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Fluid Journal : Fluid Journal 2008-2009
WINTER 2008 Fluid Journal 21 or three rates of N, often including application immediately before sowing and four to twelve weeks after sowing. In 107 of the 132 comparisons of UAN and granular urea at the same rate of N and time of application, there was no difference between fluid N and granular urea for grain yield. Despite differences in N form, fluid N applied through a boom spray was as effective as broadcast- applied urea for the vast majority of wheat and canola crops in WA. In a paddock scale trial, topdressing granular N resulted in uneven application compared with the boom spray application of fluid N. Uneven distribution could reduce crop performance and thus profitability. In ten studies over three years, fluid N banded near the seed was compared with fluid N applied through the boom and granular urea banded and/or topdressed. In seven out of the ten studies, there was no significant difference in yield between either product when topdressed or banded, although early nutrient uptake and growth were improved with banding. There has been a growing interest among WA farmers in the application of fluid N through liquid injection systems on seeders. The results from 22 trials conducted suggested that compared with fluid N boom sprayed, banded fluid N improved N-use efficiency, which could lead to a decrease in N application rate while still maintaining the same yield. Effect on grain protein. There is very limited published information available to review on this subject in WA. Trials conducted at Buntine and Kojonup showed that in high- yielding situations, late application of fluid N could be used to boost wheat protein content and profits but suggested that more work would be needed to avoid the problem of leaf scorch or burn when using such late fluid N applications. Post-emergence applications of fluid N can cause leaf scorch or burn so that the reduction of the leaf area of the damaged crop might slow its growth and limit final yield. Leaf scorch has been considered an important problem in limiting use of fluid N. Late applications of granular urea or UAN at flowering to boost wheat grain protein content could be risky in WA climatic conditions where flowering often coincides with periods of water deficit that could affect the capacity of crops to use fluid N. However, in dry conditions, fluid N could be absorbed through the plant's leaves and should provide a more reliable protein boost than topdressed granular urea since fluid N can only be used to lift protein when significant amounts of rain wash N into the rooting zone. The extent of dryness of soil or the incidence of rainfall during late applications of N will most likely determine how effectively fluid N could improve protein compared with granular urea. A significant aspect of fluid N use is the potential for late N applications to adjust N supply in line with yield expectations and improve protein content of the grain. Fluid N will be best suited as a tactical N management tool for boosting protein in crops that are likely to exceed target yields and where dry surface soil conditions limit the capacity of roots using N applied as granular. Fluid P Effect on grain yield. One study over the period 2000 to 2005, for example, reported that fluid P applications resulted in 8 to 31 percent increases when compared to granular P (Table 1). All response sites had high P-fixing soils. Increased efficiency. Depending on soil pH, P in soil solution generally occurs as the anions, H2PO4- or HPO42- . These anions readily react with soil cations, such as Ca, Mg, Fe and Al, to form various phosphate compounds of low water solubility. Phosphorous reactions vary with soil pH. Highly weathered low pH soils generally contain large amounts of soluble Fe and Al that react with soluble P compounds in the soil to form Fe- and Al-phosphates, whose solubility Table 1. Summary of sites where fluid P produced significantly greater yield than equivalent rates of granular P in WA. Site Year Soil type Soil pH Yield increase (CaCl) (%) Dandaragan 2000 Sandy loam 5.5 9 Salmon Gums 2001 Clay loam 8.0 11 Mukinbudin 2001 Loam 7.5 8 South Cross 2003 Sandy loam 4.4 31 West Dale 2003 Gravelly loam 5.4 29 Newdegate 2005 Loamy sand 5.2 8
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