Site-specific management of pH-induced iron chlorosis of maize

A study was conducted over nine site/years in Nebraska, USA between 2004 and 2005 to evaluate the potential to predict chlorosis-prone areas within fields which are relatively stable in space and time. The study also investigated the potential benefits of site-specific cultivar management according to chlorosis pressure. Sites were mapped for soil apparent electrical conductivity (ECa) at two depths (0-30 cm and 0-90 cm), and soil pH at a depth of 10 cm. Sites were also sampled by hand on a regular grid to a depth of 20 cm and analyzed for a range of soil properties. Sites were evaluated in-season with natural color and near-infrared imagery, and at the end of the season by yield mapping. In all or a portion of each field, replicated paired strips of two maize cultivars were planted, one considered susceptible to iron chlorosis (P34N42), another with similar characteristics but tolerant to iron chlorosis (P34B99). Detailed evaluation of the ability to predict iron chlorosisprone areas was conducted over 3 site/years. Management zones were delineated using combinations of yield data, ECa and vegetation indices derived from aerial imagery. Across all locations, grid sampled pH ranged from 6.1 to 9.1; on-the-go pH ranged from 4.9 to 9.2; shallow ECa ranged from 0.1 to 39 mS/m; deep ECa ranged from 0.2 to 152 mS/m. For one field, planted to maize one year and soybean the next, two chlorosis management zones were consistently delineated both years, with similar spatial relationships. For another field, soil water holding capacity was a larger yield limiting factor than iron chlorosis and management zones for iron chlorosis could not be delineated. For 8 site/years where paired strips of chlorosis-prone or tolerant cultivars were planted, no distinct advantage of site-specific maize cultivar management was found based on yield response of the two cultivars evaluated. Generally P34B99 yields were superior to P34N42 regardless of the level of chlorosis pressure. This study found spatial information on factors conducive to iron chlorosis can be useful in delineating chlorosis-prone areas within fields. However, other yield limiting factors may confound delineation of zones strictly for chlorosis management. Successful spatial cultivar selection for iron chlorosis management will require the use of cultivars with response characteristics which differ more than those used in this study.