The effect of digestate and wood ash mixtures on the productivity and yield quality of winter oilseed rape

It is important to provide winter oilseed rape (Brassica napus L.) with the required nutrients for successful growth. Biogas plants and solid fuel boilers widely used for energy and heat production create wood ash and digestates as by-products. In agriculture, both wood ash and biomass digestate are used separately as liming and fertilizer materials, while mixtures of digestate and ash can provide a high-quality fertilizer that increase the productivity and yield quality of various agricultural crops including winter oilseed rape. Field trials were conducted in the autumn of 2020 at the Study and Research Farm “Peterlauki” (56°53' N, 23°71' E) of the Latvia University of Life Sciences and Technologies. Soil has the following characteristics: sod calcareous soil, granulometric composition – heavy dusty sand clay. Soil agrochemical parameters: pH KCL 6.7 (LVS ISO 10390: 2006); organic matter content – 26 g kgE−1 (by Tyurin method, LV ST ZM 80–91), phosphorus content – 60 mg kgE−1 P2O5, and potassium content – 144 mg kgE−1 K2O (according to Egner–Rhym method, LV ST ZM 82–97). Winter oilseed rape sowings were developed using different variants of fertilizer mix with cattle (from SIA “Ziedi JP”) manure digestate (GD) and wood ash (P) (from SIA “Green Jelgava”) in different ratios [digestate used : wood ash ratio – (B1 – GD; B2 – GD + P 1:1; B 3 – GD + P 2:1; B 4 – GD + P 3:1; B 5 – GD + P 3:1 + N16P40K60 kg haE−1; B 6 – GD + P 3: 1 + N 68.8 kg haE−1; B 7 – GD + P 4:1)]. The norms of innovative mixed fertilizer for cattle manure digestate and wood ash were the following: A1 – 5 t haE−1; A2 – 10 t haE−1; A3 – 20 t haE−1. Winter oilseed rape fields without fertilizers and bovine manure digestate (GD) fertilizer rates were used as control options. Variants in the two-factor trial were randomized in triplicate. Studies have shown that good winter rapeseed yields can be obtained without the use of mineral fertilizers using wood ash and digestate mixtures. The highest winter rapeseed yield in the observed time period was obtained from variants where fertilizer rates of 10 t haE−1 were used. Winter oilseed rape seeds had a higher oil content in the variants in which 5 t haE−1 fertilizer mixtures was utilized. The bulk density of winter rape seeds in the studied variants this year wawas only slightly higher than 67.0 kg hLE−1. The aim of the study was to determine the effect of different digestate and wood ash mixtures on the productivity and yield quality of winter oilseed rape.