Abstract
The objective of this study was to assess the energy efficiency of nitrogen fertilization in durum wheat and sorghum grains in the period 2017-2019. Bulgarian durum wheat variety Predel was studied at a stationary fertilizer trial on soil type Pellic vertisols at the Institute of Field Crops in Chirpan, Bulgaria. Grain sorghum hybrid EC Alize was investigated on the experimental field of the Agricultural University of Plovdiv, Bulgaria, on soil type Mollic Fluvisols. The crops were grown under non-irrigated conditions. The studied nitrogen rates were 0, 60, 120, 180, and 240 kg N.ha-1. In durum wheat, nitrogen was applied two times: one third at sowing, and the rest - as top dressing in the tillering stage. In sorghum, the total nitrogen was applied as pre-sowing fertilization before sowing. The nitrogen fertilizer was applied as NH4NO3. The experimental design was a randomized, complete block design with four replications with a size of experimental plots of 20 m2 for both crops. The energy efficiency of nitrogen fertilization (h) was calculated as the ratio between the received energy from additional grain yield of wheat and sorghum, respectively, and the invested energy from fertilization. It was established that energy efficiency of nitrogen fertilization depended on the nitrogen rate and hydro-thermal conditions during the vegetation period of durum wheat and sorghum. The bioenergy coefficient of durum wheat widely varied from 0.79 (N240 in 2018) to 4.44 (N60 in 2017). The average for the period, the highest value of energy efficiency of nitrogen fertilization was obtained at the low rate N60 The higher nitrogen rate of 240 kg N.ha-1 was slightly effective. Under drought conditions during the vegetation period of sorghum, most effective was the application of rates N120 with the highest energy coefficient of 1.23. The application of 180 kg N.ha-1 to sorghum was the most energy efficient under the favorable hydro-thermal conditions in 2018 and 2019, and the average for the period 2017-2019. A low N60 rate in grain sorghum was inefficient from an energy point of view. Durum wheat showed higher energy efficiency of nitrogen fertilization compared to grain sorghum.
Highlights
The intensive agricultural technologies and increased yields are accompanied by an increase in the cost of non-renewable or exhaustible energy
The amount of additional yield of durum wheat and sorghum grain resulting from the applied nitrogen fertilization of 60, 120, 180 and 240 kg N.ha-1 depends on the weather conditions during the growing season of the two crops
Nitrogen fertilization on durum wheat at a rate of 180 kg N.ha-1 resulted in the highest additional grain yield in 2018 - 1700 kg.ha-1 and in 2019 - 2450 kg.ha1
Summary
The intensive agricultural technologies and increased yields are accompanied by an increase in the cost of non-renewable or exhaustible energy. In an energy crop context, sustainability in crop production could aim at enhanced energy output with maintained or reduced depletion of N resources (Pourazaria et al, 2015). The manufacture of mineral fertilizers, package, transport and usage occupy about 45% of the used energy in agriculture (Mudahar and Hignett, 1987). In this context, the used fertilizer is equivalent to the input energy in agricultural production. Nitrogen fertilization is a main cost of non-renewable energy sources in agriculture and in terms of insufficient energy resources it is important to find ways to increase its energy efficiency (Hosseinpanahi and Kafi, 2012). According to Piringer (2006) in the total energy input of US grown wheat, the share of only nitrogenous fertilizer was 47 %, whereas in a study of Australia, the share of all fertilizers (i.e. nitrogen, phosphorus, and potash) was 47 %
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