LAUSR

Constrained nutrient supplies to plants grown in calcareous mineral soils are expected to diminish faster under a climate change scenario; therefore, we examined the potato vegetative and physiological responses to potassium (K) humate soil amendment applied in addition to the recommended doses of nitrogen-phosphorus-potassium (NPK) fertilizers. Hypothetically, K-humate regulates or improves NPK soil supplies and plant uptakes and hence, growth parameters of potato. Field experiments were conducted on potato (cv. Cardinal) grown at the Vegetable Research Farm, Bahauddin Zakariya University, Multan, Pakistan for two autumns (2010-2011). We used randomized complete block design with three repeats each of the NPK (0, 50, 75 and 100% of recommended dose: 120-80-80 kg ha) and K-humate (0, 8, 12 and 16 kg ha; 30% K) treatments. Individual soil NPK or K-humate application significantly improved (p  0.05) leaf chlorophyll content, final plant height, photosynthetic rate, stomatal conductance (Sc) and water-use-efficiency (WUE). We observed a significant interaction between NPK and K-humate for explaining additional significant improvements in these parameter values (except Sc; leaf chlorophyll 23%, plant height 41%, photosynthetic rate 34%, WUE 37%) as well as those of the number of leaves (55%) and leaf area (38%) per hill, and transpiration rate (27%). However, leaf chlorophyll content values in responses to 75 and 100% recommended doses of NPK did not differ significantly. Therefore, we conclude that K-humate can be used in calcareous soils in addition to the NPK fertilizer doses to mitigate the adverse effects of calcareousness (responsible for constraining the NPK uptake) by regulating the NPK soil supplies and plant uptakes, which improve potato vegetative and physiological growth parameters.