Variation in soybean response to early season foliar fertilization among and within fields

Foliar fertilization of crops can complement soil fertilization. Recent research showed that soybean [Glycine max (L.) Merr.] yield response to early season N-P-K foliar fertilization was inconsistent and difficult to predict. This study's objectives were to further evaluate soybean response to early season N-P-K fluid fertilizers with or without S or micronutrients and to assess the within-field response variation. The mixtures 3-8-15 (N-P-K), 3-8-15-1 (N-P-K-S), 10-4-8, 10-4-8-1, and 10-4-8-1 plus B, Fe, and Zn were evaluated in 18 conventional small-plot trials. The within-field variation in response to a 3-8-15 fertilizer mixed with glyphosate [N-(phosphonomethyl) glycine] herbicide was evaluated in eight strip trials harvested with combines equipped with yield monitors and differential global positioning systems receivers. A fertilizer rate of 28 L ha(-1) was sprayed once at the V5 growth stage. There was a yield response to the 3-8-15 and 10-4-8-1 fertilizers in one small-plot trial (260 kg ha(-1)) and to 3-8-15 fertilizer in another trial (360 kg ha(-1)). There was a small response to the 3-8-15 fertilizer across the 18 trials (93 kg ha(-1)). Soybean responded to 3-4-15 fertilizer only in one strip trial where the yield response was higher in acidic soil areas. No response variation was detected across contrasting soil test values or soil types within other trials. Soybean response to foliar fertilization across all production condition; will seldom offset fertilization costs. The probability of economic yield response could be increased if the fertilizer is mixed with a postemergence herbicide because application costs are reduced.