Short- and Long-Term Phosphorus Dynamics in a Fertilized Ultisol under Sugarcane
1993
Ball-Coelho, B. | Tiessen, H. | Stewart, J. W. B. | Salcedo, I. H.
In Brazilian sugarcane production systems, P fertilizer represents a substantial input cost, yet it is used with low efficiency. Furthermore, extractants currently used to estimate available P in highly weathered soils are not satisfactory. Understanding soil P transformations is a prerequisite to improving estimates of available P and fertilizer use efficiency. We used a sequential P fractionation procedure to examine short-term dynamics of P from fertilizer, residue returns, and soil, and long-term changes in forms and quantities of soil P as a result of fertilization. Mulch and burn systems of residue management were imposed as treatments in field-grown sugarcane (Saccharum officinarum L.) in northeast Brazil. Both treatments had similar inputs of P from residues (8.7 kg ha⁻¹) but, despite the higher “available” P content of the ashes, more of the added P was mobilized and taken up by the plant in the mulch system, probably due to the presence of roots within the decomposing litter and more intense root exploration of the topsoil as a result of an improved moisture regime. This improved moisture and P supply was reflected in a 45% higher ratoon yield in the mulch treatment. Fertilizer P applied in a furrow 20 cm deep with the plant crop was concentrated in the more labile fractions, and had a residual effect on the first ratoon of about 30%. Over the long term (10 yr) there was accumulation (about 144 kg ha⁻¹) of fertilizer P in the top 30 cm (in both labile and stable fractions). Nearly one-half of the increase was in the first 7.5 cm of soil, a reflection of limited mixing of broadcast applications and uptake from the 7.5- to 15-cm layer. This work was supported by the Canadian International Development Agency (Project 01842 S23239). Contribution no. R725 of the Saskatchewan Institute of Pedology.
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