The recent export-driven increases in pecan price have renewed interest in the crop and led to the planting of additional pecan acreage throughout the U.S. pecan belt (USDA, 2012; Wells, 2014). A survey of pecan producers throughout Georgia documented the planting of 391,488 pecan trees and 15,328 additional pecan acres since 2010. The majority of these new pecan plantings are equipped with microsprinkler or drip irrigation systems equipped for fertigation (Wells, 2014).
Cultural practices that promote tree growth and vigor during the establishment phase are desirable for increasing tree fruiting surface. Irrigation and N fertilizer must be managed appropriately to achieve optimum tree growth and nut production, while ensuring minimal environmental impact. Historically, N fertilizer recommendations for young pecan trees in Georgia orchards have been minimal regarding the use of dry, granular fertilizer. Fertigation was discouraged because of the perceived potential for root damage from excessive concentration of N in the root zone (Wells, 2007). The prolonged period from tree planting to first commercial harvest of pecan provides incentive for many growers to intensively manage young trees to induce commercial production as soon as possible. This management includes high N application rates with or without fertigation. However, there remains very little data regarding the effect of N fertilization or fertigation on young pecan trees grown under southeastern U.S. orchard conditions.
Worley (1991) suggested that application of fertilizer to the backfill soil at transplanting did not affect caliper, height, or vigor of pecan trees. Photosynthesis and growth increased with N supply but was dependent upon leaf N:sulfur (S) ratio in a greenhouse study of pecan seedlings (Hu and Sparks, 1992). Conner (2007) found pecan nursery seedling height and caliper were unaffected by N fertigation except for the N rate of 40 g per tree, which suppressed seedling growth and that N needs of the seedlings were met by a preplant application of 50 lb/acre N applied as 10N–4.4P–8.3K.
Fertilizer N applied in excess of that needed to support optimum productivity accumulates in the soil and becomes increasingly vulnerable to a variety of loss mechanisms including leaching and denitrification. Excessive application of fertilizer N in orchards occurs when growers have a limited awareness of tree N use, soil N availability, tree N status, and the relationship between tree N status and tree capacity for N uptake (Weinbaum et al., 1992). Pecan trees in the first 2–3 years of establishment have a limited root system compared with more mature trees, thus their capacity for uptake of N and other nutrients is limited. In addition, most pecan nurseries maintain high fertility to shorten rotation time and increase nursery production (Conner, 2007). As a result, trees often maintain adequate levels of N through the first year following transplant to the orchard. The lack of proper soil moisture management and the nonresponsiveness of trees to excessive N fertilization are integrally related to N pollution of the environment (Weinbaum et al., 1992). The perception that annual applications of significant amounts of fertilizer N represent cheap insurance against the economic risks associated with insufficient N availability is common among growers.
Additional research is needed in the southeastern United States to evaluate the effects of fertigation on microsprinkler-irrigated young pecan trees compared with other forms of fertilization. The objectives of this study were to compare the effects of fertigation with more commonly recommended forms of fertilization on growth and N status of first- through third-leaf young pecan trees under microsprinkler irrigation.
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