Excessive Delay in Nutrient Release by Controlled-Release Fertilizers Can Reduce Chestnut Yield

Abstract

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.

Large Chestnut Trees Did Not Respond to Annual Fertiliser Applications, Requiring a Long-Term Approach to Establishing Effective Fertilisation Plans

“…If applying earlier, there is a risk of loss of mobile nutrients, such as N, by leaching and denitrification, whereas if applying later, there is a risk of loss of effectiveness due to reduced soil moisture [21]. In addition, slow and controlled release fertilizers tend to be less effective, as they delay nutrient availability for the summer, when the opportunity for root uptake is low [64].…”

Omitting the Application of Nitrogen or Potassium Reduced the Growth of Young Chestnut (<em>Castanea sativa</em>) Trees, While a Lack of Boron Decreased Fruit Yield

“…When N is deficient, plants clearly exhibit stunted growth [5,17]. In this region, where soils are typically shallow and low in organic matter and nutrients, significant differences in crop productivity often arise when comparing treatments that provide varying N rates [13,14,33].…”

“…In some municipalities of Portugal, chestnut is currently the only catch crop, playing a decisive role in reducing the depopulation of rural areas. While some studies have already been carried out in mature orchards to try to understand how to fertilize these gigantic trees [32][33][34], few have been devoted to studying the response of young plants to fertilization. This early stage of the tree's life is also important as fertilizers can increase the rate of canopy growth and the speed at which the trees begin to bear fruit.…”