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Fluid Journal : Early Spring 2011
10 The Fluid Journal Early Spring 2011 Figure 1. Accumulated precipitation and evapotranspiration from September 1, 2008 to March 31, 2009 at INTA Exp. Stations of Parana (Crespo), and Pergamino. Figure 2. Treatment means pooling locations for grain and total dry matter yields. Figure 3. Treatment means pooling locations for protein content in soybean. Figure 4. Treatment means pooling locations for grain N uptake in soybean. spraying. By using slow/controlled release fertilizer, which may delay between 30 to 60 days its rendering of mineral N to crops (coupled with that early moment), the timing of N availability may offer a better synchronization with N demand without jeopardizing N fixation. Also, urea with a urease inhibitor like n-BTPT would prevent N losses by volatilization as NH3 but also at the same time avoid adding readily to available N as in the case of UAN. Having fertilizer-N available at late stages of soybean growth when fixed N would not be enough to support high yields on soybeans would boost grain yields without affecting symbiotically fixed N. The objective of this work was to evaluate the effect of increasing late N availability by improving placement/product combinations of fluid N sources on soybean grain yields and N uptake. Factoring weather In the 2008-09 season the whole region was affected by one of our worst droughts ever seen. Yields and treatment performance were hampered. Figure 1 shows the accumulated precipitation and evapotranspiration (ETP) from September 1, 2008 to March 31, 2009 during the growing season of the soybean crops. Notwithstanding, the soybean crop yielded some grain at all sites and showed a reasonable nodulation. It is assumed that N fixations performed according to the weather restrictions. However, there were significant differences in yield among the sites due to the weather pattern. While the Pergamino site showed Acevedo as one the lowest ever yields (1,244 kg/ha), the yields at the other locations showed a parallel with the rainfall received during the growing cycle. Only slightly more yield than the Acevedo site was obtained at Ocampo (2,058 kg/ha) while the northern locations were in the range of 2.2 mt/ ha (Mercedes and Crespo sites, respectively: 2,238 and 2,209 kg/ha). These yield locations resulted in a different response to treatments, with a significant statistical interaction (pr>F:0.09).