the Symposium on Wheats for More Tropical Environments - cimmyt

243• Ammonium sulfate [(NH4)2S04] as anitrogenous fertilizerLow phosphorus levelsPhosphorus is highly and universallydeficient in <strong>the</strong> Cerrados area.Therefore. correction of this deficiencyis imperative for <strong>the</strong> production of cropsin <strong>the</strong>se soils. Crop responses tophosphorus fertilization. as shown inFigure 6. include quite high yields. but<strong>the</strong> amount of phosphorus necessary isalso high, with economic levels being in<strong>the</strong> range of 250 to 500 kg P205/ha.Much work has been carried out ondifferent management strategies for <strong>the</strong>use of phosphorus, such as broadcastversus banded applications and a largesingle application versus smallerrepeated applications. This work issummarized in Table 2.,-These results show that. in <strong>the</strong> longterm, yields are determined by <strong>the</strong> totalamount of P205 applied; differentmethods of application give similarresults. However, it was observed thatbroadcast applications outyieldedbanded applications for <strong>the</strong> first crop;<strong>the</strong> opposite was found after <strong>the</strong> thirdcrop. An initial broadcast applicationseems to give better root developmentand. <strong>the</strong>refore, better water extraction.Low levels of o<strong>the</strong>r nutrientsInsufficient zinc and potassium veryoften limit yields on <strong>the</strong>se soils and<strong>the</strong>ir deficiencies need to be corrected.Nitrogen and sulphur usually becomedeficient after several years of cropping.1Ca + Mg (Meq/lOOg)2 3 430-S45.£.c: ..... 600-Q.)(:)7590105120Figure 5. Effect of varying rates of phosphorus (kg/ha) as SSP on <strong>the</strong>distribution of calcium + magnesium in <strong>the</strong> soil profile of a dark redlatosol. BrazilSource: Ritchey et al. (10)