|Authors: ||A. Schwarz, J. Pfenning, W.-A. Bischoff, H.-P. Liebig|
|Keywords: ||Nitrochalk, ENTEC® 26, Self-Integrating Accumulators, groundwater quality|
The Nitrogen (N) input for intensive vegetable production is higher than for other agricultural crops.
The anion nitrate has a high potential to contaminate groundwater due to its mobility in the soil.
Two strategies to minimize N leaching are tested: (1) Slow release fertilizers (e.g., ENTEC® 26), and (2) late ploughing in winter (e.g., 01.02.). The influence of fertilizer strategy and ploughing date on nitrate leaching and yield parameters are analyzed in an ongoing perennial field experiment.
We chose two fertilizing strategies (Nitrochalk and ENTEC® 26) and three fixed ploughing dates (01.12., 01.01. and 01.02.). Two vegetable crops are cultured followed by winter rye as a catch crop each year.
N fertilization was calculated as 80% of the recommended amount for both fertilizer strategies.
The nitrate leaching was measured continuously in 60 cm depth in semi-annual intervals using Self-Integrating Accumulators (SIA). Three years of ley farming lead to a high soil organic N content.
The high mineralization potential caused high nitrate leaching.
The mean annual nitrate leaching is lower for Nitrochalk (223 kg N ha-1 a-1) than for ENTEC® 26 (266 kg N ha-1 a-1), but not significantly.
We assume that the nitrification inhibitor in ENTEC® 26 is inactivated by sorption to the clay fraction.
Mean nitrate leaching during all years decreased with later ploughing date: 263 kg N ha-1 a-1 (01.12.), 250 kg N ha-1 a-1 (01.01.), and 135 kg N ha-1 a-1 (01.02.). In three of four winters, the nitrate leaching maximum was observed in the treatment with the highest temperature during one week after ploughing and not for the earliest ploughing.
Therefore, the temperature within one week after the ploughing event is suspected as co-factor.
The differences in nitrate leaching at different ploughing dates are caused by soil organic N stock changes due to mineralization.
Yield decreased for late ploughing (01.02.).
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