Inorganic Fertilization at High N Rate Increased Olive Yield of a Rainfed Orchard but Reduced Soil Organic Matter in Comparison to Three Organic Amendments

Abstract

Strategies for waste valorisation from domestic and agro-industrial activities must be pursued, and its use as a soil amendment is an interesting possibility. In this four-year study, the effect of applying municipal solid waste (MSW), farmyard manure (FYM), bottom wood ash supplemented with nitrogen (Ash + N), the inorganic fertilization common in the region (50 kg ha−1 N, P2O5 and K2O) (Control) and this inorganic fertilization supplemented with 70 kg N ha−1 (High N) was assessed in a rainfed olive grove planted in a shallow soil with low organic matter and managed with conventional tillage. The High N treatment significantly increased olive yield in comparison to the other treatments (165% more than MSW), and soil available N proved to be the main driver for tree productivity. MSW and FYM increased soil organic matter, as well as the levels of phosphorus and cation exchange capacity, leaving good indications for future production cycles, although during the four years of the study these treatments provided little N to the trees. The High N treatment significantly reduced soil organic matter (63% less than MSW). The result was attributed in part to the soil management system that did not allow the development of herbaceous vegetation, but also to an effect known as “added N interaction”, in which the excess of inorganic N in the soil might have contributed to accelerate the mineralization of native soil organic matter, an aspect that compromises the sustainability of this fertilization strategy. Although MSW and wood ash are sometimes associated with risks of environmental contamination with heavy metals, in this study the levels of heavy metals in soils and in plant tissues were not of concern.

Dolomitic limestone was more effective than calcitic limestone in increasing soil pH in an untilled olive orchard

“…The increase of Mn in the leaves by the application of N fertilizers has also been previously recorded by Lopes et al (2021) in a soil developed from similar lithological materials. The bioavailability of Mn is also very sensitive to the redox potential of the soil (Sparrow & Uren, 2014).…”

“…However, this increase in the availability of P in the soil had little effect on the increase of P content in the leaves, since only on the last sampling dates of the Lburied experiment did the effect appear consistent, and especially in the Lmag treatment, which had a more pronounced effect on soil pH. Other studies have shown that some trees, including olive, may hold P in the perennial structure (Ferreira, Rodrigues, et al, 2018;Lopes et al, 2021;. Perhaps this buffering effect of the perennial structure, regulating the nutrient concentration in the shoot, associated with the slow action of lime application in the soil, is the reason for this very delayed effect of liming on the P concentration in the olive leaves.…”

Olive Yield and Physicochemical Properties of Olives and Oil in Response to Nutrient Application under Rainfed Conditions

“…Previous studies have shown that fertilizer application can play an important role in olive yield, but not all studies have found consistent results [ 13 , 14 , 23 , 24 ]. For instance, Erel et al [ 25 ] reported that fruit set and olive yield was negatively affected by N deficiency but not by K. Under N deficiency, these authors observed a reduction in olive yield, probably due to a decrease in protein biosynthesis, which is important for the development of the inflorescences.…”

“…Leaf concentration of macro and micronutrients from leaf samples taken at the end of the experiment, in December 2019, as a function of fertilizer treatments [with NPKB (control) and without N (N0), P (P0), K (K0) and B (B0)], and respective sufficiency range (SR) for the resting period of olive, after LQARS [22]. Previous studies have shown that fertilizer application can play an important role in olive yield, but not all studies have found consistent results [13,14,23,24]. For instance, Erel et al [25] reported that fruit set and olive yield was negatively affected by N deficiency but not by K. Under N deficiency, these authors observed a reduction in olive yield, probably due to a decrease in protein biosynthesis, which is important for the development of the inflorescences.…”

“…Although an adequate application of fertilizes can positively affect photosynthesis and whole-tree physiology, growth and olive yield [ 9 , 11 , 12 , 13 , 14 ], its effect on oil quality is scarce and inconsistent, especially under rainfed conditions [ 15 , 16 ]. Still, some trends can be highlighted.…”