Changes in Soil C/N Ratio and Response of Growth of Hemp (Cannabis sativa L.) to Different Levels of Animal Manure and Chemical Fertilizers

IntroductionHemp is used in the food, drug, and natural fibers. Assessment of various systems of plant nutrition is one of the ways to improve field management and production of medicinal plants. Nitrogen is considered a necessary element in plant nutrition. Nitrogen uptake as ammonium compounds form, serves as starting material for amino acid biosynthesis and additional N-containing compound such as pyrimidine, purine bases, chlorophyll, proteins, nucleic acid, vitamins and other organic compounds, therefore, the higher plants require larger amount of nitrogen. Phosphorus is the second most important nutrient in plants. Studies show that application of animal manure provides different nutrients for plants. Application of animal manure in soil at the optimal level for plant growth provides a opportunities for soil fertility, conservation, sustainability, and protection against degradation but they need time to release their nutrient. Various studies showed that the combined usage the animal manure and chemical fertilizers (like N and P) has positive effects on soil, growth and yield of plant with the aim of protecting the environment. Organic and inorganic fertilizers are effective on soil C/N ratio. Soil C/N ratio is important factor for plant and soil. It is important to study the different stages of plant growth responses to organic and chemical fertilizers for plants production. Therefore, the present study was undertaken to evaluate the effect of organic amendments enriched with chemical fertilizers of nitrogen and phosphorus and studying changes of soil C/N ratio in vegetative and reproductive stages of hemp.
Materials and MethodsTo study the effect of different levels of animal manure and chemical fertilizers, a split factorial experiment, based on complete randomized blocks design with three replications was conducted at the Research Farm of Faculty of agriculture, University of Birjand, during the growing season 2013-2014. Experimental factors were animal manure (0, 10, 20 and 30 ton ha-1 well-rotted farmyard manure) as the main plot, and factorial application of three levels of N (0, 50 and 100 kg N ha-1 as Urea) with two levels of P (0 and 80 kg P2O5 ha-1 as triple superphosphate) as sub-plot. Hemps were planted on rows 60 cm apart, with 30 cm distance between plants within a row, at the depth of 3-4 cm. In during experiment didn’t use any poison and pesticide. Measurements were performed in both vegetative (11th leaf pair) and reproductive (50% of seeds hard) stages. Measured traits included leaf, shoot weight, shoot height and diameter per square meter in sub-plot for female plants of hemp in vegetative and reproductive stages. Seed weight measured in reproductive stage too. Nitrogen of soil was determined by Kjeldahl method and soil carbon was measured by Walleky & Black method. Finally, all variables were analyzed by SAS software ver 9.1. The means were compared using LSD test at the 0.05 probability level.
Results and DiscussionThe results showed that the measured traits were not affected by animal manure in the vegetative stage, but nitrogen fertilizer had significant effect on growth traits in this growth stage. Using manure and nitrogen fertilizers increased height and shoot diameter, leaf and shoot dry weight in reproductive stage. Biological and seed yield increased with increasing of nitrogen levels in different treatments of 0, 10 and 20 ton ha-1 animal manure. Combined usage of 30 ton ha-1 animal manure and 100 kg N ha-1 decreased biological and seed yields. Combined usage of 30 ton ha-1 animal manure and 50 kg N ha-1 and 20 ton ha-1 animal manure and 100 kg N ha-1 increased biological and seed yields. Harvest index decreased with increasing rate of animal manure and nitrogen fertilizers. So harvest index decreased 18.20 and 13.07 % in treatments of 30 ton ha-1 animal manure and 100 kg N ha-1 respectively, due to increasing the growth of hemp. Leaf allocation increased with increasing animal manure and nitrogen fertilizer levels. Phosphorus increased seed yield (13%), shoot dry weight (42.6%) and leaf dry weight (15.21%) in the reproductive stage. Soil C/N ratio decreased with increasing growth of hemp. In reproductive stage, using animal manure decreased C/N ratio due to release of nitrogen to the soil.
ConclusionsCombined usage of manure and chemical fertilizer were more effective than manure alone. Animal manure and nitrogen fertilizer were effective on soil C/N ratio. Results indicated that combined use of animal manure and chemical fertilizers must be done carefully and use of appropriate amounts of animal manure and chemical fertilizer can be effective in reducing the use of chemical fertilizers.