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Fluid Journal : Winter 2016
previous study, but in a non-irrigated environment. Using this information, a seasonal fertigation schedule was used to supply 80 Ibs N, 70 Ibs K 2 0 and 14 Ibs S per acre during seven fertigation periods between V6 to R2 for the fertigation treatment, in addition to a standard application of 180 Ibs N/A as urea at V4 broadcasted across all treatments. The schedule of nutrient fertigation in soybeans was based largely upon nutrient uptake patterns (Bender et al., 2015) and recommendations for soybean fertigation by Bar (2004). A total of 50 Ibs N, 76 Ibs K 2 0 and 16 Ibs S were applied per acre during six fertigation periods between V4 and R7. Applied K and S were split between the V4, V6, R2, and R4 growth stages in contrast to N, which was applied at R5 and R6. For both experiments, calculation of nutrient recovery efficiency (Eq. 1) was used to measure the proportion of applied nutrients recovered in above-ground biomass. Nutrient Recovery Efficiency = (Content F ) - (Content l ) X 100 Application Rate in which "ContentF" (Ibs/ A) corresponds to above-ground nutrient content of the fertigated treatment relative to the nutrient content of the irrigated control, "Contentl" (Ibs/ A) at a specific "Application Rate" (Ibs/ A). Parameters. Cumulative rainfall, irrigation events, and temperature data were collected throughout the season. At physiological maturity, above-ground whole plant biomass and nutrient accumulation were measured for each corn hybrid and a subset of soybean varieties to estimate the recovery efficiency of applied nutrients. The center two rows of each plot were mechanically harvested for grain yield. Results Weather. Environmental conditions during 2014 generally consisted of above-average precipitation with below- average temperatures with little weather- induced stress (Figure 1). As a result, record yields were recorded for soybeans and corn at the local, state, regional, and national levels. Limited in-season irrigation was necessary because of above-average rainfall during 2014 and therefore, irrigation was primarily used as a medium for fertigation in the 13 Table 6. Effect of fertigation treatment on R8 biomass accumulation and nutrient recovery for a subset of six soybean varieties grown at Champaign, IL during 2014. Based on yield results from Table 5, varieties were classified as yield 'responsive' or 'non-responsive' to the fertiga- tion regime and corresponding differences in biomass production were compared. A total of 50 Ib N, 76 Ib K 2 0, and 16 Ib S on a per acre basis were applied during six fertigation periods between V4 and R7. Recovery efficiency represents the percentage of total applied nutrients accumulated in above-ground biomass. Variety/ Irrigated Fertigated Difference Recovery Efficiency (oÆ>) Category Non-Re- ------ R8 Biomass (Ib Ac- 1 ) ------- N K S sponsive R2C3113 7162 7492 329 20 21* 3 R2C3822 8211 8114 -96 10 21* 8 S32-L8 7471 7473 2 3 -4 1 S39-U2 8084 8020 -64 14 -26* 9 Average 7733 7774 43 12 3 5 Responsive AG3634 7117 7436 319 26 11 16* AG3832 7345 7848 503 44* 2 11* Average 7231 7642 411 * 35* 6 14* (*) Significantly different than zero at a=0.1 O. current studies. Despite the delayed planting of corn and soybean trials due to the construction of the SDI system, measured yield responses to fertigation and agronomic management provided critical insight regarding opportunities for improved nutrient management. Corn yield. Hybrid (P < 0.001), planting density (P = 0.004), and fertigation (P < 0.001) treatments significantly influenced grain yield. Overall, fertigation improved yield by an average of 20 bu/A across all treatments. Individual hybrids measured similar yield increases to fertigated nutrients, which ranged from +20 to +22 bu/A (Table 1). Responses to fertigation exhibited no relationship with yield or biomass levels (Table 2) measured in the control irrigation treatment, indicating that benefits from nutrient fertigation may be expected regardless of typical hybrid yield levels. Complementary agronomic practices necessary to maximize yield in a fertigated environment may also include greater planting densities. Previous studies by the University of Illinois Crop Physiology Laboratory characterized the evaluated hybrids as tolerant of high planting populations. As such, grain yields in the current study tended to increase with greater planting densities to a maximum yield level, and then decline with subsequent increases in plant population (Table 3). Under irrigated conditions, maximum yields were measured at 30,000 pi/A, contrary to treatments receiving fertigation, which The Fluid Journal were numerically greatest at 36,000 pi/A. Newer hybrids not only tolerate higher planting densities relative to historical germplasm (Tokatlidis and Koutroubas, 2004), but their increased nutrient recovery at higher populations (Boomsma et al., 2009) suggests that there's a greater necessity for nutrient management in these environments. Responses to fertigation were greatest at the 36,000 pl/A density, where a 26 bu/A (P < 0.10) increase in grain yield resulted from both greater plant biomass (Table 4) and a 2.8 0 /0 improvement in dry weight harvest index (data not shown). Biomass & nutrient recovery. Across all corn hybrids and planting densities, fertigation improved total biomass production at R6 by 1,515 Ibs/A and resulted in a net recovery of 45.4 0 /0 of N, 49.9 0 /0 of K, and 18.3 0 /0 of S (Table 2). Although fertigation similarly increased R6 biomass across hybrids, differences in total biomass influenced nutrient recovery efficiencies. Hybrid DKC62-08, for example, measured the least biomass accumulation and grain yield (Table 1), though it had the greatest recovery of applied nutrients (Table 2). Alternatively, DKC66-33 and N63R-3000GT measured greater biomass and grain yields with a general tendency for reduced nutrient uptake and greater nutrient use efficiency. These data highlight the contrasting response characteristics among elite germplasm and emphasize that hybrid selection is a critical decision that influences the response of many Winter 2016