Effect of Nitrogen, Phosphorus, and Potassium Fertilization on Nutrional Status of Fiber Hemp

This study was conducted to determine the optimum time for plant analysis, which can provide useful indications of nutrient deficiencies in plants, and to establish limit values for nutrient supplies to fiber hemp (Cannabis sativa L.). The effect of nutrient supplies on the nutritional status of fiber hemp was estimated by leaf analysis in a long-term field fertilization experiment at four nitrogen-phosphorus-potassium (NPK) levels on Chernozem meadow soil in Szarvas, Hungary, in 1999 (good water supplies) and 2003 (dry). The optimum time for the diagnostic analysis of fiber hemp was found to be late May or early June, when plants in the five- to -seven-leaf stage are 70-100cm in height, with a biomass of 2-5tha-1 dry matter, depending on water and nutrient supplies, variety, and production condition. Nutrient supplies to hemp can be considered satisfactory if plant analysis reveals 5-6% N, 0.5-0.6% P, and 2.7-3.0% K in the youngest fully developed leaves in late May. A stem yield (10% moisture content) of 12-17tha-1 was achieved when rainfall supplies were adequate (1999), whereas in the dry year (2003), the lower nutrient concentrations in the uppermost leaves, indicating nutrient deficiency, resulted in a maximum stem yield of only 6-8tha-1. The low, satisfactory, and high values for the concentrations of N, P, K, calcium, magnesium, iron, manganese, zinc, and copper reported in the article could be used to elaborate a fertilizer recommendation system for hemp.