Abstract
Biobased nitrogen (N) fertilizers derived from animal manure can substitute synthetic mineral N fertilizer and contribute to more sustainable agriculture. Practitioners need to obtain a reliable estimation of the biobased fertilizers’ N value. This study compared the estimates for pig slurry (PS) and liquid fraction of digestate (LFD) using laboratory incubation and plant-growing experiments. A no-N treatment was used as control and calcium ammonium nitrate (CAN) as synthetic mineral fertilizer. After 100 days of incubation, the addition of PS and LFD resulted in a net N mineralization rate of 10.6 ± 0.3% and 20.6 ± 0.4% of the total applied N, respectively. The addition of CAN showed no significant net mineralization or immobilization (net N release 96 ± 6%). In the pot experiment under vegetation, all fertilized treatments caused N immobilization with a negative net N mineralization rate of −51 ± 11%, −9 ± 4%, and −27 ± 10% of the total applied N in CAN, PS, and LFD treatments, respectively. Compared to the pot experiment, the laboratory incubation without vegetation may have overestimated the N value of biobased fertilizers. Vegetation resulted in a lower estimation of available N from fertilizers, probably due to intensified competition with soil microbes or increased N loss via denitrification.
Highlights
Synthetic mineral nitrogen (N) fertilizers have made an essential contribution in maintaining an adequate food supply for the growing world population
Addition of calcium ammonium nitrate (CAN) and pig slurry (PS) resulted in the highest biomass yields, being fresh weight (FW) 148 ± 7 g pot−1, DW 32 ± 1 g pot−1 in CAN treatment, and FW 141 ± 8 g pot−1, DW 32 ± 2 g pot−1 in PS treatment, while the addition of liquid fraction of digestate (LFD)
Aadirect directcomparison comparisonofofNNdynamics dynamicsbetween between conditions with and withvegetation was achieved through synchronous investigation using laboratory incubation out vegetation was achieved through synchronous investigation using laboratory incubaand and maize-growing pots.pots
Summary
Synthetic mineral nitrogen (N) fertilizers have made an essential contribution in maintaining an adequate food supply for the growing world population. While N supplied by synthetic mineral N fertilizers is 100% in mineral form, most biobased N fertilizers partly provide organic N, which can be directly taken up by plants [7] or become available for plants via microbial N mineralization and immobilization turnover (NMIT) [8]. The actual value of biobased N fertilizers depends on the content of mineral N, which is directly plantavailable, and the mineralizable organic N whose availability can be affected by the product characteristics (C/N ratio, organic C and N quality, etc.) [10,11], the target plants [12,13], and the soil microbial communities [14,15]
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