Nitrogen Dynamics in Conventional Versus Twin Row Silage Corn.

More than 80 % of the 1.1 M ha agricultural land base in the humid region of Atlantic Canada is used for silage or forage production, either in support of the livestock industry or in rotation with other crops. In corn (Zea mays L.), a major environmental and agro-economic concern relates to the inefficient utilization of nitrogen (N), a problem which has been compounded in recent years by the sharp rise in the price of N fertilizers. Improving the retention of soil nitrogen capital in manure-fed corn silage systems is therefore important, both from an environmental as well as an economic perspective.

The objective of this study was to compare the N usage efficiencies of manure-fed, conventional row corn (CRC) versus twin row corn (TRC) management systems on a tile drained soil in Atlantic Canada at the same N application rate. In the first year of the study, three major N loss components were determined, namely removal of N in the silage harvest, nitrate leaching and denitrification losses, while a fourth, ammonia volatilization in the period subsequent to manure application, was estimated using a model. Silage yield and quality was used to measure of economic sustainability. Our hypothesis was that the twin row system with a higher plant population and greater rooting density per unit volume of soil would utilize N more effectively than its conventional row counterpart, but without reductions in yield and silage quality.

The two corn systems were grown in a randomized complete block experiment with three replications.  Liquid dairy manure (LDM) was applied uniformly to all plots at a target rate equivalent to 150 kg N ha^-1 and incorporated with tillage. A further 50 kg of fertilizer N was applied as a side dress at planting. The CRC and TRC systems were planted at 78,450 and 96,800 plants ha^-1, respectively. A conventional 30" row spacing was used in the case of CRC and a twin row 7" apart and centred on a 30" spacing was used for the TRC system. Cumulative denitrification losses during the 2013 growing season (GS) were not significantly different, amounting to 25.2 and 18.5 kg N ha^-1 for the CRC and TRC systems, respectively. Nitrogen leaching losses via tile drainage during the same period amounted to 15.9 and 16.9 kg N ha^-1 for CRC and TRC, respectively. Subsequent nitrate leaching losses during the 2013-14 non-growing season (NGS) amounted 22.0 and 21.5 kg N ha^-1, respectively. Leaching losses were not significantly influenced in either period by cropping system. Silage yields of 28.3 and 32.5 metric tons ha^-1 for the CRC and TRC systems with N removals of 107.6 and 102.5 kg N ha^-1, respectively were also not significantly different. Placement and relative availability of side dress N fertilizer in the two systems may have been a complicating factor in evaluating N usage efficiency and will have to be addressed in subsequent growing seasons. Further evaluation of these systems is required before conclusions can be drawn.