Nitrogen Application Methods and Timing for Corn after Soybean in a Ridge-Tillage System

Nitrogen placement options for improved N efficiency are limited in ridge-tillage systems where primary and secondary tillage for fertilizer incorporation is absent. Studies were conducted for 3 yr on a Webster clay loam (fine-loamy, mixed, mesic Typic Haplaquoll) in southern Minnesota to determine the effect of placement and time of N application on corn (Zea mays L.) production and postharvest residual soil nitrate (RSN) and to evaluate the spoke-wheel injector for precise placement of urea-ammonium nitrate solution (UAN, 28-0-0) for corn after soybean [Glycine max (L.) Merr.] in a ridge-tillage system. Nitrogen as UAN was either band-applied on the ridge, broadcast, or point injected into the ridge (PINJ-R) or valley (PINJ-V) and was compared with anhydrous ammonia (AA) injected into the valley (INJ-V). Single preplant and pre-emergence applications were compared with split applications where 30 to 40% was applied preemergence and 60 to 70% was applied at the V7 and V16 growth stages. Leaf N concentration at the Rl stage and whole plant dry matter and N concentration at the R2 stage were generally enhanced by single preemergence applications compared with split applications and by PINJ-R compared with the PINJ-V treatment. Grain yield, total N uptake, and net economic return were generally optimized by point injecting UAN and the injection of preplant AA compared with band and broadcast applications of UAN. Split applications did not produce higher yields, N uptake, or net economic return than single preemergence injected applications of N. However, RSN was highest with the V16 application of UAN under these nonirrigated conditions. Three-year average grain yield and net economic return were highest with the preemergence PINJ-R treatment. These results suggest that a single preemergence spoke-wheel application of UAN into the ridge or preplant AA in the valleys can be successfully used to optimize N management and corn production following soybean in a ridge-tillage system. Nitrogen efficiency will be enhanced and ammonia volatilization will be reduced with these application methods. Research QuestionEconomically profitable and environmentally sound corn production in conservation tillage systems requires excellent N management. Placement options are often limited, however, if no primary or secondary tillage is conducted. The objectives of this study were to: (i) determine the effect of placement and time of N application on corn production and residual soil nitrate (RSN) levels, (ii) evaluate band vs. broadcast and single vs. split applications of N, and (iii) evaluate the spoke-wheel injector as a tool for precise placement of urea-ammonium nitrate (UAN) solution for corn following soybean in a ridge-tillage system. Literature SummaryMany studies have cited reduced corn yields and significant volatilization losses of ammonia when urea containing fertilizers, e.g. UAN, are applied to the soil surface and not incorporated in conservation tillage systems. These negative effects are most prevalent in no-till continuous corn, but also occur in other tillage systems where incorporation is not practiced. The spoke-wheel injector developed in the late 1980s in Iowa gives greater timing and placement flexibility for N application in conservation tillage systems. Few studies have compared a wide range of N application methods and timing options, especially for corn after soybean in a ridge-tillage system. Study DescriptionA 3-yr study was conducted on a Webster clay loam at the University of Minnesota Southern Experiment Station at Waseca. Nitrogen as UAN was either band-applied on the ridge, broadcast, or point injected into the ridge (PINJ-R) or valley (PINJ-V) and was compared with anhydrous ammonia (AA) injected in the valleys. Single preplant and preemergence applications were compared with split applications where 30 to 40% of the N was applied preemergence and 60 to 70% was applied at the V7 and V16 growth stages. Leaf N at silking, whole plant dry matter and N concentration at the blister stage, grain yield, total N uptake, and RSN measurements were taken each year to evaluate the treatments. Applied QuestionsWere corn grain yields and net economic return to N affected by N placement? Highest yield and net economic return were obtained with the PINJ-R treatment and were followed closely by preplant AA and preemergence PINJ-V when applied at the 100-lb N rate (Table 1). Surface application of UAN either in an 8 to 10-in. band on the row or broadcast resulted in slightly lower yields, N uptake, and net economic return. Were corn grain yields and net economic return to N affected by timing of N application? Split applications consisting of 30 to 40 lb N/acre band-applied preemergence and sidedress applications of 60 to 70 lb N/acre as either AA or UAN at the V7 or V16 growth stages did not produce greater yields or net economic return to N than single, preemergence injected applications of N on this clay loam soil (Table 1). Applying a portion of the N at the V16 stage resulted in the greatest RSN values in the 0 to 3 ft. profile, thereby suggesting a greater potential for postharvest leaching of nitrate. Were mid-season leaf and whole-plant measurements helpful in assessing the end-of-season performance of the N application methods? Many of the placement and timing effects measured at the silking and blister stages did not occurr with respect to grain yield. Apparently, conditions in this corn-soybean system were conducive for some late-season uptake of N and corn growth after onset of the reproductive stage to offset many of the mid-season concerns. Was the spoke-wheel injector an acceptable tool for applying UAN to this conservation tillage system? The spoke-wheel injector performed well and offered great flexibility in the timing and placement of UAN. Corn plants were not damaged. High N-use-effciency was obtained with this application method. Based on our experiences, the spoke-wheel injector should perform satisfactorily in a variety of tillage systems. RecommendationsNitrogen management and corn production after soybean can be optimized by a single preemergence, spoke-injection of UAN directly into the ridge or preplant AA in a ridge-tillage system. These application methods will enhance N eficiency and reduce ammonia volatilization commonly found with nonincorporated, surface application of UAN. Table 1Three-yr average corn grain yield and net economic return to N as influenced bv N rate, source, and amdieation time and method. NitrogenApplicationNetGraineconomicRate†Source‡Time§Methof¶yieldreturn to NlbN/acrelb/acre$/acre0Control----114.9--100AAPPINJ-V154.784 60UANPEB-R138.143100UANPEB-R150.866140UANPEB-R160.681100UANPEBDCT147.758100UANPEPINJ-R161.494100UANPEPINJ-V155.37730 + 70UAN/AAPE + SD (V7)B-R/INJ-V155.37730 + 70UAN/UANPE + SD (V7)B-R/PINJ-V153.46430 + 70UAN/UANPE + SD (V16)B-R/PINJ-V153.46430 + 50UAN/UANPE + SD(V16)B-R/PINJ-V148.757†30 + 70 = 30 lb preemergence + 70 lb sidedress and 30 + 50 = 30 lb preemergence + 50 lb sidedress in 1986. Rates were changed to 40 + 60 and 40 + 40, respectively, in 1987 and 1989. ‡AA = anhydrous ammonia; UAN = urea-ammonium nitrate. §PP = preplant; PE = preemergence; PE + SD V7 = preemergence + sidedress at V7 stage; PE + SD VI6 = preemergence + sidedress at V16 stage. ¶INJ-V = injected in valley; B-R = band sprayed on ridge; BDCT = broadcast sprayed; PINJ-R = point injected in ridge; PINJ-V = point injected in valley.