How much will reduced tillage and alternative crop rotations reduce runoff and sediment generations in a potato production system in Atlantic Canada?

Potato is the main cash crop in Atlantic Canda. Potato cropping is associated with intensive tillage and high levels of fertilizer and pest inputs. Frequent soil disturbance, together with the rolling landscape and loamy soils, has resulted in high levels of water erosion in this region. In order to reduce the water erosion risks, efforts have been made to adopt Beneficial Management Practices (BMPs) such as reduced tillage and alternative crop rotations with agro-ecological considerations. However, there is no field study to quantify the effectiveness of these BMPs. To fill this knowledge gap, rainfall simulation experiments were conducted to measure runoff and sediment generations in three crop rotations under two types of tillage. The three crop rotations examined were: the conventional Potato (PO)-Barley (BL)-Potato (POBLPO, used as the control), Corn (CO)-Spring wheat mixed with Triple mix (WT)-Potato (COWTPO) and Corn mixed with Ryegrass (CR)- Wheat mixed with Alfalfa and timothy (WA)-Potato (CRWAPO). The two types of tillage are conventional tillage (CT, used as the control) and reduced tillage (RT). A mini rainfall simulator was used to simulate 20 minutes rainfall. Runoff samples were collected every minute from which the runoff flow rate, sediment export rate and sediment concentration at every minute were determined. Cumulative measures such as runoff discharge, sediment yield and Flow-Weighted Mean Sediment Concentration (FWMSC) were calculated for 5, 10, 15 and 20 minutes durations of simulated rainfall.

The results overall demonstrate the strong effects of tillage and crop rotation on runoff and sediment generations although there were some exceptions. In the cash crop year, compared to CT, RT increased runoff discharge for short durations of rainfall but reduced it slightly for long durations of rainfall. For PO, RT only reduced sediment yield and FWMSC slightly but for CO and CR, sediment yield and FWMSC reductions by RT were more than 100 times. Compared to PO, CO and CR significantly reduced runoff discharge,  sediment yield and FWMSC. In particular, the reductions of sediment yield and FWMSC from PO to CO and CR under RT were more than 100 times. In the rotational crop year, compared to CT, RT reduced runoff discharge mostly by more than one third and reduced sediment yield and FWMSC by more than ten times. Compared to BL, WT and WA mostly reduced runoff discharge and sediment yield but the reductions were small. Based on these results, it was estimated that by switching from the conventional crop rotation (POBLPO) with conventional tillage to the alternative crop rotations (COWTPO and CRWAPO) with reduced tillage, runoff discharge, sediment yield and FWMSC on average will be reduced by 13 %, 59 % and 69 %, respectively.