**4. Discussion**

This work has found that of the three fertilisers under study and for all the crops included, phosphate fertilisers tend to have a relatively stronger linear relationship with yields. Wheat records the most significant relationship with fertilisers and more specifically in the case of phosphates (p-value = 0.05). Phosphate fertilisers are obtained from phosphorus rocks that are essential in crop growth and food cultivation. Phosphorus fertilisers constitute a strong element in Moroccan agriculture. Phosphorus is essential found in just a handful of countries around the world, with Morocco being the number one producer of phosphate fertilisers followed by China [27, 28]. About 70% of the global distribution of phosphate rocks will be depleted within the next 100 years. Morocco, with >77% of global phosphorus rock reserves, will need to increase production by 700% to be able to meet its deficits by 2075 [27, 28]. Invariably, Morocco's reserves accounted for almost all the increases in the global reserves of phosphate rocks [28, 29]. Morocco will have to increase its production to be able to meet the local and international demand for phosphate fertilisers. This work has assessed the recent trends in the linear relationships between the yields of the concerned crops and fertilisers and water withdrawal. This approach is important because as in the case of Morocco, as an arid country in which agriculture is mainly rainfed, water and nutrient management are key drivers of crop yields. However, there is need for more analysis with several variables on the climatic and non-climatic spectra to be able to better understand these trends. Perhaps therefore, the key contribution here is that yield prediction based on a few variables as in the case of this work does not often yield good outputs as yields are complex and generally impacted by a complex combination of several factors. In the current scientific literature, it remains unclear how these components of nutrient and water management play out in determining crop yields. For example, there are no national scale studies that have integrated components of nutrient and water management in yield prediction. Existing studies have either focused on nutrients or water management mostly in the context of irrigation [30]. A better understanding of this relationship will play a crucial role in determining how well yield gaps can be closed through nutrient and water management. In other words, this work sets the pace for a better understanding of the combinations and the need for more research for improved insights into such relationships on nutrient and water or irrigation that can be used to close future yield gaps. By understanding the linear trends between yield and nutrients or water, it becomes possible to identify where the linear trends are weak and which combinations of irrigation and nutrients can be used to close such gaps. The only other study that comes close to this is the work published in 2012 in Nature by Muller et al. [30] as it examines the use of nutrient and water management strategies to determine yield gaps using essential non-linear regression models at a global scale. Our work builds on the same strategy but focuses essentially on Morocco for which the global study did not dwell in detail.

In Morocco, it is important to however understand that there exists a spatial variation in crop yield as are climatic conditions. Normally, from south to north, crop yield increases for most crops. This has been explained by the south–north spatial variations in climate. This is seen as a straddle from south to north shows increased precipitation and lower temperatures due to the presence of the Atlantic Ocean and the Mediterranean Sea. Furthermore, sociodemographic data have also shown that due to its European and temperate influence, the north has higher literacy and lower poverty rates. This mix of climatic and non-climatic variables plays an important role in determining crop yields. The results have shown that in most cases, the changes in

yield are explained by relatively small changes in fertilisation as depicted by the R2 . There is a need to identify how much, when and where nutrients and water are needed to improve crop yields. This is especially true as many of the farmers involved are essentially small-scale farmers who do not have access to nutrients and irrigation. Wheat, on the other hand, has a relatively more significant relationship with phosphate fertilisers when compared to the other crops because the crop has been more valorised over the years as it is not just a major staple crop, but it also plays an important economic role in the country. Therefore, this work helps us to understand which crops need more valorisation in the context of access and use of nutrients and water, insights that can help in the formulation of agricultural policy.

It is now evident from previous scholarship that the relatively stronger impact that phosphate fertilisers have on crop yield in Morocco in general and especially on wheat when compared to the other crops is highly tied to the country's dominance in the production of phosphate fertilisers, which is also tied to its huge phosphate rock reserves [27, 29]. Morocco is often described as the Saudi Arabia of phosphorus because it is blessed with huge phosphate rock reserves. It has been argued that comparing Morocco with Saudi Arabia in terms of Morocco's phosphate rock reserves is very simplistic as Morocco would be better compared with all OPEC (Organisation of the Petroleum Exporting countries) put together [31–33].

The current global reserves of phosphate rocks may last for an additional 300– 400 years. By this time, most countries would have exhausted their stocks. This global figure is hugely impacted by Morocco with a rock-phosphate ratio of close to 2000 years. Globally, the countries that currently have rock-phosphate ratios of less than 100 years are responsible for about 70% of the global production and continuous depletion will result in huge deficits [28]. China and the United States account for over 50% of the global production and these might be depleted within the next 60 years at the current rates of extraction. The delicate global phosphorus intricate situation that surrounds phosphate extraction is going to intensify as Morocco has an ever-greater share of global phosphate production [29, 34]. This has implications for food and phosphorus security unless new phosphate reserves can be accessed. This will further mean that the world will be more reliant on Morocco [28, 35].

In terms of the relationship between yield as a dependent variable and agricultural water withdrawal and fertilisers as independent variables, agricultural water withdrawals are observed to have a stronger relationship. Here, it can be concluded that agricultural water withdrawal as a proxy for irrigation in agriculture plays a very important role. As a management option for agriculture, water withdrawal plays a keen role in filling the gaps created by unreliable precipitation. Farmers in most arid and semi-arid countries and regions often depend on precipitation as the main source of water for their crops. However, due to climate change and other anthropogenically induced stressors such as unsustainable systems of farming, there is often not enough precipitation for crop growth for systems that are basically rainfed. The recent IPCC Sixth Assessment Report confirms this assertion when it notes that most of north Africa including Morocco will continue to witness declining precipitation and rising temperature under various Representative Concentration Pathways (RCP) scenarios [36, 37]. The government of Morocco, through the Green Morocco Plan (GMP) and the Generation Green Strategy (GGS), have subsidised irrigation to make it accessible for farmers at various scales. Irrigation is therefore a significant driver of agriculture in Morocco.

Within the pessimistic climate conundrum that necessitates irrigation and fertilisation, such water withdrawals are often based on surface water resources, groundwater resources and non-convectional water resources. The mean precipitation

#### *Recent Trends in the Yield-Nutrient-Water Nexus in Morocco DOI: http://dx.doi.org/10.5772/intechopen.112552*

records about 140 billion cubic meters per year [38, 39]. Evapotranspiration triggers a leakage of about 118 billion cubic meters per year. Natural water potential is estimated at about 22 billion cubic meters per year. In Morocco, the amount of economically exploitable water is 80% of the available water resources, revealing the constraints in water resources and the difficulties associated with their utilisation for agriculture [39]. For example, the hydrological regime of all basins is characterised by rife interannual variability marked by wet and dry sequences, interspaced with years of intense drought stress. The Ouergha basin, for example, is among the most productive basins in Morocco by virtue of its surface water flow variations of 2.5 billion cubic meters per year. Thus, the large regional differences in rainfall also trigger large surface water flow variations that vary from a few million cubic meters (MCM) with most arid basins in Morocco such as the Saharan basins, to about one billion cubic meters per year for the most water-rich basins. The Sebou basin in the north of Morocco, for example, holds 30% of surface and groundwater resources in Morocco. Although it represents only 6% of the total area of Morocco, 18% of the country's population lives within its frontiers [40, 41]. Internal water reallocations are applied to reduce the shortages in each river basin. About 0.3 million cubic meters per year is transferred from the Oum er-Rbia basin to dry areas in Tensift, essentially to sustain irrigation. Similarly, another 0.16 million metric cubic meters per year is transferred from the Sebou and Oum er-Rbia basins to support Bouregreg's domestic water needs in other parts of Morocco. Ground water, on its part, accounts for 20% of all water resources in Morocco. Aquifers cover about 80,000 km<sup>2</sup> , about 10% of the national territory. Total groundwater withdrawal is estimated at about 3170 million cubic meters per year. However, the huge water withdrawal stress here is exhibited as about 4.2 billion cubic meters per year are extracted (higher than the rate of recharge) [30, 42]. On a final note, non-conventional water withdrawal is governed by the National Water Plan, which aims to address issues of gaps between water demand and water supply through *inter alia* desalinisation of sea water. The establishments of plants to this effect have enabled the desalination of nearly 515 million cubic meters per year [30, 42, 43].

The generally weak relationship between yield and fertilisers on the one hand and water withdrawal on the other hand shows us that crop yield is not that simple. Crop yields are determined by a complex interplay of several variables including precipitation, temperature, soils, fertilisers, irrigation, crop pests and diseases and livestock. Isolating yield and a few independent variables may provide insights into how many of the changes in yield are explained by changes in fertilisers and irrigation, but it is good to caution that several variables often impact crop yields.

Phosphorus can also be released from compost, green manures and animal manures. These elements contain mineralised phosphorus and micronutrients that are easier for plants to use. These alternative ways of adding phosphorus to increase soil fertility are good but cannot independently match the phosphorus that is obtained from phosphorus rocks [30, 40–43]. Also, combining phosphorus rock with green manure crop buckwheat might have significant benefits but phosphate rock deposits will remain the main source of phosphate fertilisation. Incubated phosphorus rocks have been observed to increase phosphorus uptake in buckwheat crop but the buckwheat residues did not however enhance the yield of the next crop. It has however been observed that using green manure crops on different soils might produce more positive results, but the scale does not match natural phosphorus. Green manure crop like legumes might also perform better [30, 40–43].

In the case of inorganic fertilisers, the phosphorus is removed from the rock using acids, rendering the phosphorus more soluble and easier to absorb. The problem now is to employ the same technique in organic agriculture to see how organic farms can enhance the update of phosphorous—one of the three key micronutrients together with potash and nitrogen for plant growth. This is even more challenging as micronutrients have no substitutes and their absence might hamper plant growth [30, 40–43]. In fact, inorganic phosphorus can be obtained through farm-level recycling of organic materials such as composts, green manure and animal manures. Adding green manure residues to soils can increase mineralisation rates of phosphorus but, at the same time, low concentrations of residues often do limit crop demand. Using green manure crop species that have high phosphorus uptake can overcome this limitation. Buckwheat, for example, absorbs concentrations of phosphorus beyond its own needs such that excess of it is left in the soil for future use [30, 40–43]. This has evidently shown us that, the future of phosphorus fertilisation depends on natural phosphorus rocks and Morocco will continue to play an important role in the agricultural food-chain in Morocco.

## **5. Conclusions**

This study has shown that though fertiliser application and water withdrawals have a weak relationship with crop yields (indicating the need for valorisation), these inputs nevertheless potentially constitute key variables that can trigger a veritable agricultural revolution in Moroccan agriculture that needs to be investigated further. More specifically, this work has shown that phosphate fertilisers have strong impact on the yields of all the crops, especially wheat, relative to nitrogen and potash. With the reality of the depletion of phosphorus rocks across the world in the frame of the huge dependence of agricultural systems on phosphate fertilisers, several questions come to mind. For example, how can land use policy be streamlined to ensure that global agricultural systems continue to have the phosphates they need to thrive? What are the potential alternative sources of phosphorus away from the huge phosphorus deposits in Morocco? If the Moroccan phosphorus monopoly is maintained, what are the likely actions needed to ensure access to phosphate fertiliser for the rest of Africa without extreme high prices? These among others are some of the questions that come to mind when the likely future trends in the use and stock of phosphorus resources are considered.

However, this study focuses mainly on fertiliser use and irrigation; in reality, crop production is more complex than simplified here, as it is often impacted by a complex interplay of several climatic and non-climatic variables. Potential areas of further research however would estimate yield gaps using the relationship between actual and attainable yield towards closing yield gaps as well as the relationship closing the latter through nutrient and water management. The use of machine learning-based approaches to determine the drivers of crop yields with several climatic and nonclimatic drivers will go a long way in providing a balanced understanding of crop yields.
