Abstract
In blueberry plantings, nitrification can result in losses of mineral nitrogen (N) through leaching because blueberries prefer ammonium (NH4+) over nitrate (NO3−). The objective of this study was to assess the effects of two rates of N fertilizer, mixed or not with nitrification inhibitors (NI) and applied through two fertigation systems, on berry yield and the concentrations of NH4+-N and NO3−-N along the soil profile. Thus, nine combinations of treatments including two N fertilizer rates (60 and 120 kg N ha−1), two NI (with DCD + Nitra-pyrin or without) and two fertigation application methods (buried and suspended drip lines) and a control (0 kg N ha−1) were tested over three years (2016–2018) in a long-term blueberry planting. Berry yield was on average 47.32 Mg ha−1 in 2016 and 26.86 Mg ha−1 in 2018. In 2017, berry yield varied between 8.60 Mg ha−1 under the control and 11.66 Mg ha−1 with 120 kg N ha−1 applied through suspended drip lines. Low berry yield in 2017 was due to a heavy pruning to rejuvenate the plants. In 2016, the concentration of NH4+-N in the sawdust mulch layer varied between 13.1 and 27.1 mg kg−1 in the spring, 11.4 and 32.1 mg kg−1 in the summer, and 7.9 and 72.9 mg kg−1 in the fall; the concentration of high NH4+-N along the soil profile did not exceed 5 mg kg−1. High concentrations of NH4+-N in the sawdust mulch layer were associated with NI, but did not translate to high berry yields. The concentration of NO3−-N in the soil profile reached 42.6 mg kg−1 in the summer and 39.0 mg kg−1 in the fall and these high concentrations were associated with NI. In 2017 and 2018, there was no effect of NI on NH4+-N concentrations even in the layer of sawdust mulch which was not consistent with the results obtained in 2016. High concentrations of NO3−-N were measured beneath the sawdust mulch layer with treatments including N fertilizer alone or mixed with NI. It is possible that NH4+ retained in the layer of sawdust mulch and not taken up by plant roots was subsequently oxidized to NO3− at the end of the residence time of NI in the soil. Our results showed that high concentrations of NO3−-N along the soil profile occurred mainly during the summer which could be explained by irrigation water driving NO3− leaching.
Highlights
Nitrogen (N) fertilization is a key management practice in agricultural production systems
In 2016, the combinations of treatments consisting of 60 kg N ha−1 and 120 kg N ha−1 combined with Nitrification inhibitors (NI) and applied through suspended drip lines had the highest concentrations of NH4+-N in the sawdust mulch layer (Figure 2b,c)
Our results showed that high concentrations of NO3−-N were measured beneath the sawdust mulch layer with treatments including urea fertilizer alone or mixed with NI, indicating a conversion of NH4+ to NO3
Summary
Nitrogen (N) fertilization is a key management practice in agricultural production systems. Ammonium (NH4+) based fertilizers applied to soils are transformed through nitrification into NO3− via nitrite (NO2−) by nitrifying microorganisms [1,2] This process is key for most plants with a preference for NO3− absorption, but poses a risk for the environment because residual soil NO3− not absorbed by plant roots is likely to be lost through leaching into surface and ground waters [3]. Min et al [10] in a study aiming at understanding N-dynamic pathways in order to achieve practical, useful recommendations recently showed that application of urea and Nitrapyrin significantly decreased N leaching by 37, 27 and 28% and soil residual NO3−-N contents by 34, 44 and 44%, under lettuce, celery, and tomato, respectively. Li et al [9] found no effect of NI on seed and lint yield in cotton production under drip-fertigation in a dry climate
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