Photosynthetic Characteristics and Productivity in Citrus. 1. Effect of Nutrition

Six years old cutting grown Pant Lemon-1 cultivar of Citrus Union Burrn. gave maximum growth and yield with the application of 100 g nitrogsn (N) along-with 50 g potassium (K) or 25 g phosphorus (P) per tree per year of age respectively when compared with other nutrient combinations. Highest photosynthetics rates (P_N) and ribulose-l,5-bisphosphate carboxylase (RuBPC) activity were obtained with the application of N alongwith K or P while minimum values were obtained with the application of K alongwith P, Photorespiration rates (R_P) were the highest with combined application of N, P and K and the lowest with the application of N along with P. Boron (Na₂B₄O₇.10 H₂0, 0.20 per cent; B), iron (FeS0₄, 0.40 per cent; Fe) and molybdenum [(NH₄)₆ MO₇O₂₄.4 H₂O, 0.10 per cent; Mo] increased P_N, R_P and RuBPC activity while manganese (MnS0₄, 0.40 per cent; Mn) and zinc (ZnS0₄, 0.50 per cent; Zn) had slight reducing effect. The highest P_N and RuBPC activity were obtained with B while R_P was the highest with Mo. The lowest Pn was recorded with Zn whereas minimum Rp and RuBPC activity were observed with Mn. Thus photosynthetic efficiency of C. Union (a C3 species) may be improved by judicious application of fertilizers.