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Fluid Journal : Winter 2017
10 The Fluid Journal Winter 2017 improving nutrient use efficiency. Work plan Site,cultural practices. Experiments were conducted at Champaign, IL using adjacent plots maintained in a corn- soybean rotation. The fertigation plots are situated on a Drummer Flanagan soil (silt loam, 3.6% organic matter, 21.1 meq/100g CEC, 5.8 pH, 22 ppm P, 99 ppm K, and 9.5 ppm S using Mehlich-3 extraction) that is tile drained. The subsurface drip irrigation (SDI) fertigation system was installed in the spring of 2014 and consists of 48 equally sized zones that can be regulated for differential application of irrigation and fertigation. Using programmable controllers, each zone can precisely supply varying rates of nutrients at specific growth stages, according to plant needs.The dripper lines are buried approximately 14 to 16 inches below the soil surface with 30-inch spacing between lines. The SDI system covers ten acres total, divided equally between corn and soybeans. Plots were maintained weed- and disease-free. Research approach. Five corn hybrids (Channel 214-45 STX-RIB, Croplan 7087 VT2P, DeKalb C61-54SS, DeKalb C64-87SS, and NK74R-3000GT) were planted on 28 April 2015. Using a precision plot planter (SeedPro 360, ALMACO, Nevada, IA), four population densities were evaluated (32,000, 38,000, 44,000, and 50,000 plants per acre). Corn plots were four rows wide and 37.5 feet in length with 30-inch row spacing. For soybeans, 17 varieties were evaluated, representing four different seed brands (Asgrow, Hi-Soy, Syngenta, and Croplan) and maturity groups, ranging from 2.9 to 3.8 (AG2935, AG 2933, AG3634, AG3832, HS31A32, HS39A42, S25-L9, SA28-D3, S30-V6, S35-A5, S37-Z8, R2T2501, R2C2674, R2C3113, R2C3323, R2C3783, R2C3800). These were planted on 15 May 2015 to achieve a final population of approximately 160,000 plants/acre in two-row plots 17.5 feet in length with 30-inch row spacing. The influence of foliar protection was evaluated by applying both an insecticide (Fastac TM EC; alphacypermethrin) and fungicide (Priaxor TM; fluxapyroxad + pyraclostrobin) at the R3 stage (20 July 2015) at a rate of 4 oz per acre, each using a backpack sprayer, while comparing to unsprayed plots. Nutrient scheduling. Irrigation was applied at soil water capacity of 40% to 60%, according to soil probes. When natural precipitation was adequate for crop growth and development, water was applied only as a medium for the fertigation component of this study. Soluble nutrient sources were used with a low ability to form precipitates in solution (e.g. urea ammonium nitrate, ammonium polyphosphate, ammonium thiosulfate, etc.). During periods of fertigation, a non-continuous (bulk) application of nutrients was applied during specific developmental stages (Tables 2 and 3). An equal parts application technique was used in which 1) the system is brought to full pressure with water (for 1 hour), 2) nutrients are injected and applied (for 1 hour), and then 3) the system is allowed to rinse with only irrigation water (for 1 hour). Using the values and the timing at which nutrients were acquired in a non- irrigated environment from Bender et al. (2013), a seasonal fertigation design was used to supply corn with an additional 113 lbs N, 120 lbs P2O5, 150 lbs K2O, 12 lbs S, and 16 oz Zn/acre during seven fertigation periods between V5 to R5 in addition to a standard application of 180 lbs N/acre as urea at planting (Table 2). The control irrigation treatment also received 180 lbs N/acre at planting. The schedule for soybean nutrient fertigation was based largely upon soybean nutrient uptake curves (Bender et al., 2015) and recommendations for soybean fertigation by Bar (2004). A total of 75 lbs N, 55 lbs P2O5, 150 lbs K2O, 25 lbs S and 18 oz Zn per acre was applied through fertigation. Nitrogen fertigation included an early starter application with an additional 50 lbs N supplied to assist grain development during seed filling. Supply of other macronutrients, including P and K, was by incremental applications Table 9. Soybean yield response to fertigation and foliar protection at Champaign, IL in 2015. Values are the average of 17 commercial soybean varieties with relative maturities ranging from 2.5 to 3.9 and four replications. Fertigated plants received 75-55-150-25S-1Zn (lbs/ acre) compared to irrigated plants. Foliar protection included an insecticide and fungicide applied at the R3 growth stage. System Foliar Protection Average Range ---------- bushels Ac-1 ---------- Irrigated None 70.5 57–80 Irrigated Foliar Protection 74.7 59–83 Fertigation None 78.6 68–85 Fertigation Foliar Protection 80.6 70–89 * Least significant difference (P ≤ 0.10) for foliar protection within a culture system is 0.75. Table 10. The interaction of fertigation, foliar protection, and relative maturity on soybean yield grown at Champaign, IL with four replications. Fertigated plants received 75-55-150-25S-1Zn (lbs/ acre) compared to irrigated plants. Foliar protection included an insecticide and fungicide applied at the R3 growth stage. Variety (Relative Maturity) System Foliar Protection S25-L9 (2.5) S28-D3 (2.8) S30-V6 (3.0) S35-A5 (3.5) S37-Z8 (3.7) ------------------------------------- bushels Ac-1 --------------------------------- Irrigated None 59.3 57.8 67 75.6 72.6 Irrigated Foliar Protection 59.1 67.8 70.9 82.4 78.9 Fertigation None 70.1 74.8 68.7 83.1 76.4 Fertigation Foliar Protection 72.7 78.4 69.5 89 80.1 * Least significant difference (P ≤ 0.10) for variety, irrigation by variety, and foliar protection are 2.9, 7.2, and 0.75, respectively.