When following an N-inefficient crop like potatoes or grown in high organic matter soils, carrots often require little or no fertilizer N. Ĭarrots are efficient at using residual and mineralized N. Sidedress applications of 60-80 lbs N/acre are common. Excess N applications and large N fluctuations should be avoided, as they can hurt carrot quality. In California, where average yield is around 300 cwt/acre, rates higher than 150 lbs N/acre aren't normally needed. Additional N contained in culls and tops can vary widely, and may add an additional 50% to 250% N, such that a 300 cwt/acre crop might require anywhere from 90 to 210 lbs N/acre of available N from all sources. More information on common fertilizer types can be found at the International Plant Nutrition Institute website.ĭata from carrot uptake trials around the world suggest that on average about 20 lbs N are removed for every 100 cwt of marketable roots. Contact your local farm advisor for more information. Since timing of N release depends on temperature and the thickness of the polymer coating, to ensure the timing of N availability matches the crop's demand it's important to choose a product that's suited to the crop, variety and climate. Yield improvements were greater at low N rates. The proportion of US#1 grade carrots was also increased. A study on a loamy soil in Arizona found that when polymer-coated urea was applied in a single preplant application, January-planted carrot yields were increased by an average of 64% compared with a split application of urea. However, benefits were not seen with all the slow-release products they tested. An experiment in Canada observed that a preplant application of a slow-release N fertilizer improved stand and marketable yields compared with a split application of UAN 32. Ĭarrots may benefit from products which release N slowly. Urea and diammonium phosphate (DAP) should be used with care, as they release ammonia, which can inhibit germination. More detailed instructions can be found here.įertilizers that contain both ammonium and P tend to facilitate crop uptake of both N and P. The nitrate concentration in the supernatant can be measured with nitrate-sensitive colorimetric test papers. The soil particles are allowed to settle until a clear supernatant forms. The tube is then capped and vigorously shaken for about 1 minute to disperse all the aggregates. Field moist soil is added until the extractant reaches the mark. įor the soil nitrate quick test, 30 mL of a calcium chloride (0.01 M) or an aluminum sulfate (0.025 M) solution are measured into a clean 2-oz bottle or a centrifuge tube with a mark at 40 mL. With the quick test, soil nitrate can be determined in a timely manner in order to make N fertilization decisions. Although the quick test is less accurate than a standard laboratory analysis, its accuracy is generally sufficient for routine on-farm use when done correctly. The soil nitrate quick test with colorimetric test strips is highly correlated with the standard laboratory technique and has been found to be a reliable estimate of current soil N status. Soil samples can be sent to a laboratory or extracted and analyzed on the farm.
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