Growing onions in a minimum tillage system would drastically reduce the negative economic and environmental consequences of erosion, while sustaining long-term production of onions grown on muck soils. A study conducted in 2008 showed that a minimum tillage systems using fall-planted winter wheat and spring oats as inter-row cover crops in direct seeded onions had a lot of promise. In this project, critical improvements to these systems necessary for grower adoption were studied. A 1.5-fold increase in the rate of spring barley to 75 lbs/acre (in place of oats) planted in the fall resulted in a 3- and 5-fold increase in ground cover and cover crop residue, respectively, and thus, acceptable protection from soil erosion.
Instead of applying phosphorous and potassium in the fall prior to seeding the cover crops and relying on side-dressing nitrogen during the spring as was done in 2008, in this study, applying NPK in the spring, followed by shallow incorporation with a multivator between the cover crop rows proved to be very effective. Growing onions in a minimum tillage system with a spring barley inter-row cover crop resulted in an above average yield of 509 and 492 cwt/A for Festival and Safrane varieties, respectively, and with 79% and 97% of the total weight falling into the higher priced medium and jumbo size bulb classes, the barley minimum tillage system had the highest economic return.
The cost of establishing this minimum tillage system was only two-thirds the cost of establishing onions conventionally, and required 3 fewer passes across the field. This study proved that when winter wheat was used as an inter-row cover crop that the resulting stand reduction was caused by either allelopathy or another crop inhibition mechanism, and that it was not caused by damping off pathogens. Consequently, spring-killed winter wheat should not be used as an inter-row cover crop in a minimum tillage system for direct seeded onions grown on muck soil.
Available nitrogen ranged from 1.4- to 5-fold higher in the minimum tillage systems throughout the growing season. The decomposing cover crops mineralized an estimated 20 to 25 lb/A of nitrogen, some of which became available to the onion crop during the season. The shallow depth of fertilizer incorporation of NPK in the minimum tillage systems also appeared to increase nutrient availability. Thus, there seems to be potential to reduce fertilizer rates when onions are grown in a minimum tillage system, the dynamics of which warrant further study. It appears that growing direct seeded onions in a minimum tillage systems with a spring barley inter-row cover crop on muck soil is a viable practice that growers can adopt to preserve nonrenewable muck soils and to reduce environmental pollution.
We observed three onion farmers who have adopted minimum till in muck soils and who have reduced their fertilizer rates. They have seen decreased disease and increased yields.
Results have been presented in Michigan at the Great Lakes Fruit, Vegetable and Farm Markets Expo, December 2012, an article was published in “The Grower”, and this project was featured in the national 2011-1012 SARE Report from the Field.
The purpose of this project was to continue our progress towards developing a minimum tillage system for direct seeded onions grown on muck soil. Specifically, our objectives were to:
This objective was partially met. Our goal was to achieve approximately 50% ground cover with both a fall and a spring-killed cover crop by mid-May. Although we had less than 50% ground cover for both fall and spring-killed cover crops, we had more uniform coverage between the two cover crops (fall – 19%; spring – 25%) than we did in the first year of study (fall – 10%; spring – 60%).
This objective was partially met. Timing of fertilizer application and incorporation in the spring was completed successfully and proved to be a successful and practical technique. Our plan was to evaluate three tillage systems in three varieties, but due to an abnormally wet and cold April and May in 2011, the stand establishment in the third variety was only 25%, so it was abandoned. We also set up a small-scale small-plot trial to investigate banding P and K below the seed. Unfortunately, applying fertilizer in a band below the seed proved impossible with our modified push seeder, because with minimum tillage the ground was simply too hard to push the seeder through the soil. Instead, a reduced fertilizer rate study was set up with 50%, 75% and 100% of the recommended rates of NPK. Again, due to an abnormally very wet and cold spring, we had very poor stand establishment (~33%) in this trial, and it too, had to be abandoned. Although we got some interesting results pertaining to the dynamics of nutrient availability when using inter-row cover crops, further study is warranted to understand this completely.
This objective was partially met. A small-plot trial was successfully established within the MT wheat system where damping off pressure was expected to be the highest to evaluate fungicide seed treatments to control damping off. We got no significant differences among treatments. Instead, we were able to conclude that damping off was in fact not the cause of reduced stand in the MT wheat system. Rather, our results strongly suggest that the use of a spring-killed winter wheat inter-row cover crop has either allelopathic or other crop inhibition effects on onion germination.