Breadfruit has experienced an exponential increase of plantings in Hawai‘i (Langston and Lincoln, 2018) and an increase in distribution and cultivation globally (Lincoln et al., 2018). The Food and Agriculture Organization of the United Nations (2009) has recognized breadfruit as one of 35 priority crops for its tremendous potential to improve global food security, human nutrition, and climate-smart agriculture in the tropics (Lucas and Ragone, 2012; McGregor et al., 2016). As one of the few staple foods that grow on long-lived perennial trees, breadfruit has potential to dramatically shift cultivation practices in tropical regions away from annual crops. Breadfruit is highly productive, with consistent yields of at least 5 t·ha−1 edible dry weight [see Lincoln et al. (2018) for compilation of reported yields] and was an important element of Hawaiian food systems in the past (Lincoln and Ladefoged, 2014; Winter et al., 2018). Despite the growing interest and awareness of the production potential of breadfruit, it remains underused and suffers from significant lack of research investment (Lincoln et al., 2018; Ragone, 2007). Thus, substantial gains in breadfruit yield are probable with relatively little agronomic research and breeding effort (Sraffa, 2005; Willcox, 1954).
Foliar nutrient analysis is a well-established method (Munson and Nelson, 1990) to assist in the diagnosis of nutrient-related problems (deficiencies, toxicities, imbalances, etc.) of both annual and perennial crops. Assessment of foliar nutrient concentrations can be applied to inform fertilizer management, rule out nutrition as a source of a production variability, and assess the impact of management techniques on the nutrient status of crops. Foliar nutrient analyses are employed through tissue-sampling methods, which are contingent on sampling location, plant part selected, and the stage of growth. Specific sampling protocols may be dependent on the crop type and purpose (Munson and Nelson, 1990). Furthermore, optimal nutrient levels must to be established for each individual crop. Although important work has been done for many fruit crops (Jones, 2001), including species related to breadfruit (Poovarodom et al., 2000; Sun et al., 2015; Tawinteung et al., 2001), no studies investigating foliar sampling protocols for breadfruit were identified (Lincoln et al., 2018).
Using data from commercial and research orchards in Hawai‘i, we explored foliar sampling methods of breadfruit to inform a sampling protocol. Sampling entire breadfruit leaves is impractical due to their size (we have measured leaves up to 1.4 m in length). Thus, implementing a method that uses a portion of a leaf is necessary. Our primary objective was to assess leaf location and leaf part for suitability in foliar nutrient diagnosis and to validate potential sampling protocols using measurements of breadfruit productivity.
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