Blueberry Yield and Soil Mineral Nitrogen Response to Nitrogen Fertilizer and Nitrification Inhibitors under Drip-Fertigation Systems
Aimé J. Messiga, Sylvia Nyamaizi, Shaobing Yu, Martine Dorais
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.