Soil and Leaf Nutrient Status of Selected Valencia Orange Orchards in the Gharb Plain of Morocco

Monitoring the nutrient status of citrus orchards is fundamental to ensure optimum fruit yield and quality. In the present study, soil and leaf samples of 20 Valencia Late orange orchards were collected in the Gharb plain of Morocco, the second-largest citrus area in the country. The objective was to assess the status of essential macronutrients (N, P, K, Ca, and Mg) and micronutrients (Fe, Zn, Cu, and Mn) in Valencia orange orchards and investigate the relationships between soil properties and nutrient contents in soils and leaves. Soils of the studied orchards had a medium to heavy texture, with low to moderate levels of organic matter content (6–31 g kg−1). They were also non-saline and mostly alkaline and calcareous. These soils exhibited a wide range of macro- and micronutrients. Suboptimum levels of total N, available Fe, and Cu were observed in most soils. Most of soils had also sufficient levels of available P, Mn, and Zn. All soils were sufficiently supplied with available Ca, Mg, and K. Similarly to soil analysis, leaf analysis indicated the prevalence of adequate to very high levels of P, Ca, Mn, and K. Leaf N and Fe status were below optimum levels in most orchards, which is in line with the observed low levels in soils. Nevertheless, unlike soils, leaves did not show any deficiency of Cu; instead, most orchards had adequate to excessive levels of this micronutrient. Additionally, leaf Mg and Zn status were deficient in most orchards, conversely to that of soils. This discrepancy between soil and leaf analysis was also noted in the lack of correlation we observed between soil nutrients and their respective levels in leaves. Correlation analysis revealed also an antagonistic interaction between K–Mg and Ca–Mg, which explained the widespread suboptimum levels of Mg in leaves despite its sufficient status in soils. Such antagonism was also observed between Fe–Mn. In the case of Cu, we suspect the use of Cu-containing plant protection products to contribute to the high levels in leaves despite its low levels in soils. Overall, our results showed that nutrient imbalances leading to antagonistic interaction heavily impacted nutrient status in our study area. We expect unbalanced fertilization to contribute to this issue. Therefore, fertilization practices should be managed judiciously to maintain an adequate nutrient balance in the soil and trees of citrus orchards and ensure their sustainable production.