Sugarcane Leaf Spectra and Photosynthesis Responses to Millmud Application On a Sand Soil.

Sugarcane (Saccharum spp.) yields on sand soils in Florida are much lower than on organic soils and have no improvements during a recent 33-year period. A current study suggested that the sand soil with addition of millmud, a by-product from the sugarcane milling process, significantly improved sugarcane yields. The objective of this study was to determine leaf spectra and leaf photosynthesis of 7 sugarcane genotypes and one erianthus genotype on a Margate sand soil with and without millmud added at the rate of 1500 cubic meters per hectare prior to planting. The experiment was planted with soil treatments as main plots and genotypes as subplots in November 2007. Chlorophyll (SPAD), spectral reflectance, and photosynthetic rates were measured at the top visible dewlap leaves during growing seasons of the first- and second-ratoon crops in 2009 and 2010. Millmud application was mainly reduced leaf reflectance at 550 and 710 nm. Sugarcane genotypes showed considerable differences in leaf spectra compared to erianthus. Millmud significantly increased leaf SPAD readings (16%) and photosynthetic rate (63%) for the first-ratoon crop but not for the second-ratoon crop. Genotypic differences in leaf SPAD and photosynthesis were also detected. Of the tested genotypes, CPCL 01-0877 in both crops, CP 03-1912 in the first-ratoon crop, and TCP 02-4587 in the second-ratoon crop had highest, but CP 78-1628 and erianthus had lowest SPAD values. CP 01-2390 had highest and TCP 02-4587 had lowest leaf photosynthetic rates for both crops regardless of millmud treatments. Compared to other genotypes, CP 01-2390 and erianthus had much less responses to the added millmud in leaf SPAD readings and leaf photosynthetic rate. CP 01-2390 was the most adapted sand genotype. Therefore, selection of well adapted genotypes on sand soils based on leaf photosynthesis and yield performance will improve sugarcane yield and profitability on sand soils.