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Fluid Journal : Winter 2012
11 The Fluid Journal Winter 2012 Drs. G. Hettiarachchi, D. Mengel and Mr. Khatiwada P management in reduced-till has been a concern for farmers. Understanding Inﬂuence Of P Placement Under Field Conditions The Fluid Journal • Ofﬁcial Journal of the Fluid Fertilizer Foundation • Winter 2012 • Vol. 20, No. 1, Issue # 75 Phosphorus management in reduced- till systems has been a great concern for farmers. It has been found that P application, mostly in granular forms, leads to an accumulation of available Ponthesurface0to5cmofsoillayer and a depletion of available P deeper in the profile. Deep placement of nutrients below the first 5 to 10 cm of the soil should be superior to other placements when nutrient stratification, coupled with topsoil moisture deficit, reduces nutrient uptake from shallow soil layers. Inconsistent results have been obtained from the research conducted to study the effects of tillage and deep placement of P fertilizers on grain yields of crops grown in Kansas. Knowledge of the dominant solid P species present in the soil following application of P fertilizers, and linking that to potential P availability, would help understand how to manage P in efficiently reduced-till systems. The objective of this research was to understand the influence of placement (broadcast vs. deep-banded P), fertilizer source (granular vs. liquid P), and time on reaction products of P under field conditions. Materials/methods Site. A field-based study was performed at the Agronomy North Farm located in Manhattan, Kansas. This site has a history of more than five years of reduced-till studies. Sources. Two P fertilizer sources were granular mono-ammonium phosphate (granular MAP) and technical grade MAP (liquid MAP). Application. Phosphorus was applied at 75 kg/ha and N, as urea, was applied at 200 kg/ha. Urea was broadcast (control) and deep banded (control). Granular Summary: Despite various advantages of reduced-till systems, it has been found that surface application of phosphorus (P) leads to an accumulation of P in the surface 0 to 5 cm of soil layer and a depletion of available P deeper in the profile. We measured changes in soil pH, resin extractable P, and speciation of P at five-week and six-month intervals after P application to a soil system that was under long-term reduced-till. Resin extractable P was lower for broadcast treatments as compared to deep-band treatments for both the time periods. Resin extractable P was greater for liquid P-treated soils when compared to the granular P-treated soils. Speciation results showed that granular P fertilizers tended to form iron (Fe) phosphate-like products whereas liquid forms were found to remain in adsorbed P-like forms in soil five weeks after application. Over the six-month period, reaction products of broadcast/ granular and broadcast/liquid and deep-banded/ granular fertilizers transformed to Calcium (Ca)-phosphate or mixtures of Ca-, Fe-, aluminum (Al)- and adsorbed phosphate-like forms while deep-banded liquid P continued to remain mainly as adsorbed P-like forms.
Early Spring 2012