Abstract
A major constraint to agricultural production in acid soils of tropical regions is the low soil P availability, due to the high adsorption capacity, low P level in the source material and low efficiency of P uptake and use by most of the modern varieties grown commercially. This study was carried out to evaluate the biomass production and P use by forage grasses on two soils fertilized with two P sources of different solubility. Two experiments were carried out, one for each soil (Cambisol and Latosol), using pots filled with 4 dm³ soil in a completely randomized design and a 4 x 2 factorial scheme. The treatments consisted of a combination of four forage plants (Brachiaria decumbens, Brachiaria brizantha, Pennisetum glaucum and Sorghum bicolor) with two P sources (Triple Superphosphate - TSP and Arad Reactive Phosphate - ARP), with four replications. The forage grasses were harvested at pre-flowering, when dry matter weight and P concentrations were measured. Based on the P concentration and dry matter production, the total P accumulation was calculated. With these data, the following indices were calculated: the P uptake efficiency of roots, P use efficiency, use efficiency of available P, use efficiency of applied P and agronomic efficiency. The use of the source with higher solubility (TSP) resulted, generally, in higher total dry matter and total P accumulation in the forage grasses, in both soils. For the less reactive source (ARP), the means found in the forage grasses, for use efficiency and efficient use of available P, were always higher when grown in Latosol, indicating favorable conditions for the solubility of ARP. The total dry matter of Brachiaria brizantha was generally higher, with low P uptake, accumulation and translocation, which indicated good P use efficiency for both P sources and soils. The forage plants differed in the P use potential, due to the sources of the applied P and of the soils used. Less than 10 % of the applied P was immobilized in the forage dry matter. Highest values were observed for TSP, but this was not reflected in a higher use efficiency of P from this source.
Highlights
A major constraint to agricultural production in the acid soils of tropical and subtropical regions is the low soil P availability, since the soil adsorption capacity is high and nutrient contents of the source material, as well as the efficiency of P uptake and use of most modern varieties grown commercially are low (Novais & Smyth, 1999)
The total dry matter production (TDM) was higher when the grasses were fertilized with the source of higher P solubility (TSP), with the exception of Brachiaria decumbens and millet, grown on the Latosol (Figure 1a and b)
There was a similar trend in TDM production (Figure 1a,b), that is, in both soils, the Agronomic efficiency of P (AEP) values were higher when the grasses were fertilized with TSP, except for Brachiaria decumbens and millet on Latosol
Summary
A major constraint to agricultural production in the acid soils of tropical and subtropical regions is the low soil P availability, since the soil adsorption capacity is high and nutrient contents of the source material, as well as the efficiency of P uptake and use of most modern varieties grown commercially are low (Novais & Smyth, 1999). These conditions have required the application of high rates of phosphate fertilizers, and are a constant concern of the scientific community, intensifying the search for more efficient plants in P uptake and use, with a view to raise crop yields, reduce production costs and reduce environmental damage. According to Novais & Smyth (1999), the fertilizers with lower reactivity that make P available more slowly, minimize the fixation processes and may favor an improved nutrient use by crops
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