Determination of Phosphate leaching from top soil after applying natural Fertilizers and artificial Fertilizers

Andreas Kurmann et al

Abstract

P leaching from agricultural land to ground water poses a threat to water quality, but it may be possible to controldissolved nutrient leaching by choosing appropriate management practices. The objective of this study was to evaluate the effects of natural and artificial fertilizers on dissolved P leaching from topsoil. Intact soil cores from neighboring grass paddocks ( using artificial or natural Agrissential fertilizer for the last three years) were collected. Soils were leached with rainwater in the laboratory and P loads (mg/l) were calculated. Soils receiving artificial fertilizer had  30% (n5) more dissolved reactive P in the excess water, than soils receiving natural fertilizer. After the addition of a know amount of natural P, the tests were repeated. Now the dissolved reactive P in excess water from soil receiving artificial fertilizer increased to an average of 77% (n5)in comparison with soil receiving natural fertilizer. These results suggest that the leaching of dissolved P compounds is influenced more by the type of fertilizer applied than tillage or cropping practices.

Introduction

The transport of P from agricultural soils to ground water through leaching is of environmental concern and a potentialrisk to human health (Gaynor and Findlay, 1995; Owens et al., 2000; Zhao et al., 2001). Until recently, P leaching was seldom considered a significant pathway for transporting agricultural P to surface waters because it was believed that most soils had a considerable P adsorption capacity. However, Heckrath et al. (1995) reported significant export of P in agricultural drainage, with between 66 and 86% of the total P load in the form of dissolved reactive P. Phosphates can cause eutrophication in freshwater waterways and as little as 20 to 30 mg P L^–1 can stimulate phytoplankton production (Daniel et al., 1998). Consequently, a limit of 0.10 mg ortho-P L^–1 in the ground water at the level of the mean high water table was set in the Netherlands (Breeuwsma et al., 1995). An other good example is the biggest Lake in Central Europe

Lake Konstanz

Phosphate level in 1951                8 µg/l

Phosphate level in 1977                  86 µg/l  = 0.086 mg/l

Phosphate level in 2007                    8 µg/l

New regulations in 1980 which stopped the use of phosphate in washing detergent and limited the level of Farm runoffs

to < 0.05 mg/l P, as well as no use of phosphate leaching Fertilisers in the catchments area of lakes and waterways.

Agricultural practices such as tillage, cropping systems, and fertilizer applications influence soil nutrient concentrationsand drainage rates, leading us to believe that it may be possible to control dissolved reactive P leaching fromagricultural soils by choosing appropriate management practices.

Gaynor and Findlay (1995) reported that 3-yr average concentrations of dissolved reactive P in the tile drainage waters were 0.24 mg L^–1 for conventional tillage, and 0.54 mg L^–1 for zero tillage. Sharpley et al. (2001) suggested that no tillage reduces soil erosion; thus decreasing particulate P losses, but increases water infiltration, therefore increasing dissolved P losses. Conventional tillage destroys macropores (e.g., soil cracks, root channels, and earthworm burrows) (Hangen et al., 2002) and could reduce the dissolved P lost through leaching.

Dissolved P lost from cropping systems by leaching are probably influenced by the amount, timing and method offertilizer application, the residual amount of P in soils, as well as the rate of P mineralization from decomposing crop residues.

Another factor affecting nutrient leaching is the type of fertilizer applied. Differences in P leaching from artificial and natural fertilizer sources may be related to soil properties and the P fertilizer rate applied. The potential for dissolved reactive P loss through leaching can be predicted using soil test P andsoil P saturation values (McDowell and Sharpley, 2001a; Maguire and Sims, 2002; Sims et al., 2002).

The objectives of this study are comparing  artificial and natural fertilizer sources on, dissolved reactive P,  leached from the 0- to 400-mm layer of five different  soil types to determine whether dissolved P loads in leachates were related to them.

Material and Methods

Five field site were chosen in the Northland area of New Zealand. In each area a farm or orchard using Rok Solid or organic 100 has been compared against the neighboring farm or orchard using artificial fertilizers. The soil of field site 1 & 2 was a mixture of clay loam and sediment. The soil of field site 3 & 4 was slightly loamy sand. The soil of field site 5 & 6 was sandy loam. The soil of field site 7 & 8 was loam and the soil of field site 9 & 10 was very rich , nearly compost.

10 galvanized steel cores ( 60 mm x 400 mm ) have been used to collect the soil samples.

On each site two soil core samples have been taken. The first one from a farm  using natural fertilizers. The core was driven into the ground between 20 and 30 meter from the boundary fence. The second soil sample was taken from a farm using artificial fertilizer. Again a core was driven into the ground between 20 and 30 meters from the boundary fence. We made sure, that the sample have been taken on the same horizontal line and from the same soil type, to exclude soil type differences and excess water drainage.

In the Laboratory the soil samples of all ten test cores have been conditioned with distilled rain water, until at least 50 ml of excess water could be collected at the bottom of each tube.

The dissolved reactive P concentrations in leachates were determined. This would be the initial P reading in the excess water. For 4 weeks, each week 100 ml of rain water was added to each core and the excess water disregarded. In the fifths week, to each of the ten cores, 50 mg organic P was added in 100 ml of rain water ,the excess water collected and the dissolved reactive P concentrations in leachates were determined.

Using a very conservative approach and taking the initial P level in the excess water from each core of the P readings after the addition of organic P, there is clear indication, that the P leaching of excess water after applying natural Agrissential fertilizers is significant lower in comparison with artificial fertilizers.

Dependent on  the soil type, natural fertilizers have reduced the P leaching from top soil between 31.6 and 168.3 %. Previous studies have shown; it is critical which type of fertilizers are used. Inorganic slow release P, like in Rok Solid or organic P, like in Ocean 100 leaches less than artificial P.

Conclusion

By comparison, the loss of P through leaching from the top soil into the subsoil and waterways could be significant reduced after the continuous use of natural fertilizers versus artificial fertilizers.

Acknowledgments

Financial support for this project was provided by Agrissential Limited New Zealand. Thanks are extended to Grant Fallon for help with soil core collection .The helpful suggestions of anonymous reviewers were also appreciated.

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