The application effect of leonardite, vermicompost and black soils on the yield, yield components and concentration of some nutrients in green pepper (Capsicum Anuumm L.)

Abstract
Background and objectives: In order to increase the quantity and quality of plant production in sustainable agriculture system, the co-application of organic and inorganic (chemical) fertilizers are in great importance. The co-application of organic and chemical fertilizers could potentially increase both plant growth and crop yield by improving the soil quality properties and enhancing the uptake of plant nutrients. In this approach, a proportion of needed plant nutrients is supplied by the chemical fertilizers and the rest is provided by organic fertilizers. Meanwhile, in this study the co-application of the organic i.e leonardite, vermicompost and black soils and their extracted humic acid and the inorganic fertilizers were studied. The main objective of this study was to investigate the effect of co-application of some organic amendments and chemical fertilizer on yield, yield components and concentration of some nutrients in green pepper.
Materials and methods: To investigate the effect of co-application of some organic amendments on the yield and yield components of green pepper, a split-plot design over randomized completely design in three replications at pot-experiment level was conducted in 2019 growing season. In this experiment, the main factors include three types of organic amendments (leonardite, vermicompost and black soil) and sub-factors were 14 levels including (control, chemical fertilizer treatment (NPK) according to soil test, leonardite in three levels (2.6, 5.2 and 7.8 ton ha-1), extracted humic acid from leonardite in three levels (2.6, 5.2 and 7.8 kg ha-1), leonardite at the level of 2.6 (ton ha-1) with 75 % of needed chemical fertilizer (NPK), leonardite at the level 5.2 (ton ha-1) with 50 % of needed chemical fertilizer, leonardite at the level of 7.8 (ton ha-1) with 25 % of needed chemical fertilizer, extracted humic acid from leonardite at the level of 2.6 (kg ha-1) with 75 % of needed chemical fertilizer, humic acid extracted of leonardite at the level of 5.2 (kg ha-1) with 50 % of needed chemical fertilizer and the humic acid extracted of leonardite at the level of 7.8 (kg ha-1) with 25 % of needed chemical fertilizer were considered. Furthermore, all sub-surfaces for vermicompost and black soil treatments were similar to those for leonardite treatment.
Results and Discussions: The results indicated that co-application of organic amendments and chemical fertilizers and its interaction effect had significant effects on yield, yield components and concentration of nitrogen, phosphorous and potassium of green pepper fruit. Application of extracted humic acid from leonardite (2.6 kg ha-1) with 75 % of NPK was able to increase yield of pepper, plant height, leaf area and total leaf chlorophyll 6, 1.7, 2.3 and 2.7 time compared to the control. Also, the highest amount of nitrogen, phosphorus and potassium of green pepper fruit increased by 7, 2.8 and 2.9 times in the above treatments compared to the control, respectively.
Conclusion: The co-application of organic fertilizers and/or extracted humic acid with chemical fertilizer increase the concentration of high elements such as nitrogen, phosphorus and potassium in green pepper fruit as well as vegetative traits such as plant dry weight, plant height, chlorophyll content and leaf area in green pepper. In fact, leonardite and extracted humic acid due to the increased root uptake and the chelating ability of the element, will make these elements more available to the plant. In general, the combined application of humic acid and chemical fertilizers (NPK) due to the richness of nutrients required for plant growth of green pepper compared to the control treatment.