Effects of In-season Fertilizer Strategies on the Yield and Nitrogen Use Efficiency of Irrigated Corn PDF Download

Author: Alexander Soroka
Publisher:
ISBN: 9781369353426
Category :
Languages : en
Pages : 113

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Book Description
Inefficient use of nitrogen (N) fertilizer in agronomic crop production can lead to water quality concerns and reduced yields for growers. Nitrogen left in the soil after crop harvest is subject to leaching losses to groundwater or gaseous losses to the atmosphere. Split additions of N via sidedressing or fertigation can better time N applications with corn N uptake and improve N use efficiency (NUE). Irrigation can also stabilize yields and raise NUE at decade time scales. The objectives of this study were to 1) quantify the effect of N rate and timing under central pivot irrigation on grain yield and N use efficiency in Delaware using a plot study and 2) investigate the impact of irrigation on yield and NUE in Delaware using historical yield data. A plot study was completed by establishing irrigated corn on well-drained soil which received zero N (control) or 6.72 Mg ha-1 poultry litter, 34 kg ha-1 starter N at planting, and 0, 82, 140, or 198 kg ha-1 of in-season N (applied at sidedress at V5 or via fertigation at V5, V8, V11, and V13). Grain yield was determined for each treatment at harvest using a weigh wagon. Pre-plant soil, post-harvest grain, residue, and in-season soil samples were collected and analyzed to allow calculation of NUE by several methods. Nitrogen application rate affected yields and NUE more than N timing and application when in-season N was applied. Yields of irrigated corn were statistically similar at N rates exceeding 82 kg ha-1; average yields over the study period were 17 Mg ha-1. Partial factor productivity of nitrogen was above 60 kg kg-1 for corn at all N rates except the highest rate. Total aboveground biomass for irrigated corn treatments receiving supplemental N generally contained more N in plant tissue (values ranged from 214 to 254 kg ha-1) than Chesapeake Bay Model Scenario Builder (SB) maximum uptake estimates of 218 kg ha-1. Mass balance estimates of NUE indicated that 13 to 49% of available N applied to plots could not be unaccounted for in plant tissue or soils. The mass balance approach illustrated a trend for increasing unaccounted for N with increasing N rate but, this was only significant in 2014. Leachate concentrations of NO3-N at 60 cm depth were highest in plots receiving supplemental N, with mean concentrations of 7 and 22 mg L-1 NO3-N in 2014 and 2015, respectively. Currently, irrigated land receives an interim credit of 4% reduction in total N in the Chesapeake Bay Model. This reduction is modeled like a filter, where irrigated corn would release 4% less N than comparable rainfed fields. Historical data from University of Delaware corn hybrid variety trials were analyzed to evaluate effects of irrigation on corn yields and NUE over time. Historical yield data and calculated NUE (from variety trials and UD field plot studies) were compared to values in the literature and those used by the Chesapeake Bay Program. In the last two decades, hybrid variety trials met and exceeded the 12.5 Mg ha-1 yield maximum value used in the Chesapeake Bay Model SB. Rainfed plots were 80 and 85% as efficient as irrigated plots in converting applied N to grain yield over the 35 year history of UD corn variety trials. A scenario indicated that irrigated corn could consume 1,030 Mg more N annually than rainfed plots if they were fertilized based on UD N rates for a realistic irrigated yield goal. Based on results of a two-year plot study at UD Warrington Irrigation Farm and analysis of 35 years of yield data from UD variety trials, we make the following preliminary recommendations: 1) lower UD N rate recommendations for high yielding irrigated corn by 15 % to account for increased NUE of irrigated corn and 2) Evaluate if irrigation's NUE would be more appropriately modeled as a separate crop category or, as a BMP. Future research should focus providing data to further refine these recommendations by quantifying NUE at a regional scale. On-farm strip trials could be conducted by UD researchers with a common protocol at multiple locations to evaluate how NUE and yields are affected by irrigation and N management. In addition, we also recommend collection and analysis of leachate and groundwater samples as part of these strip trials to determine risk of N losses at different locations under various soil and management conditions.