AMMONIUM/NITRATE RATIO EFFECTS ON DRY-MATTER PARTITIONING AND RADIATION USE EFFICIENCY OF CORN

Physiological responses of plants to ammonium (NH4) versus nitrate (NO3) nutrition can vary considerably. A greenhouse study was conducted to examine the effect of ammonium-nitrogen/nitrate-nitrogen (NH4-N/NO3-N) ratio on dry matter partitioning and radiation use efficiency in corn (Zea mays L.). The hybrid Funks G 4673A was supplied with nutrient solutions that contained 8:1, 1:1, or 1:8 ratios of NH4-N/NO3-N. At each of four harvests, plants were separated into leaf blades, stem + leaf sheaths, and roots. Radiation use efficiency was calculated from these dry matter harvests and measured photosynthetically active radiation. Generally, more dry matter was partitioned to the stem than to leaf tissue when supplied with the 1:8 NH4-N/NO3-N ratio than when supplied with the other N treatments. Corn supplied with 8:1 and 1:1 ratios of NH4-N/NO3-N resulted in radiation use efficiency values for total dry matter that were significantly higher by 39 and 25%, respectively, than that of corn supplied with the 1:8 ratio indicating that Funks G 4673A was more efficient in converting radiation into dry matter when supplied with high proportions of NH4 than when supplied primarily with NO3.