The results of two years of research (two trial locations per year) on effect of applied nitrogen on garlic yield are summarized in this article. Different rates of spring-applied nitrogen and seed size are taken into consideration, as well as plant tissue and soil analyses for nitrogen. In eight side-by-side comparisons, we never saw a yield response between 50, 100 and 150 lb/A of applied nitrogen.
50 lb/A is all that was needed!
In 100% of eight side-by-side comparisons, there were no differences in yield among 50 lb/A, 100 lb/A and 150 lb/A of spring-applied inorganic nitrogen in German hard neck garlic. Trials encompassed two years of trials (2017, 2018), three trial sites, three planting configurations, three types of inorganic nitrogen fertilizer, three fertilizer application techniques, and different seed sources and sizes. In the second year of study, 50 lb/A of spring-applied nitrogen significantly increased yield by 20% compared to 0 lb/A applied nitrogen. These results suggest that garlic only needs 50 lb/A of nitrogen to be available in the spring when the crop begins to grow.
This seems low! University recommendations state that garlic needs between 150 and 175 lb/A nitrogen. So, why did we NEVER see a yield response with greater than 50 lb/A of applied nitrogen? In Western NY, the garlic trials followed sod (Batavia 2017) and oat cover crop (Albion 2018). Additionally, liquid dairy manure was applied in the fall at the Albion site. The increased organic matter made available by turning in sod/cover crop and the manure application in western NY provided an unmeasured credit, which should be factored in. The Long Island site, however, only has about 2% organic matter, so should only receive a maximum nitrogen credit of 15 lbs/percent organic matter, or 30 lbs. If we use trial planting configuration to calculate yield per acre, actual laboratory results for % N in bulb tissue at harvest (Albion 2018 data), and assume that the bulbs are 36% dry matter, we can crudely estimate the amount of nitrogen taken up by the garlic bulbs harvested in our trial, which was roughly 55 to 85 lb/A. This does not include the amount of N that would have been left in the field in the foliage at the end of the season. Interestingly, the amount of available nitrate-nitrogen (NO3-N) left in the soil at harvest in the Albion trial in 2018 (only time this data was collected) was 6, 22, 38 and 76 lb/A for the 0, 50, 100 and 150 lb/A rates of applied N, respectively (data not shown). These results are another indication that the garlic in these trials had taken up all of the nitrogen that they needed and that excessive nitrogen was applied.