Soil quality indicators and economic feasibility of two organic, reduced tillage crop rotations in the Palouse region

Background/Question/Methods

Organic, reduced till (ORT) dryland cropping systems have the potential to reduce soil erosion and improve soil quality in the hilly, highly erodible Palouse region of northern Idaho and western Washington.  The influence of ORT systems on soil quality parameters such as earthworm density and biomass, soil organic carbon (SOC) and aggregate stability has been little studied.  Furthermore, the economic feasibility of these systems is not clear.  To investigate the significance of ORT crop rotations on soil quality parameters and yield, we are measuring earthworm density and biomass, aggregate stability, hydraulic conductivity, bulk density and SOC in replicated plots allocated to two ORT cropping systems (wheat-green manure vs. alfalfa-wheat) and one non-organic reduced-till system.  Earthworm populations have been measured annually (2010-2013) and changes in soil physical properties and SOC will be assessed following six years of ORT rotations.  Enterprise budgets for organic winter wheat and winter pea will complement the existing budgets for alfalfa in order to evaluate the feasibility of these systems for the Palouse.

Results/Conclusions

In 2010, there was a non-significant trend for greater earthworm density in the organic alfalfa-wheat rotation (68 individuals m^-2), and lower densities of 31 and 25 individuals m^-2 in the organic and non-organic wheat-green manure rotations, respectively. Earthworm density has increased in the organic treatments, with a mean value of 111 individuals m^-2 in 2012.  The organic wheat-green manure system has produced similar or higher yields than the non-organic comparison. In 2010, for example, winter wheat yields were 81bu ac^-1 in the organic wheat-green manure rotation and 59 bu ac^-1 in the non-organic wheat-green manure system, perhaps due to benefits of enhanced earthworm activity, organic fertilizer (quail manure) or higher yields of the preceding winter pea crop in the organic system (1,180 lbs ac^-1) as compared to the non-organic rotation (1,011 lbs ac^-1). Spring wheat yields in 2011 were similar between the organic (38 bu ac^-1) and non-organic (42 bu ac^-1) rotations. Overall, the data suggest that ORT rotations may promote earthworm activity and increase or maintain yields. The influence of rotation and earthworm density on soil physical properties and the economic performance of each system are currently being investigated and will be discussed in detail.