Effect of Pistachio Residue Biochar Prepared at Two Different Temperatures and Different Nitrogen and Phosphorus Levels on Some Macronutrients Concentration and Spinach Growth

Application of chemical fertilizer is one of the methods to supply nutrient elements for plants and it is an effective method to meet plants nutrients demands; but organic fertilizers such as biochar application can be used as a proper solution to decrease gases resulted from agricultural activities, increase soil's organic matters and to manage soil fertility. Biochar can increase soil fertility of some soils, increase agricultural productivity, and provide protection against some foliar and soil-borne diseases. Biochar is a high-carbon charcoal used as a soil amendment and it is made of plant biomass and produced during pyrolysis process in the absence of oxygen. The ability of biochar to store C and improve soil fertility will depend on its physical and chemical properties, which can be varied in the pyrolysis process (pyrolysis temperature) or through the choice of raw materials.
In order to study the effect of pistachio residue biochar produced in two different temperatures and chemical fertilizer on macronutrients concentration and growth of spinach (viroflay) (Spinacia oleracea), a greenhouse experiment was conducted in a factorial (2×3×3) arranged in a completely randomized design with three replications. Treatments consisted of three biochar levels (0, 3, and 6% by weight) prepared at two temperatures (200 and 400 °C), and three fertilizers level [0 (blank), (Nitrogen=80 and Phosphorous=15 mg kg-1 soil) and (Nitrogen =150 and Phosphorous =30 mg kg-1 soil)]. Bulk soil sample was collected from the surface horizon (0–30 cm) in Bajgah Agricultural Station of Shiraz University, Iran. Pots contained 2 kg dry soil. Treatments were added to all pots uniformly and were mixed. Then soil samples incubated in 25 ̊C for 30 days; and soil moisture was kept at about field capacity (FC). Following incubation time, based on soil analysis nutrients were added to all pots uniformly. Ten seeds were sown in each pot, and soil moisture was kept at about field capacity. Spinach seedlings were thinned to five uniform plants per pot 15 days after emergence. The pots were then maintained under FC. Plants were harvested after 8 weeks after emergence. Aerial parts of spinach plants were separated and oven dried and were weighed and ground. Total nitrogen (N), phosphorous (P) and potassium (K) in plants were measured. Statistical analysis was performed using SAS and Excel statistical software packages.
Results showed that biochar prepared at 200 and 400 ̊C had no significant effect on spinach dry weight (DW). Chemical fertilizer significantly increased average of spinach DW. Chemical fertilizers improved N and P concentration in plant, therefore increase growth of spinach than control. Biochar prepared at 200 and 400 ̊C significantly increased shoots N, P and K concentration of spinach compared to that of control; but biochar prepared at 400 ̊C had significant effect on shoots N and P concentration. Biochar might be direct nutrition resources for plant and supply many nutritional elements such as N, P and K for plant and increase concentration of these elements in plant. Application of chemical fertilizer significantly increased N and P and significantly decreased K concentration in spinach shoot. Several studies showed that application of biochar improved efficiency of nitrogen fertilizer in several soils and finally more nitrogen absorbed by plant. Biochar prepared at two temperatures had no significant effect on DW and shoot N concentration of spinach. However, addition of biochar prepared at 400 ̊C significantly decreased shoot P concentration and significantly increased shoot K concentration in spinach, as compared to biochar prepared at 200 ̊C.
Results indicated that application of biochar prepared at 200 and 400 ̊C improve composition of spinach but had no effect on its DW, probably because of short term of plant growth, kind of biochar, and biochor levels. Applications of biochar, increased shoot N and P concentration; it might be due to improving physical, chemical and biological properties of soil with addition of biochar. Also, biochar supplied nutritional elements and improve efficiency of chemical fertilizer; therefore it is appropriate that biochar applied with chemical fertilizers. Our results showed that 6% biochar level was the best suggested levels that in three chemical fertilizer levels increased shoot N and P concentration of spinach. With increasing temperature for preparing biochar, pH of biochar increased; so, it might be concluded that biochar prepared at low temperature was appropriate than biochar prepared at high temperature for application to calcareous soils.