Masters Theses

Date of Award

8-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Michael Mullen

Committee Members

Paula Gale, Don Tyler

Abstract

In the past and to a lesser extent today, plant nutrient requirements were met by land applying livestock manure. Animal manure is the world's oldest fertilizer yet it is no longer used completely on agricultural lands despite its being produced in increasing quantities. Applications of manure can beneficially affect soil nutrient status. Manures accomplish this by serving as an energy source for soil microorganisms that release soil nutrients. For this reason manure is considered a slow release fertilizer. The slow release nature of manure nutrients allows them to accumulate in soil following a single application. The slow release nature of manure nutrients coupled with their accumulation in soil organic nutrient pools complicates fertilizer nutrient recommendations. In the past available P (AP) was based solely on a single, chemically extracted Pi pool. This practice fails to account for contributions to the AP pool from mineralization of labile organic P (Po) pools. Failure to account for contributions from Po coupled with continued manure P inputs has led to a build-up of soil test P levels which, in turn, has become an environmental rather than an agronomic concern. Non-point sources of P leaving the agricultural landscape are increasingly responsible for the eutrophication of surface waters and the associated growth of undesirable aquatic plants. To this end researchers advocate the inclusion of Po in soil P tests. Thien emd Myers (1992) introduced the use of soil microorganisms as a bioextractant for use in development of a bioavailable P (BAP) index. One of the objectives of this work was to evaluate this BAP method developed by Thien and Myers (1992) for use in soils receiving dairy cattle manure at two locations in Tennessee. Soils were collected from the Martin Agricultural Experiment Station (MAES) and the Dairy Experiment Station (DES) in Lewisburg. The MAES site had not received manure prior to the onset of this work, whereas the DES site had received periodic manure applications over the previous 35 years. Manure applications stopped in 1996 but sampling continued in 1997. The sites at these two locations provided insight into the effects of short and long-term manure management on soils susceptible to nutrient losses by surface runoff and leaching which contribute to pollution problems. Total nitrogen treatments included four rates of liquid dairy manure (126,252,378, and 504 kg manure N ha1), one NH4NO3 rate (218 kg N ha1), and a control (0 kg N ha1). The 378 kg manure N ha"' treatment was not included at DES due to the lack of space. The MAES sites were cropped to no-till silage com in the summer followed by an annual ryegrass-crimson clover winter cover and hay crop. Plots at DES were cropped to no-till silage com followed by a winter wheat cover. Available P was determined by Olsen's 0.5 MNaHCO3 extract (Kuo, 1996), Mehlich I extract (Kuo, 1996), and BAP (Thien and Myers, 1992). In 1991 Mehlich I and BAP extracted significantly greater concentrations of AP than Olsen did (α = 0.05). This resulted primarily from the Olsen extract containing Pi only. The AP concentrations extracted by Mehlich I and BAP were statistically the same in all but the 378M and 504M in the 0-7.5 cm depth and the AN in the 7.5-15 cm depth at MAES in 1996 (α = 0.05). Both Mehlich I and BAP extracted greater quantities of AP in the 0N and 126M than Olsen in the 0-7.5 cm depth. In plots getting the highest manure rates, Olsen and BAP extracted less A? than Mehlich I. At DBS Mehlich I extracted significantly greater quantities of AP in the 0N, AN, and 504M in the 0-7.5 cm depth and Mehlich I and BAP extracted similar concentrations of AP in the manured plots in the 7.5-15 cm depth (α = 0.05). In 1997, the AP concentrations in Mehlich I extracts were greater than those extracted by Olsens from all but the AN in the 7.5-15 cm depth and BAP except for the 504M in the 0-7.5 cm depth at MAES. At DBS in 1997, Mehlich I extractable AP was greatest for all treatments. Bach method had a strong positive correlation with silage com yields in 1996 at MABS with Mehlich I > Olsen > BAP (r = 0.77ttt, 0.74ttt, 0.68tt respectively). These results indicate that Mehlich I extractable AP concentrations best reflect the amount of AP in Tennessee soils. We failed to see the kinds of results obtained by Thien and Myers with the BAP method (Thien and Myers 1992) and recommend the use of AP in Mehlich 1 extracts determined on the ICAP for estimating fertilizer rates in Tennessee.

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