عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Introduction Phosphorus deficiency is one of the major problems of calcareous soils in Iran and based on current statistics more than 70 % of all soils in Iran are under critical P levels of 15 mg kg-1 (51). Previous research results show that application of organic matter increases P availability (46) and changes the P distribution between various forms in calcareous soils.The aim of this study was to evaluate the effects of different levels of spent mushroom compost and sugar cane bagasse biochar as agricultural by products or crop residues on availability and phosphorus fractions in a calcareous soil from Karaj (Alborz provience, Iran).
Materials and Methods The soil for the experiment was obtained from 0-30 cm depth of Agriculture Faculty farm of Tehran University at Karaj. Some physical and chemical properties were determined using standard methods (table 1). The spent mushroom compost (SMC) was from Malard mushroom factory and Sugarcane bagasse was from a farm in Khozestan. The Biochar (B) was prepared from the raw material heated to 500 degree celcius inside furnace for 3 hours. Some basic properties of SMC and biochar were also determined (table 2). The experiment was conducted in a completely Randomized design with 5 treatments, and 3 time periods with three replications of each treatment. Treatments included 2 biochar levels B1, B2 (15 and 30 Mg ha-1 respectively), 2 spent mushroom compost levels SMC1, SMC2 (20 and 40 Mg ha-1 respectively) and the control treatment (C). For each treatment, 300 grams of air dried soil was used in small pots and after application of materials and mixing they were moist to field capacity and kept inside an incubator at 28-29 ˚C for a period of 120 days. At 14, 60 and 120 days soils were sampled for analysis (by eliminating the pots). Soil properties such as pH, available P, water soluble P and various inorganic P fractions (23) were determined in soil samples. Statistical analysis of the data was done using SAS software and mean comparison using LSD method was also performed.
Results and Discussion Results showed that the available P in the control increased significantly (p<0.01) from 8.8 mg kg-1 of soil to 17.8, 28.8, and 12.8 mg kg-1 of soil in the SMC1, SMC2, and B2 respectively, which had an increasing trend with time in B2, but in the SMC2 it was highest on 60 days. This can be related to higher microbial activity after application of organic materials and release of P after organic matter decomposition (22). The water soluble P also increased from 2.1 mg kg-1 in the control to 2.8 and 2.7 mg kg-1 in the SMC2 and B2 respectively, which showed an increasing trend over time for SMC2 (p<0.01). In the SMC treatments, part of the P content is in inorganic water soluble form and also in the biochar treatments some ash containing P soluble salts may be the source of increase in water soluble P content. The Ca2-P form in the control was increased from 5.1 mg kg-1 of soil to 11.1 and 16.2 mg kg-1 of soil in the SMC1 and SMC2 respectively, which had an increasing trend with time(p<0.01). During 120 days of incubation, the Ca8-P, and Al-P forms were also increased from 158 and 27 mg kg-1 of soil in the control to 186 and 35 mg kg-1 of soil in the SMC2 treatment (p<0.01). The distribution pattern of P fractions after application of SMC and Biochar was different and it changed with the level of the applied material.
Conclusions: Based on the results of this experiment application of organic materials of different nature such as spent mushroom compost and sugarcane bagasse biochar to calcareous soils can affect the availability and various forms of phosphorus to the extent that it should be considered as a measure to improve P availability conditions.