Effects of drip irrigation and fertilizer levels on photosynthesis in cashew

The treatments of five irrigation levels (0, 20, 40, 60 and 80 l/tree once in four days from December to March) in main plot and four levels of NPK fertilizers (no fertilizers, 250 g N, 62.5 g each of P₂O₅ and K₂O; 500 g N, 125 g each of P₂O₅ and K₂O; and 750 g N, 125 g each of P₂O₅ and K₂O) in sub-plot were imposed. Microclimate, photosynthesis and leaf water potential were determined in fully matured leaves (2 to 3 months old) seven and eight years after planting in December and March. Soil moisture at five depths (0–25, 26–50, 76–100, 101–125 cm) was also determined. Irrigation did not affect microclimate and photosynthesis in December mainly due to presence of moisture within available range at deeper depths in control plot also. Transpiration, photosynthesis and stomatal conductance were significantly higher in irrigated and fertilizer applied tree than in unirrigated tree receiving no fertilizers in March. The reduced levels in photosynthetic parameters in unirrigated trees were associated with higher air/leaf temperature and lower relative humidity during March. In March, moisture stress below the lower level of available moisture was observed in control plot receiving no irrigation. Leaf water potential did not vary significantly due to irrigation and fertilizer treatments both in December as well as March.