**Author details**

availability of P from RP. From the results it was found that with the application of *Aspergillus niger*, 59.7, 42.6, and 36.4% of the total P present in the RP was released in the case of the application of sugar beet wastes, olive cake, and olive mill wastewaters, respectively which was suggested to be due to the secretion of organic acids. Overall, the growth and yield of the plants was increased with the combined application of RP, *Aspergillus niger* and different agroindustrial wastes, i.e. sugar beet wastes, olive cake, olive mill wastewaters, and dry olive cake [27]. Series of field and pot experiments were conducted in our lab to check the combined effect of RP, compost and PSMs in increasing the growth and yield of wheat. From the results, it was found that the combined application of RP-enriched compost with PSMs could serve as an alternate source of P for increasing the growth and yield of many crops, thereby leading to sustainable agriculture and cleaner environment [29]. Recently, we have conducted a series of pot and field experiments and their results have clearly shown better improvement in growth, nodulation, and yield of lentil compared to conventional use of chemical phosphatic fertilizers

For sustainable agriculture, there must be a positive link between the nutrients applied to the soil and crop uptake. This link could be more firm and sustainable if we employ an integrated approach, i.e. the use of bio-augmented RP-enriched organic fertilizer. In this way, we would be employing a sustainable approach to meet the needs of crops for P in an environment friendly way. The use of this approach would not only be helpful in the restoration of degraded soils, but would also be helpful in minimizing organic wastes that could be composted to make organic fertilizer. The use of indigenous sources of RP would help minimize the energy use during its conversion into chemical phosphatic fertilizers. The product would help the farmers in reducing their expenditures to purchase chemical fertilizers, and would also reduce the import budget on national level. However, a few studies have reported its efficacy under pot and field conditions. More studies under controlled and field condition are needed to confirm these reports. Also there is a need to find the optimum ratio to mix organic fertilizer and RP, its time, and rate of application. Relative efficacy of different sources of organic fertilizers to make bio-organo-phos could also searched out. Their post-harvest effects on soil physico‐ chemical properties and on microbial community structure could also be found out in future.

A variety of organisms are involved in P cycling in soils, and microorganisms are probably the most important ones. However, most of the soil microbes have not been cultured success‐ fully [148]. In the future, new culture-independent methods like LMW RNA profiling and PCR based on nucleic acid composition are required to study the function and ecology of microbes involved in P cycling in soils [149]. The techniques mentioned have been found not only independent of culture media composition or growth phase of microorganisms but also are precise and reproducible. These techniques also made it possible to utilize different biotech‐ nological tools like amplification of targeted genes or to quantify their expression. Overall, these techniques have opened new horizons in order to solve out the puzzle related to

[31].

**9. Conclusions and perspectives**

124 Organic Fertilizers - From Basic Concepts to Applied Outcomes

Allah Ditta\* and Azeem Khalid

\*Address all correspondence to: ad\_abs@yahoo.com

Department of Environmental Sciences, PMAS, Arid Agriculture University, Rawalpindi, Pakistan
