**1. Introduction**

Food production is crucial for our existence and every other life on earth. The rate at which phosphorus (P), a critical ingredient in growing food, is declining is alarming. It was estimated that existing rock phosphate reserves could be exhausted in the next 50–100 years [1–3]. Phosphorus is the second most likely nutrient deficient in the soils after nitrogen [3]. It is one of the most important nutrients for crop production. P availability is usually low in soils around the globe. Moreover, the low efficacy of P fertilizers in acidic and calcareous soils restricts P availability [4]. Recently, it has become increasingly difficult for small-scale farmers in developing countries to purchase chemical P fertilizers.

Rock phosphate is a sedimentary rock that contains high amounts of phosphorus. The rock is mined and in it contains clay and limestone [5]. Rock phosphate had a long history and had been used as organic fertilizer for gardens. It's known for keeping plants healthy and encouraging new growth [5]. Rock phosphate can be used as crude phosphatic fertilizer by direct application to field soil. It was established that double application of RP and phosphate-solubilizing fungi/bacteria improve P content in soil [6]. Moreover, the farmers in sub-Saharan Africa (SSA) are facing high prices of phosphate fertilizers because of the low solubility of the African RPs. Therefore, an affordable P fertilizer supply from local low-grade phosphate rocks would strengthen crop production in SSA and improve farmers' income.

Fungi play fundamental roles in regulating key ecosystem processes such as decomposition of organic matter and plant–soil relationship [7]. Arbuscular mycorrhizal fungi (AMF) on the other hand are widespread obligate plant symbionts that can colonize the roots of most land plants. They also assist in obtaining nutrients and protection against environmental stresses [8]. It was similarly reported that AMF symbiosis improves plant stress resistance and soil stability, making it a promising addition to sustainable agricultural practices [9]. It's crucial to develop a method to enhance P solubility in African degraded soils. There have been significant positive reports on application of partially acidulated RPs on crop cultivation including pearl millet, sorghum, cowpea and maize. It's well known that calcination of RP with Na carbonate increases its solubility, but this method is a classical option, which has been employed for ages in solubilizing low-graded RPs. It's well known that calcination with Na carbonate increases its solubility but proven difficult due to high content of impurities such as silicates [10].

There is need to develop knowledge on natural biological agents that may sustainably improve crop performance and lessen our reliance on technology [11]. AMF symbiosis may be optimized to improve the sustainability of agricultural systems by increasing the ability of crops to absorb soil P, resist pathogens, and tolerate drought stress [12]. AMF are among the microbial groups that could solubilize mineral phosphates and improve plant phosphorus nutrition. AMF inoculation was also reported to induce spectacular stimulations of the plant growth and phosphorus foliar content [13].
