Occurrence of Sclerotium rolfsii Inducing Sugar Beet Root Rot and its Sustainable Management by Acting on Soil Fertility in Western Morocco

In Morocco, and particularly in the Doukkala irrigated perimeter, sugar beet rot caused by Sclerotium rolfsii is a major limiting factor for the productivity of this crop. The objective of this study was to identify the relationship between the frequency of Sclerotium rolfsii infestation and the quantity of viable sclerotia in the soil on the one hand, and with the different physicochemical parameters of the soil in cropped sugar beet fields on the other hand. In total, 1794 soil samples were collected during a four years period in the whole irrigated perimeter. These samples were analyzed for their sclerotial content. In addition, laboratory analysis of physico-chemical parameters was performed for 94 sugar beet fields in 2019. The study showed that the relative frequency of infestation by Sclerotium rolfsii and the number of viable sclerotia oscillate inversely and present a relative frequency of 45.7, 57.3, 42.3 and 49.5% for 2016, 2017, 2018, and 2019, respectively, and a number of sclerotia of 2.01, 1.65, 2.11 and 1.25 in 250 g of soil for 2016, 2017, 2018 and 2019, respectively. The study showed that the number of viable sclerotia was positively correlated with clay and silt content, soil pH, Mg, K, Fe, Cu, and Mn and negatively correlated with sand, SOM, EC, CaCO3, Zn, B, Ca, NH4 and NO3 contents. The observed decrease in viable sclerotia between 2016 and 2019 can be attributed to the decrease of Fe and Cu in the soil. It is possible that SOM intervenes with its humified fraction in the neutralization of the redox potential of Feand Cu which are involved in the production of sclerotia under oxidative stress. The good control of fertilization, especially organic, allows limiting the production of sclerotia of Sclerotium rolfsii. Data analysis allowed obtaining a significant prediction model of the number of viable sclerotia in the soil according to the physicochemical soil parameters with (R2 = 0.95 at P<0.0001) for only infested fields and (R2 = 0.87 at P<0.0001) for all the fields

New Approach for Mining Site Reclamation Using Alternative Substrate Based on Phosphate Industry By-Product and Sludge Mixture

Mining soils are generally characterized by soils having a coarse texture and low fertility, which makes revegetation a very difficult and delicate operation, especially in arid and semi-arid zones. The main objective of this work is to evaluate different substrates that can both contribute to the successful reclamation of phosphate mining soils and the valorization of phosphate by-product and sewage sludge. The study was carried out in pots under a greenhouse on Italian ryegrass (Lolium multiflorum). The experimental design is a randomized complete block with ten treatments, four repetitions from five substrates: phosphogypsum (PG), phosphate sludge (PS), sewage sludge (SS), topsoil from mining (TS) and phosphate waste rocks (PWR); this corresponds to soil after rock phosphate extraction. Nitrogen fertilization was applied to treatments after soil depletion in treatments not receiving sludge. An aerial biomass measurement and nutrient analysis were carried out for the three cuts. The results showed that a proportion of 65% of PG enriched the substrate in phosphorus by improving the crop yield. The addition of 5% of SS contributed to a significant improvement of ryegrass aerial biomass. In the absence of SS application, the addition of nitrogen is required to maintain crop growth. For large-scale application, TS can be mixed with PS, SS and PG for mine site reclamation

Study of the Sodicity of Phosphate By-Products and Sludge Mixture for Large-Scale Application in Mine Site Reclamation

Morocco has a very long mining tradition, and is threatened by ground salinization. The objective of this study was to evaluate the salinity level in the mixture of phosphate mining by-products and sludge prior to its use to reclaim a mine site or for soil remediation. The experiment was conducted with Italian ryegrass in 4 months under greenhouse. The design was a randomized complete block with 10 treatments and 4 replications. The results revealed that treatments containing phosphogypsum helped to reduce the effect of sodicity on soil. Thus, phosphogypsum associated with sludges can be used as an amendment to reclaim mine soil affected by sodicity