Sugarcane Growth and Physiological Responses to Nitrogen Supply.

Yields of sugarcane (Saccharum spp.) grown on sand soils in Florida are lower than those on organic (muck) soils. Nitrogen supply may limit sugarcane yields on these sand soils. A 2-year pot study was conducted to determine genotype variation in response to N supply and effects of N fertilizer rate on leaf photosynthesis, plant growth, and dry matter accumulation on a sand soil. Treatments included four N rates (0, 75, 150, and 225 kg N ha^-1) and three sugarcane genotypes (CP80-1743, CP01-2390, and TCP87-3388). CP80-1743 and CP01-2390 were adapted for muck and sand soils in Florida, respectively and TCP87-3388 was a cultivar adapted in Texas. The experiment was a RCB design with five replications. Single-bud stalk sections of sugarcane were planted in pots filled with Margate sand soil and fertilized with P, K, and micro nutrients prior to planting based on soil analyses. Nitrogen fertilizer was equally split and applied at about 55 and 125 days after planting (DAP) for each treatment. During the experiment, the number of nodes and stalk length and tillers were recorded and leaf relative chlorophyll (SPAD) and photosynthesis components were measured biweekly. All plants were harvested at 183 DAP to measure green leaf area (GLA) and shoot biomass components. There were significant differences among genotypes in leaf SPAD, photosynthesis, GLA, and shoot biomass accumulation and partitioning. CP80-1743 had the least GLA, shoot biomass, and N use efficiency. Nitrogen rate affected leaf SPAD, GLA and biomass accumulation, but had less effect on leaf photosynthetic rate. Genotype × N interaction was only significant on green leaf biomass. GLA and biomass increased with increasing N rates. Therefore, selecting N stress tolerant genotypes with optimum N application can improve sugarcane yields on sand soils in Florida.