Vol.4, No.12A, 39-49 (2013) Agricultural Sciences http://dx.doi.org/10.4236/as.2013.412A004 Phosphorus and potassium fertilization in no till southern Brazilian soils Jairo André Schlindwein 1* , Leandro Bortolon 2 , Elaine Cosma Fioreli-Pereira 1 , Elisandra Solange Oliveira Bortolon 2 , Clesio Gianello 3 1 Department of Soil, Federal University of Rondônia, Rolim de Moura, Brazil; * Corresponding Author: jairojas.estagio@yahoo.com.br 2 EMBRAPA—National Research Center of Fisheries, Aquaculture and Agricultural Systems, Palmas, Brazil 3 Department of Soil Science, Federal University of Rio Grande do Sul, Porto Alegre, Brazil Received 9 October 2013; revised 13 November 2013; accepted 24 November 2013 Copyright © 2013 Jairo André Schlindwein et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Phosphorus (P) and potassium (K) levels in southern Brazilian (Rio Grande do Sul, RS) soils are largely below the critical concentrations more than four decades after implementation of the officially recommended system. This study aims to evaluate the increase in P and K levels in 0 - 10 and 0 - 20 cm deep samples from no-till soils using the Mehlich-1 (M1) and Mehlich-3 (M3) extractants as well as resin methods and to es- timate the amount of P 2 O 5 and K 2 O fertilizers necessary to increase the P and K soil levels by 1 mg·kg −1 . The study was conducted in fields cultivated using a no-till system (direct planting) to grow soybeans, wheat, maize, pasture, and cover crops and fertilized with P 2 O 5 and K 2 O. Soil samples were collected from the 0 - 10 and 0 - 20 cm soil layers and analyzed by the M1, M3, and resin methods. The results demonstrated that the P and K levels increased in the 0 - 10 and 0 - 20 cm layers. However, the amount of these levels increased depending on the source of phosphate fertilization and on the P and K ex- traction methods used. The amount of P 2 O 5 fer- tilization needed to raise the P level by 1 mg·kg −1 was greater in the 0 - 20 cm layer than in the 0 - 10 cm layer, and the amount of K 2 O fertilization needed to raise the K level by 1 mg·kg −1 was higher in the 0 - 10 cm layer than in the 0 - 20 cm layer. Keywords: P 2 O 5 ; K 2 O; Sample Depth; Soil Analysis Methods 1. INTRODUCTION Soybean, wheat and maize are the most commonly grown crops in the oxidized soil with low fertility of Rio Grande do Sul (RS), Brazil; their cultivation occupies an area of approximately 5 million hectares, and this amount of cultivated land has not changed greatly over the years [1]. Agricultural expansion in RS has been mainly due to the utilization of amendments and fertiliz- ers during the 1950s and 1960s; however, the conven- tional soil cultivation system that has been completely replaced by no-till farming methods since the 1990s. The average yields for crops grown in RS are lower than the average yields in some other Brazilian regions and other countries; in 2009/10, the soybean, wheat, and maize yields were 2570, 2100, and 4860 kg·ha −1 , respec- tively [1]. These yields are partially due to low soil fertil- ity [2-5]. However, when the supply of nutrients and other production factors are sufficient during the crop growth cycle, these yields are higher, reaching up to 3000, 3000, and 10,000 kg·ha −1 for soybeans, wheat, and maize, respectively [6-8]. In the most recent soil fertility survey performed by [5], after more than four decades of agricultural expan- sion and the use of amendments and fertilizers in RS, approximately 80% and 40% of the soil analyses con- ducted between 1998 and 2000 showed P and K levels below the minimum required for satisfactory yields, re- spectively. Thus, 424,000 tons of potassium in the form of K 2 O and 299 tons of phosphate fertilizers in the form of P 2 O 5 were needed annually [5], representing large investments in the industrial, transport, and agriculture sectors. Fertilizer costs are approximately 20% of the total crop investment in RS for soybeans, wheat, and maize grown under a no-till system [9]. Therefore, fertil- izer levels must be reasonable and based on calibration field studies to determine the specific nutrient amounts needed for maximizing economic efficiency, which is achieved when the soil fertility is raised to near the criti- Copyright © 2013 SciRes. OPEN ACCESS