Nitrate leaching as influenced by cover crops in large soil monoliths

Unacceptable levels of NO3 leaching to ground water and drainage systems can occur under corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotations. Cover crops have the potential to reduce NO3 leaching, but this process has not been well documented. Lysimeters utilizing large soil monoliths are an excellent approach for studying NO3 leaching because inputs can be controlled and outputs accurately measured. The objective of this study was to see if fall cover crops could reduce NO3 leaching from large soil monoliths. We used three (1 by 1 by 1.5 m deep) monoliths in each of two controlled climate chambers with oat (Avena sativa L.) or rye (Secale cereale L.) fall cover crop interplanted into soybean in mid-August. The study was continued for two cover crop cycles in each chamber. In Chamber 1, drainage was significantly reduced due to oat or rye cover crops for the fall through summer of Years 1 and 2 (first cover crop cycle), and NO3 loss was reduced for most of the same time period. In Chamber 2, NO3 loss was reduced for the spring-summer season of the second year (first cover crop cycle). Although drainage was less under cover crops for Chamber 1, the soil water content was not consistently lower because of replenishment by watering. The soil monoliths were useful for showing that oat and rye cover crops in a corn-soybean rotation can reduce NO3 leaching from lysimeters and suggest that the same trend would be true in tire field.