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CRAVO, M. D. S.

SMYTH, T. J.

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Micronutrient Fertilization on a TypicAcrorthox at Manaus, BrazilManoel S. Cravo, EMBRAPAThomas Jot Smyth, N.C. State UniversityAnnual crops have not provided significant yieldresponses to micronutrient applications during the in-itial years of cultivation on a Typic Acrorthox atManaus, Brazi\. A field study with micronutrient fer-tilization was iniriated in 1982 on previously cultivatedland in order to gain further information on themicronutrient status of this soi\. The experimental sitehad been cropped to a com-cowpea rotation duringthe five preceding years with N, P, and K as the solefertilizer inputs.T reatments, as described in T able 1, were establishedin a randomized complete block design with fourreplications. Two rates of each micronutrient testedwere established as separate treatments. The Complete1 treatment contained intermediate levels of eachmicronutriem in order to compare with the other levelsapplied. Micronutrients were applied only at plantingof the initial com crop. Ali other nutrients and limewere supplied by uniform applications to alI plots. Comand cowpeas were grown annually in rotation.CLAYEY OXISOLS-Yield Response to MicronutrientsYield differences among treatments were not signifi-cant for the six crops harvested. Cowpea yields ontreatrnents with micronutrients were similar to thetreatment without micronutrient fertilization (Table2). Yield trends for com in 1984 and 1985 suggesteda response to B and Zn. Foliar levels of B for comin 1983 approached the lower limit of the recommend-Table 1. Micronutrient fertilizer rates applied to the initial corncrop in the micronutrient study.Treatment B Cu Mn Znkg/haCjeck O O O O80 O 1 5 581 1 1 5 5CuO 0.5 O 5 5Cu2 0.5 2 5 5MnO 0.5 1 O 5MnO 0.5 1 10 5ZnO 0.5 1 5 OZn10 0.5 1 5 10Complete 1 0.5 1 5 5Complete 2 1 2 10 10Table 2. Relative yields of corn and cowpeas during six consecutive crops after micronutrient treatmentswere established.Corn CowpeasTreatment 1983 1984 1985 1983 1984 1985relative yield, %.Check 100 100 100 100 100 10080 96 102 101 102 100 9981 94 138 105 105 108 106 ICuO 79 111 104 91 102 89Cu2 98 126 ~5 109 108 94MnO 86 127 98 97 100 88Mn10 100 127 91 90 97 78ZnO 109 111 93 93 106 94Zn10 97 140 131 96 105 95Complete 1 87 146 112 100 103 99Complete 2 109 114 100 102 115 89CV(%) 18 22 19 11 11 16* Yields for the check treatment in t/ha were as follows: Corn, 1983: 2.7; corn, 1984:' 2.0; corn, 1985: 2.8; cowpeas,1983: 1.5; cowpeas, 1984: 1.4; cowpeas, 1985: 1.1.109CLAYEY OXISOLSed sufficiency range (Table 3). A!though Zn fertiliza-tion rates have provided consistent increases in Mehlich1 extractable soil Zn, no such differences have beenobserved in foliar Zn levels for com (Table 4). Foliarmicronutrient analyses have been impeded bylaboratory modifications and instrument problems.Mehlich 1 extractable Cu and Mn have declined dur-ing the three years of cultivation on treatments withand without the application of these elements (Table4). The absence of a yield response to Mn, despirethe low soil-test levels, may be related to themaintenance of soil pH within a range of 5.4-5.0.Other studies performed on-site have provided evidenceof Mn deficiency when soil pH was greater than 5.5.Conclusions1) Results thus far on this study have indicatedmarginal yield responses with com to B and Zn. TheseTable 3. Foliar B levels for the 1983 crops of corn andc wpeas as a function of B applied prior to plantingc rn.Leaf BTreatment Corn Cowpeasppm80 8 25Complete 1 5 3181 6 32elements have been included in blanket fertilizationsfor com in other on-site experiments wheremicronutrient deficiencies were to be avoided.2) Yield trends with cowpeas have suggested thatnative soillevels of rnicronutrients were sufficient forthis crop.Table 4. Leaf and soi! Zn levels and soi! Cu and Mn levels in three corn crops as a function of micronutrient rates.Mehlich 1 Extractable Foliar Analyses1984 1985Treatment 1983 1984 1985 1983Zn, ppmZnO 1.0 .8 .6 21Zn10 2.0 2.5 1.8 28LSD .05 .6 .8 .4 msCu, ppmCuO 1.8 1.8 0.3Cu2 2.8 1.8 0.6LSD .05 ns ns 0.1Mn, ppmMnO 5 2 2Mn10 7 2 4LSD .05 3 ns49 1452 10ns nsI110

Micronutrient fertilization on a typic acrorthox at Manaus, Brazil.

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Micronutrient fertilization on a typic acrorthox at Manaus, Brazil.

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