- Malheur Experiment Station
Tilling is the practice of aerating the soil to permit moisture and air to permeate, allowing seeds to germinate, encouraging root growth, controlling weed growth, and integrating fertilizers into the soil. One field may be tilled multiple times before planting for different reasons. Land without a history of recent annual crops is often tough and needs to be tilled to prepare it for planting. Primary tilling is done to uproot weeds and tough stubble, while secondary tilling makes the soil finer. The removal of weeds prevents them from going to seed (Manitoba), while stubble removal helps control some diseases by reducing the pathogen’s ability to overwinter in a field ( Anderson, 2009).
Soil drainage is an important concern when growing onions because excess moisture in the soil will cause bulbs to rot
(Schwartz). Land should be plowed as deep as possible to facilitate drainage. Onions also have shallow root systems with little ability to penetrate dense soil, and the loose, tilled soil helps to promote easier root growth (Weaver), and
(Riofrio). Fertilizing the beds prior to planting can promote early root growth and development.
Excessive tillage can harm soil structure. Tillage of silt loam soil while wet increases soil bulk, density and has lasting negative effects on productivity.
While conventional tillage is helpful for plant growth, it can also lead to erosion and loss of nutrients. Conventional tillage can be combined with more sustainable practices to help offset these losses. Polyacrylamide (PAM) and mulching in furrows can help reduce offsite loss of soil and nutrients. Mulching can sometimes be cost prohibitive, but has the benefit of adding organic material to the soil at the end of the season when tilled under, and has even been shown to reduce emergence of Thrips (Larentzaki, Plate, Nault, and Sheldon, 2008) and improve yield.
Adjustments can also be made to irrigation systems to reduce erosion and loss of nutrients. A sediment pond or a series of ponds can be added to the bottom of a furrow irrigated field to collect runoff water and eroded sediment and nutrients. This sediment can be dug out at the end of the season and put back on the field to conserve topsoil. Additionally, a tailwater recovery system can be added to sediment ponds to not only catch eroded sediment and runoff water, but to recycle irrigation water for further use. Such a system is ideal when water quantity conservation is a high priority.
Finally, alternative irrigation systems could be used to reduce erosion and runoff. Drip irrigation systems have the potential to increase yields and profits while reducing erosion and nutrient loss. However, A drip irrigation system can have a high initial cost, but brings water directly to the root zone of the crop. There are also a number of different sprinkler systems that could be utilized including pivots, wheel lines, hand lines, and solid sets. However, onion yields under sprinkler systems have been lower in Malheur County, suggesting that sprinklers may no be a cost effective alternative at this time.