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Fluid Journal : Winter 2017
11 The Fluid Journal Winter 2017 Below is a Professor, Beyrer is a Research Specialist, Mastrodomenica is a Graduate Student and Seebaeur is a Sr. Research Specialist in the Department of Crop Sciences, University of Illinois, Urbana, IL. throughout vegetative and reproductive growth (Table 3). Measured parameters. Soil samples were obtained from plot areas prior to planting to confirm that fertility levels are uniform across the site. Daily air and soil temperatures, precipitation, irrigation, and soil moisture were monitored throughout the growing season. At physiological maturity, whole corn plant biomass and nutrient accumulation were measured from six-plant sub-samples to estimate the recovery efficiency of applied nutrients. Plant nutrient levels were analyzed by A & L Great Lakes Laboratories, Inc. (Fort Wayne, IN) and by Ward Laboratories, Inc. (Kearney, NE). Yield for corn was obtained using a plot combine on the center two rows of each plot, and adjusted to 15% grain moisture concentration. For soybeans, yield was obtained from both rows of the plot and adjusted to 13% grain moisture concentration. Experimental units were arranged in a split-plot RCB design: for corn with six blocks and for soybeans with four blocks. For both crops, the main plot was an irrigation system with two levels: irrigated and fertigated. In corn, the split plot was population, while for soybeans it was foliar protection, with hybrid/variety randomly assigned within each treatment block. Hybrid/variety, irrigation system, and population/foliar protection were considered fixed effects, while block and interactions with blocks were considered random effects. Measured parameters were analyzed using the PROC MIXED procedure of SAS (Version 8, SAS Institute, Cary, NC) and means were separated using Fisher’s protected LSD test at the 0.10 level of significance. Results Weather. Environmental conditions during 2015 generally were warm and wet in the spring to early summer, and drier and cooler the remainder of the season, with little other weather- induced stress (Table 4). As a result, record yields were recorded for corn and soybeans at the local, state, regional, and/or national levels. Consequently, irrigation water was only required during the reproductive stages of both corn and soybeans (Table 5). Irrigated fields in 2015 produced similar yields to dryland fields (data not shown). Corn fertigation. When averaged over the five corn hybrids, and four plant populations, the irrigated treatment produced yields of 194 bu/acre (Table 6). This is slightly less than the countywide average for 2015 of 216 bu/acre, possibly due to this SDI-fertigation system being installed the previous year and disturbing the soil, or due to hybrid selection. Fertigation significantly increased corn yields by approximately 52 bu/acre (27%), regardless of population (Table 6). While there was a trend for greater corn yields with increasing population in the irrigated treatment, fertigation maximized yields even at the lowest planting population (Table 6). Fertigation increased individual corn hybrid yields by 34 to 69 bu/acre, equivalent to yield boosts of 17% to almost 40% when averaged over all planting populations (Table 7). This finding may indicate that some hybrids are more suited to fertigation and can take advantage of the increased nutrient supply to produce greater yields. The increased yield in fertigated corn corresponded to an increase in the accumulation of the fertigated nutrients (Table 8). We calculated nutrient recovery as the increase in plant content of the fertigated plants minus the nutrient amount in irrigated plants divided by the amount of the nutrient supplied by fertigation. Nutrients are taken up preferentially, with 65% of the fertigated N accumulated, but only 25% of the fertigated P2O5 being accumulated. Complete (100%) fertigated nutrient recovery was not expected, as soil microorganisms also may accumulate these nutrients. However, further studies to determine the optimal timing or rate of these nutrients may be necessary to achieve the most efficient fertigation system. Soybean Fertigation. Fertigation significantly increased soybean yields by 8 bu/acre when averaged over all 17 varieties evaluated (Table 9). Adding foliar protection to either irrigated or fertigated soybeans boosted yields an additional 2 to 4 bushels/acre (Table 9). The greatest yields were produced when soybeans received both fertigation and foliar protection (Table 9). Similar to corn, there was a wide range in yield response to fertigation among soybean varieties. The range in yield response to the fertigation and foliar protection treatments can be observed when focusing in on a subset of the soybean varieties with a range of relative maturities within one company (Table 10). There was a general trend for the longer-season soybean varieties to have greater yields. In the shorter season varieties (S25-L9 and S28-D3), there was greater yield increase due to fertigation than foliar protection, approximately 13 versus 4 bu/ acre increase, respectively (Table 10). In contrast, the fuller-season varieties (S35-A5 and S37-Z8) had average yield increases of approximately 5 bu/acre with either fertigation or foliar additions, and these increases tended to be additive (Table 10). The variation in yield responses of different soybean varieties to fertigation or foliar protection highlights the importance of soybean variety selection. Summing up Using a subsurface drip irrigation system to precisely deliver fertilizer to the root zone successfully increased yields in both corn and soybeans in central IL in 2015, which was a season without need for irrigation. Applying fertigation throughout the growing season increased yields, on average, by 52 bu/acre for corn and 8 bu/acre for soybeans, with maximum yield increases up 30% to 40%, depending on variety or hybrid. Typically, a greater planting population is necessary for increasing yields, however, fertigation enabled corn to maximize yield, even at a population of 32,000 plants/acre. Soybean yield was increased both by fertigation and foliar protection. However, the magnitude of response was dependent upon genotype. These hybrid and variety differences in response to fertigation suggest a need for characterization of optimal genetics for enhanced nutrient use and additional yield improvement. 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. “Applying fertigation throughout the growing season increased yields.”