## 1 Introduction  
Agricultural production requires regular use of inorganic fertilizers. However, inorganic fertilizers are increasingly scarce and difficult to obtain from natural resources; additionally, their excessive application increases soil and water contamination and may contribute to create unsustainable food systems when the nutrient flows are badly used [1]. Therefore, the use of waste products appears to be an optimal option for enhancing nutrient soil restoration [2]. Even though agricultural macronutrient flows (N, P, and K) are controlled mainly by inorganic fertilizers, other nutrient resources, such as atmospheric deposition, crop waste, and livestock manure, represent major inputs, which are still largely unknown [3, 4]. Additionally, cover crops constitute a good strategy of supplying essential nutrients that contribute to more ecologically sustainable management, particularly in the context of organic farming practices [5]. Studies concerning Na, Ca, and Mg dynamics in soils after the spreading of crop wastes report correlations among these nutrients and with soil quality [6]. Nevertheless, data on the inputs of micronutrients (Fe, Mn, Cu, and Zn) are widely unavailable. Micronutrients are as essential as macronutrients for crop development and their deficiency causes multiple imbalances in the plant's physiology. Micronutrient fertilizers are applied mainly in soluble forms, such as chelates, fertilizing mixtures, or sprays. However, these soluble compounds are frequently lost by leaching and are not assimilated by the crops [7]. As another essential element for agrosystem soil improvement, organic matter contributes to soil structure development and consequently to soil's water retention capacity [8], among other important physical and biological properties [9; 10]. In addition, soil C sequestration in the form of organic matter efficiently helps mitigate climate change [11; 12]. Pruning waste can provide nutrients to crops. This contribution depends on the nutrient amount as well as the composition and decomposition rate of the waste [13]. The decomposition of plant remains is vital in ecosystems and, besides releasing nutrients, this material also increases the content of soil organic matter [14], thus enhancing soil quality. Tree crops generate large amounts of wastes that are traditionally incinerated, with the consequent loss of some nutrients and C [15]. The application of crop debris on the soil surface helps to reduce soil erosion, increase soil C sequestration, and return part of the nutrients to the environment, thereby promoting more sustainable agriculture [12]. This also applies to garden wastes that, in certain areas, such as the subtropical coast of Andalusia (S Spain), can be used for nutrient supplementation. Among other factors, the waste quality depends on the C:N and lignin:N ratios [6; 16; 17], the P and K contents [18; 19], and the lignin proportion [20]. As shown in previous studies [21], nutrient release can alter soil microbial activity. This has been reported for activities of enzymes such as \(\beta\)-glucosidase and dehydrogenase [22], as well as urease and phosphatase, over time periods longer than six years [23]. In previous studies performed on the subtropical coast of Andalusia (S Spain) [24], we have demonstrated that pruning waste from avocado, mango, cherimoya, and gardens are mineralized depending on their C:N ratios and hemicellulose, cellulose, and lignin contents, in agreement with other authors [18]. In the present study, our hypothesis is that nutrient release from pruning waste is controlled by several factors, including initial concentrations of C and N, soil quality, microclimatic characteristics, and soil microbial activity that can be detected through changes in soil enzymatic activities. The aim of this work is to study the time course of nutrient release to the soil after the addition of bagged pruning waste of subtropical crops (avocado, cherimoya, and mango) and urban garden waste over three two-year periods.