Nitrogen and phosphorus fertilization for jumbo (Sorghum bicolor × Sorghum sudanese) forage production and evaluation by using near infrared reflectance spectroscopy.

An experiment was conducted to investigate the effects of nitrogen (N) and phosphorus (P) fertilization on jumbo forage (Sorghum bicolor x Sorghum sudanese) production and to develop calibration equations by using near infrared reflectance spectroscopy (NIRS) for nutritional evaluation. Five levels of N fertilizer (0, 40, 80, 120 and 160 kg N ha -1 ) and three levels of P fertilizer (0, 10 and 20 kg P ha -1 ) were applied by 5x3 factorial arrangements in randomized complete block design. Sun-dried ground forage samples from 2 harvests (n = 90) were scanned by Fourier Transform-NIRS systems monochromator (700-2400 nm). Calibrations were developed by Partial Least Square (PLS) as regression method. Green biomass and dry matter yield of jumbo forages were found to be highest at 160 kg N ha -1 and 10 kg P ha -1 both in the first and second cutting. The root mean square error of estimation for the prediction of crude protein, acid detergent fiber, neutral detergent fiber and in-vitro organic matter digestibility by using NIRS of jumbo forage samples (n = 90) were 0.23, 1.57, 0.37 and 0.83% with correlation coefficients (r 2 ) were 94.0, 78.0, 95.0 and 84.0 respectively. Root mean square standard error of cross validation for the prediction of crude protein, acid detergent fiber, neutral detergent fiber and in-vitro organic matter digestibility in jumbo forage samples were 0.33, 1.63, 0.89 and 1.24% with correlation coefficients (r 2 ) were 83.2, 74.3, 67.0 and 60.2 respectively. Green biomass and dry matter yield of jumbo forage can be improved with the application of 160 kg N and 10 kg P ha -1 . NIRS may be an effective tool for quick