Seasonal and crop rotational effects of manure management on nitrate-nitrogen leaching in Nova Scotia

High nitrate-nitrogen (NO₃-N) concentrations and loads in tile drainage waters in response to crop fertility and other land management practices are a major cause of concern to the health of humans, animals and the environment. The study, conducted at Kentville, Nova Scotia (NS), examined the effect of renovating fallowed land with the introduction of either manure amended permanent forage (PF) or manure amended corn (Zea mays L.) - soybean (Glycine max L.) - wheat (Triticum aestivum L.) Corn-soybean-wheat (CSW) rotations on growing season (GS) and non-growing season (NGS) nitrate (NO₃-N) concentrations and loads of tile drainage water. Treatments included (i) PF rotation established with conventional tillage (CT) practices; (ii) CSW-CT rotation; (iii) minimum tillage in a CSW rotation (CSW-MT) and (iv) zero tillage in a CSW rotation (CSW-ZT). NGS drainage was significantly higher and flow-weighted NO₃-N concentrations significantly lower in all years when compared with GS. There were no consistent differences observed in GS or NGS NO₃-N concentrations and loads between the three levels of tillage in the CSW rotation with loads ranging between 7.1 and 28.2kgNL⁻¹ and 18.7 and 77.0kgNL⁻¹ for GS and NGS, respectively. PF rotation was significantly more efficient in N utilization when compared with a CSW rotation, resulting in significantly lower loads. Decreasing nitrate loads over time appeared to be related to increasing evapo-transpiration and N uptake as the forage matured. Although differences in the amount of N removed by corn, soybean and spring wheat in the CSW rotation were observed, these were not significant in determining the magnitude of NO₃-N loads. The correlation between LDM application and NO₃-N losses in tile water under this rotation in a particular season proved difficult to define. The study showed that the biological response time of the manured, soil system for NO₃-N loading is longer than one seasonal cycle and demonstrates the need to evaluate the long-term impacts of these rotations.