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Plant nutrition is one of the factors that can influence fruit yield and quality. Brazilian soils are generally highly weathered, acidic and have low natural fertility with generalized nutrient deficits, especially of phosphorus (P) and potassium (K). The use of alternative sources of nutrients such as rock powder and mining co-products, when applied together, can increase the efficiency of soluble sources of P and K, and could reduce the need for soluble fertilizer imports that are often expensive and have low residual effect in the soil. Thus, the aim of this study was to evaluate MBR matrix fertilizer rates on fruit quality and plum cultivation, cv. Irati. This study was conducted at the UTFPR Campus Pato Branco, from 2009 to 2014. The experimental design was a randomized block with four replications and three plants per plot. Treatments (Tn) were: recommended chemical fertilizer replacement (T5); 2/3 of the recommended fertilization plus: 0 (T1), 500 (T2), 1000 (T3) and 2000 (T4) kg ha−1 yr−1 of MBR matrix; and without replacement (T6). Characteristics of plant quality, productivity and development, as well as leaf and soil contents of P and K were evaluated. The annual application of 1,000 kg ha−1 of the shale-based fertilizer matrix can be used as a complement to 1/3 of the P and K fertilization, in ‘Irati’ plum cultivation, by increasing accumulated production by 21.4%, maintaining the quality of the fruits, and maintaining adequate soil levels of P and K. The results demonstrate that the use of mining co-products of the Irati Formation has the potential for being used in agriculture as a source of nutrients, contributing to an increase in the efficiency of soluble sources of P and K, reducing the dependence on imported nutrient inputs and increasing local sustainable development..

Farmers are increasing the use of fertilizers in chestnut, the only cash crop produced in the mountainous areas of northeastern Portugal. This calls for more studies to guide them towards a more ecological intensification. The effects of three controlled-release fertilizers, two that release nutrients over three months (BoskGrow 20:05:20_3m, Exactyon 18:05:13_3m) and one over six months (Exactyon 18:05:12_6m), and an organic amendment authorized for organic farming (Humix 12:03:05) were compared with an untreated control during a three-year field trial (2019–2021). BoskGrow 20:05:20_3m, Exactyon 18:05:13_3m and Humix 12:03:05 gave significantly higher nut yields (90.6 to 97.0 kg tree−1, average 2019 + 2021) than Exactyon 18:05:12_6m (66.3 kg tree−1) and the control (69.5 kg tree−1). Leaf concentrations of nitrogen and potassium tended to be higher in the BoskGrow 20:05:20_3m and Exactyon 18:05:13_3m treatments, and they were stated as the most important causes in the establishment of the two productive groups. Humix 12:03:05, although less concentrated in nutrients, led to a chestnut yield at the level of the most productive treatments, possibly due to the multiple positive effects of organic matter on soil and plants. Under the conditions of this experiment, where rainfall is low in the summer, fertilizers whose nutrient release takes a long time, such as Exactyon 18:05:12_6m, seem not to be a good fertilization option due to reduced nutrient uptake and increased levels of soil inorganic nitrogen at the end of the growing season. Humix 12:03:05 emerged as a possible solution for organic producers.