Li. Prochnow et al., INFLUENCE OF CATIONIC IMPURITIES IN ACIDULATED PHOSPHATES ON THE AVAILABILITY OF PHOSPHORUS TO 2 CORN CROPS, Communications in soil science and plant analysis, 28(15-16), 1997, pp. 1375-1391
Based on the problems that arises from the presence of cationic impuri
ties in rock phosphates for fertilizer production, a greenhouse experi
ment consisting of two consecutive corn crops was conducted in order t
o evaluate the plant availability of phosphorus (P) in the fraction so
luble only in neutral ammonium citrate (NAC) and also in the NAC+H2O f
raction of acidulated phosphate fertilizers produced from Brazilian ra
w materials with different amounts of cationic impurities. The experim
ent was conducted with samples of a Red-Yellow Latosol (Typic Hapludox
) in a completely randomized design with four replications. Four acidu
lated phosphates obtained by sulfuric acid (H2SO4) solubilization of d
ifferent Brazilian raw materials were studied. Monocalcium phosphate [
Ca(H2PO4)(2) . H2O] (MCP) was included as a standard source of P as we
ll as samples which were previously leached to remove the water-solubl
e P, and therefore, contained essentially the NAC-soluble fraction. Th
e fertilizers were thoroughly mixed with the whole soil in the pots (m
ixed application), or with only 1% of its volume (localized applicatio
n), at the rates of 50 and 100 mg P kg(-1), based on the calculated co
ntent of P soluble in NAC+H2O. Corn (Zea mays L.) was the test crop gr
own in two sequences of 35 days. After each 35-day period, dry matter
yield and P accumulated in the plant tops were determined. Results wer
e evaluated by analysis of variance considering the factors, (i) acidu
lated phosphates, (ii) rate of P application, (iii) leaching, and(iv)
methods of application. In a second analysis, the leached phosphates w
ere considered as additional levels of the phosphate factor as well as
for MCP. The Tukey test at the 0.05 significance level was utilized f
or mean separation. Results from this study clearly demonstrated that
increasing the amounts of cationic impurities in the raw materials dec
reased the concentration of water-soluble P and NAC+H2O-soluble P as w
ell as water-soluble P and NAC+H2O-soluble P ratio of the fertilizer o
btained. From the results in the first corn cropping, the P in the NAC
fraction for the studied Brazilian phosphate was not as available to
plants as was the P in the NAC+H2O fraction or in the pure MCP. The NA
C+H2O method was not an adequate index for evaluating the P availabili
ty of the studied sources. No interaction between P sources, leaching,
and method of application was found in the second corn cropping.