Leaf Photosynthetic Response to Foliar Fertilizer Applied to Corn Plants During Grain Fill 1

Foliar fertilization of field crops has received renewed interest as a method of increasing seed yield by supplying additional nutrients to the leaves to delay the normal depletion of nutrients in the leaves during reproductive stages. It has been hypothesized that application of foliar fertilization may delay natural leaf senescence. We tested this by estimating leaf photosynthesis in field‐grown corn ( Zea mays L.) plants using a 14 CO 2 uptake procedure. A small segment of the leaf material enclosed in a chamber is exposed to 14 CO 2 for a short time period. Leaf samples are then analyzed using standard radiotracer techniques. In 1976 and 1977 14 CO 2 uptake rates were measured on a number of days between silking and plant maturity in conjunction with a larger experiment relating the response of corn to foliar fertilizer application and soil moisture deficits. The experimental plants were field‐grown in a Nicollet loam soil (an Aquic Hapludoll, fineloamy, mixed, mesic). These measurements indicated that the rate of leaf photosynthesis was depressed by as much as 17% the day following foliar‐fertilizer application, but had nearly recovered by the 2nd day. A similar pattern occurred in leaf conductance. No difference in the seasonal trend of photosynthetic rate was detected between control and foliarfertilizer treatments. Photosynthetic patterns after foliar‐fertilizer application may warrant further investigation, as significant yield reductions were noted in these experiments. Because the technique used in our experiments monitors rate of photosynthesis on small, intact leaf segments, totalcanopy photosynthesis and transpiration measurements could reveal helpful information.