Abstract
The objectives of this study were to assess the concentrations of available phosphorus (P) extracted using the Mehlich-1 (M1), ion exchange resin (IER) and modified Morgan (MM) methods after 36 months of experimentation with the application of phosphates in a crop-livestock integration system (CLIS). Moreover, this study aimed to assess which extraction method provides the best correlation of P concentrations with the maize crop attributes. The treatments consisted of applying annual doses of P2O5 on the soil surface of the total area during the sowing of winter forage crops in the form of triple superphosphate (TSP), rock phosphate (RP) or magnesium thermophosphate (MTP). After 36 months of experimentation, soil samples were collected from the 0-5, 5-10, 10-15 and 15-20 cm layers to assess the concentrations of available P. The dry matter yield (DMY), the grain yield (GY), the accumulation of phosphorus in the dry matter (P-DM) and the export of phosphorus (P-Ex) were quantified in maize. The IER method extracted greater amounts of available P, followed by the M1 and MM extractions. The treatments that included the application of TSP and either the M1 or IER extractions had similar efficacies when correlated with the DMY, GY, P-DM and P-Ex attributes of maize. The P extracted by the IER was most correlated with P-DM and P-Ex for the water-insoluble P sources (RP and MTP). The MM solution was ineffective at predicting the availability of P for maize grown in a soil with that had received varying doses and sources of P applications in a CLIS.
Highlights
Crop-livestock integration systems (CLIS) combined with no-tillage (NT) have been increasingly used in farms of southern Brazil (BALBINOT JUNIOR et al, 2009)
The experimental design used for the study consisted of randomized blocks in an incomplete factorial scheme (3x3+1) with four replicates and ten treatments, namely: Treatment 1 (T1) without P application; T2, T3 and T4 consisting of the application of 60, 120 and 180 kg ha-1 of total P2O5, respectively, in the form of triple superphosphate (TSP) with 460, 380 and 130 g kg-1 of total P2O5, water-soluble P O and calcium oxide (CaO), respectively; T5, T6 and T7 consisting of the application of 60, 120 and 180 kg ha-1 of total P2O5, respectively, in the form of rock phosphate (RP) (Arad) with 330, 100 and 370 g kg-1 of total P O, 20 g L-1
The similar results of the present study indicate that the modified Morgan solution might not be effective in assessing P bioavailability for maize in clayey soils cultivated under crop-livestock integration system (CLIS)
Summary
Crop-livestock integration systems (CLIS) combined with no-tillage (NT) have been increasingly used in farms of southern Brazil (BALBINOT JUNIOR et al, 2009). The management of soil fertility is a key practice to achieve high yields in production systems because Brazilian soils are highly weathered and low in phosphorus (P) (NOVAIS; SMYTH, 1999). In that context, supplying P has been an essential practice in Brazil, and the source of the phosphate used has resulted in different crop responses (RESENDE et al, 2006; SANTOS; GATIBONI; KAMINSKI, 2008). The methods of P application have been diverse, and the most commonly used in grain production are (i) row placement, (ii) soil surface and (iii) band placement (SANTOS; GATIBONI; KAMINSKI, 2008). Anticipated broadcast applications of phosphate fertilizers in NT systems have been shown to provide high grain yields of soybean and maize (BERTOLINI et al, 2008; BOHAC; CÂMARA; SEGATELLI, 2007), making it an interesting alternative for CLIS
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