqkrOFREsY1RkY#PPA236,M1 >. Accessed 2009 May 10. Tezze, Andrea A., Walter M. Farina. 1999. Trophallaxis in the honeybee, Apis mellifera : the interaction between visc osity and sucrose concentration of the transferred solu tion [abstract]. Animal Behavio r. 57:6. 1319 1326. Science Direct. Tilman, David, Kenneth G. Cassman, Pamela A. Matson, Rosamond Naylor, and Stephen Polasky. 2002. Agricultural sustainability and int ensive production practices. Nature. 418:671 677. Waddington, Keith D., Larry R. Holden. 1979. Optimal foraging: on flower selection by bees. The American Naturalist. 114:2. 179 196. Jstor. Zimmerman, Michael. 1983. Plant reproduction and optimal foragin g: experimental nectar manipulations in Delphinium nelsonii . Oikos. 41:1. 57 63. Jstor.