Agriculture, Ecosystems and Environment 190 (2014) 43–51 Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment j ourna l h om epage: www.elsevier.com/locate/agee Special Issue: Crop–Livestock System Impact of an integrated no-till crop–livestock system on phosphorus distribution, availability and stock S.E.V.G.A. Costa a,∗ , E.D. Souza b , I. Anghinoni a , P.C.F. Carvalho c , A.P. Martins a , T.R. Kunrath c , D. Cecagno a , F. Balerini a a Department of Soil Science, Federal University of Rio Grande do Sul, PO Box 15100, Zip Code 91540-000 Porto Alegre, RS, Brazil b Department of Soil Science, Federal University of Pernambuco. Recife, PE, Brazil c Department of Forage Plants and Agrometeorology, Federal University of Rio Grande do Sul , Porto Alegre , RS, Brazil a r t i c l e i n f o Article history: Received 19 February 2013 Received in revised form 27 November 2013 Accepted 2 December 2013 Available online 19 December 2013 Keywords: Biological and geochemical forms Phosphorus fractions Phosphorus budget Integrated systems a b s t r a c t Biophysical and socio-economic improvements of farming systems have been obtained with integrated crop–livestock systems (ICLS). Grazing in ICLS under no-tillage conditions may alter soil phosphorus (P) dynamics, because of changes in P budgets and distribution of P forms. The need to understand impacts on P dynamics is important because they can modify soil quality and, consequently, have implications for agriculture sustainability. The objective of this work was to compare the geochemical and biological forms of P (P-geo and P-bio) under long-term grazing, as well as to assess the mobility and lability of these nutrient forms in the soil profile. The experiment was established in 2001 in an Oxisol and consisted of soybean (Glycine max L.) rotated to a winter cover crop of black oat (Avena strigosa Schreb.) and Italian ryegrass (Lolium multiflorum Lam.) under no-tillage management. Treatments were two grazing heights (target of 20 and 40 cm) with young cattle and a non-grazed (NG) treatment. The experimental design was set up in completely randomized blocks with three replicates. Soil was sampled at the beginning of the experiment (May 2001) and again after six years (May of 2007) to study P fractionation at depths of 0 to 2.5, 2.5 to 5.0, 5.0 to 7.5, 7.5 to 10, 10 to 15 and 15 to 20 cm. After six years of ICLS, total P increased in the top 20 cm soil layer in both the grazed and non-grazed treatments. The P-geo and P-bio concentrations also increased in all treatments in the 0 to 2.5-cm layer. Despite the greater P accumulation in the non- grazed no-till treatment, grazing maintained the P lability (labile + moderately labile) at the same level as in the long-term no-till treatment. The ICLS also promoted increases in labile P stocks, both in organic and inorganic forms. In spite of the higher P-geo stocks in the non-grazed treatment, P cycling was enhanced by grazing, such that soybean yields were similar in all treatments. Furthermore, the grazing treatment led to higher P budgets (surpluses) and more efficient P use, as represented by meat production in addition to the soybean production. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Designing food production systems that supply the demand of a growing world population and maintain biogeochemical cycles to support the earth’ ecosystems is perhaps the biggest challenge faced by humanity. Furthermore, the world’ poor people are under great hunger, and an increase in food prices is a threat to global peace and stability (Lal, 2009). Such conditions have made tech- nical efficiency a priority in farming systems. Specialization and diversification are essential for researchers seeking to reform food production systems. Positive results have been observed in the biophysical and socio–economical dynamics of farming systems following the adoption of ICLS (Keulen and Schiere, 2004). Although ∗ Corresponding author. Tel.: +55 51 81829776; fax: +55 51 34075082. E-mail address: sergioelycosta2011@hotmail.com (S.E.V.G.A. Costa). grazing is highly contested in cash crop areas, numerous long- term trials have shown that when they are managed well, animals enhance the equilibrium of the soil–plant–atmosphere continuum (Sandini et al., 2011). Grazing impacts on nutrient cycling are most likely the main effect of ICLS on the soil–plant–atmosphere continuum when com- pared to non-grazing systems, even under no-tillage (NT) practices. According to Cavalcante (2001), grazing promotes nutrient flux modifications, animals are considered to be catalysts, and soil is the central compartment in which nutrient cycling processes occur (Carvalho et al., 2010). Understanding and evaluating these modi- fications becomes a priority when dealing with nutrients such as P, which has limited availability in highly weathered soils (Lawrence and Schlesinger, 2001). Anghinoni and Assmann (2011) considered residues (animal + plant) to be a source of P (inorganic + organic), and showed that slow P release can restrict the possibility of sorp- tion reactions with Fe and Al hydroxides, enabling a higher P use 0167-8809/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.agee.2013.12.001