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Effects of Root Temperatures and Nitrogen Carriers on Nutrient Uptake, Growth, and Composition of Pineapple Plants, Ananas comosus (L.) Merr.
|Title:||Effects of Root Temperatures and Nitrogen Carriers on Nutrient Uptake, Growth, and Composition of Pineapple Plants, Ananas comosus (L.) Merr.|
|Authors:||Ravoof, Azeez Abdul|
|Abstract:||The effects of four root temperatures (15, 20, 25 and 30 C) and three N-carriers /_ ammonium nitrate (AN), ammonium sulfate (AS) , and sodium nitrate (SN)_/ on the uptake of nutrients, and the growth and composition of pineapple plants of the Smooth Cayenne variety, grown in complete nutrient solutions for 40 days were investigated.|
The results on cumulative water and nutrient absorption indicate severe root injury at 15 C, and mild injury at 20 C root temperatures. Increases in root temperatures significantly increased water and nutrients absorbed. The optimum for N and K absorption was close to 25 C, but the optimum for water absorption probably is higher than 30 C. The optimum root temperature for the uptake of P, Ca, and Mg was different for different N-carriers.
The uptake of N and P was highest, and K, Ca, Mg and water was lowest in the AS culture; the reverse was true in the SN culture. Values for the absorptions of these ions in the A N culture were between those values for the AS and SN cultures. Calcium absorption was completely inhibited and K absorption severely inhibited with the use of AS. It appears that the presence of an easily absorbable anion such as NO^, eliminates the inhibitory effect of NH^ on K absorption (as happens with the use of AN) and K on Ca absorption (as happens with the use of SN). The ratio of NO2 to K absorption was almost 1:1, and that of NO^ to Ca 6:1. The absorption of NO3 from AN culture was higher (60%) than that of NH4 (40%), indicating possibly that pineapple plants "prefer" NO3 to NH4.
The absorption ratios of K:N, K:P and N:P and the total amount of alkali cations (K + Ca + Mg) absorbed were highest with the use of SN, lowest with AS, with the values for AN between those for SN and AS. The total amounts of anions and alkali cations absorbed were nearly equal, regardless of the root temperatures and N-carriers.
Plant growth increased with increases in root temperatures; the use of AN and SN produced larger plants than AS regardless of root temperatures. At 15 C, there was a loss of plant weight with all three N-carriers probably due to leaf desiccation. Root weights in the SN cultures increased continuously up to 30 C. In the AN cultures root weights increased only up to 25 C, whereas, with the use of AS, root weights increased only up to 20 C with an actual decrease between 25 and 30 C; however, the capacity of roots to absorb nutrients was unaffected in the latter case. . Stem weights were slightly greater with the use of AS than with AN and SN. The weights of leaves which constitute more than 7 5 % of the total plant weight, increased continuously with increases in root temperatures; increases were higher with the use of AN and SN than with AS. The efficiency of nutrient utilization for growth was high with the use of SN and AN, but low with AS. Especially, N utilization efficiency with the use of AS was poor, probably as a result of "luxury consumption" of N or a lack of K for proper N metabolism or both.
A 20 C root temperature appeared to be high enough for absorption and assimilation of N in roots, but was not high enough for the translocation of these metabolites from roots.
The soluble, protein and total-N fractions in roots, stems and leaves, as well as the asparagine and total amide content of leaves were highest with AS, lowest with SN, and with values for A N lying between those for AS and SN. These results present additional evidence for the inefficient utilization of N with the use of AS, probably due to insufficient available K.
In the leaf hydrolysates an unknown amino acid-type compound, which absorbed at 440 mu wave length (similar to proline and its derivatives) was observed. This unknown showed a significant negative correlation with root temperatures and plant growth.
In conclusion, it appears that for better and more balanced nutrient absorption, a better utilization of these nutrients for growth, a nitrate or a mixed nitrate and ammonium source is desirable. Also, for better K and Ca absorption, especially where poor nitrification is suspected, the addition of an easily absorbable anion like NO3 is essential.
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Ph.D. - Agronomy and Soil Science|
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