UBC Theses and Dissertations
Uptake, leaching, and storage of micronutrient metals in response to heavy applications of poultry manure Safo, Ebenezer Yeboah
The partitioning among plant uptake, leaching from and storage in soil of micronutrient metals following heavy applications of poultry manure was studied in three greenhouse experiments. Following these experiments, the study examined the effect of manure application on content and composition of soil organic matter and also the distribution of metals in the organic fractions. Poultry manure was surface-applied to Grigg and Monroe silt loam soil columns at rates of 0, 20 and 40 t/ha in each of the first two experiments, whereas the third tested the residual effect of the manure applications. Treatments were replicated four times and completely randomized. The soil columns were planted to corn (Zea mays L.) and leached daily with demineralized water at an average rate of 1.0 cm/day for 30-40 days. Following leaching and harvest of the corn, the soil columns were sampled in two sections for chemical analysis. Metals in the soils, leachates and corn tissue were determined by atomic absorption spectrophotometry. Manure application significantly (P < 0.01) influenced corn yield in Experiments I and II. The 20 t/ha rate increased yield more than the 40 t/ha treatment. Yield increases over the check treatment in Experiment I were about 400% and 300% from the 20 and 40 t/ha treatments respectively. In Experiment II, yield response was significantly curvilinear (P < 0.01), with the 20t rate giving the highest yield. The possibility of NH₃ toxicity and excess soluble salt injury resulting from the 40 t/ha rate was suggested. In Experiment III yield increases over the check treatment were about 300% and 500% from the 20 and 40 t/ha previous rates respectively. The study found no evidence for significant uptake or leaching of the toxic heavy metals (Cd, Cr, or Pb), such as is usually encountered with sewage sludge application. In Experiments I and II, total uptake of Mn, Fe, Zn, and Cu increased with the application of 20 t/ha and then decreased with the 40 t rate. In Experiment III, previous manure applications led to increases in uptake of these metals. The concentration of these metals in corn tissue decreased with the application of 20 t/ha and then increased with the 40 t rate in Experiment I. However, In both Experiments II and III the tissue metal concentration decreased with manure application. These effects were attributed largely to changes in yield. However, in no case did changes in concentration of metals exceed suggested tolerance limits. These results suggested that relatively high rates of poultry manure may be applied to the soil without appreciable danger of developing conditions of micronutrient metal toxicities. High manure rates led to increased leaching losses of K and Na. However, leaching losses of Mn, Fe, Zn, and Cu decreased with the application of 20 t/ha and then increased with the 40 t rate. Assuming independent contributions of metals from various potential sources, ratios of uptake and leaching losses to the input sources were examined. Both uptake and leaching losses of metals were small in magnitude in comparison with initial soil total levels and manure input. Despite the varied patterns of uptake and leaching losses of metals in response to the manure application, their storage in soil increased with rates of application. There was no consistent pattern in the distribution of metals in the top and lower halves of the soil columns after Experiments I and II. Examination of the distribution of organic fractions and associated metals following the greenhouse experiments indicated that soil organic matter content increased with manure application. The humic acid fraction made up 69 to 75% and the fulvic fraction 25 to 31% of the soil extractable organic matter. Despite such a high proportion of organic matter in the humic fraction, the data indicate that a greater proportion of metals in the organic fraction was associated with the fulvic fraction.
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