Error caused by carbon dioxide in determination of ammonium by direct steam distillation of tropical wetland rice soils

Abstract A study was made with eight Philippine wetland rice soils to quantify the possible error caused by the CO2 evolved during direct distillation of soil suspensions in aerobic and anaerobic conditions with MgO. The error caused by CO2 was eliminated by absorbing the ammonia distilled in H2SO4, which was gently boiled to derive off the CO2 absorbed. The possible error caused by CO2 was not eliminated when boric acid was used for absorbing ammonia. The difference in NH4 + values determined by using sulfuric acid and boric acid methods gave an estimate of the error caused by CO2. It was found that CO2 evolved caused negative error in the NH4 + values obtained using the direct distillation of soil suspensions with MgO in presence of KCl. The magnitude of error was higher and significant with anaerobic soil samples but this error was negligible with aerobic soils

Effect of carbofuran on transformation of urea nitrogen in soil

THE effect of Carbofuran at 10 and 50 ppm of soil on transformation of urea nitrogen in a sandy loam (PH 7-7) was studied in laboratory. The insecticide had no effect on urea hydrolysis but moderately inhibited both conversion of NH4+ to N02- and N02- to N03-, the effect being pronounced at the higher rate but lasted upto 2 weeks only. The results 0'£ the study along with other evidences suggest that under normal field application rates, carbofuran may have little effect on the hydrolysis as well as nitrification of urea nitrogen in soils with pH in the alkaline rang

Soil and Plant Testing for Iron: An Appraisal

Iron (Fe) deficiency chlorosis in crops is common in high-pH calcareous soils. Soil and plant testing is routinely used for diagnosing iron (Fe) deficiency chlorosis in crops, with mixed results. This article presents an overview of the factors that influence soil and plant tissue testing results. It is clear that soil tests for Fe are dominantly influenced by soil pH, bicarbonate, and moisture regime rather soil test result per se. This is because the solubility of Fe is more regulated by soil pH and moisture regime. Plant tissue testing for Fe can complement the results of soil testing for Fe. But at times, especially in calcareous soils, total Fe in plant tissue is not related to Fe deficiency, but metabolically active Fe is better at diagnosing the occurrence of the disorder. A combined use of soil and plant tissue testing seems more helpful in diagnosing Fe deficiency chlorosis disorder in crops

The role of tolerant genotypes and plant nutrients in reducing acid-soil infertility in upland rice ecosystem: an appraisal

Acid-soil-related infertility is a major constraint in the humid tropical regions. Soil infertility problems result from low pH, aluminum toxicity, phosphorus deficiency, low silicon and low base saturation, and the interactions between various deficiencies and toxicities. Phosphorus (P) deficiency is identified as a major nutrient deficiency in acid upland soils; and not only are the soils are low in P but also the applied soluble P is rendered unavailable due to reactions with iron and aluminum oxides. Upland rice cultivars differ in tolerance for and adaptation to acid soil conditions. In this paper, recent research on the role of tolerant genotypes adapted to acid soil conditions and plant nutrients, especially P, in reducing acid soil infertility in upland rice is reviewed. Synergy between genetic tolerance and P nutrition seems critical for sustainable productivity enhancement

Direct and residual phosphorus effects on grain yield-phosphorus uptake relationships in upland rice on an ultisol in West Africa

Phosphorus (P) deficiency is a major constraint to crop production on highly weathered, low-activity clay soils in the humid zone of West Africa. Past research suggested a linear relationship between grain yield and P uptake over a range of fertilizer P applied to upland rice cultivars. However, there is lack of information on how these relationships are affected by the long-term fertilizer P effects, although such information is needed for developing P management strategies because phosphate fertilization effects last for several seasons. Results from a long-term field experiment (1993-1998) conducted to determine the response of four improved upland rice cultivars to fertilizer P (0, 45, 90, 135 and 180 kg P ha-1) applied only once in 1993 and to its residues in 1994, 1995, 1996 and 1998, were used to determine grain yield and P uptake relationships. The soil at the experimental site, in the humid forest zone of Côte d'Ivoire (West Africa), was an Ultisol with acidic pH and low in available P. Significant linear relationships (R varying between 0.796 and 0.956) were observed between grain yield and total P uptake for each of the crops grown during 1993-1998. The results indicate that P uptake based models can be used to determine P requirements of rice cultivars under direct and residual P

Effects of parathion and malathion on transformations of urea and ammonium sulfate nitrogen in soils

A study of the effects of malathion and parathion applied at 10 and 50 g/g of soil on transformations of urea and (NH4)2SO4–N in a sandy loam showed that the insecticides retarded urea hydrolysis as well as nitrification of urea and (NH4)2SO4–N. At 50 parts/106 rate of the insecticides, inhibition of urea hydrolysis ranged from 44 to 61% after 0.5 week and from 7 to 21% after 3 weeks of application. The insecticides inhibited the conversion of NH4 + to NO2 – without appreciably affecting the subsequent oxidation of NO2 – to NO3 – –N. This resulted in accumulation of higher amounts of NH4 +–N in soil samples treated with ammonium sulfate or urea N. The results suggest that transformations of urea and NH4 + fertilizers in soils may be influenced by the amount of organophosphorus insecticide present and this may affect plant nutrition and fertilizer use

Effects of nitrogen on growth, and nitrogen and phosphorus uptake in tops and roots of sorghum grown in an Alfisol and a Vertisol

A greenhouse pot experiment was conducted to study the effects of added nitrogen (0, 10, 25, 50 and 100 mg N kg–1 soil) on dry matter production, and N and P uptake in tops and roots of sorghum (cv CSH6) grown in a Vertisol and an Alfisol for 42 days at field capacity soil moisture content. More dry matter accumulated in the tops and roots of sorghum growing in the Alfisol than in the Vertisol. This resulted in higher N and P uptake. Top dry weight responded to N application up to 50 mg N kg–1 soil, whereas the root weight increased at N application up to 25 mg N kg–1. Ratios of root dry weight to total plant dry weight and N uptake in roots/total N uptake were similar in the two soils. Ratio of P uptake in roots to total P uptake was higher in Alfisol than in Vertisol. This result was attributed mainly to higher ratio of P content in roots compared to tops in the Alfisol

Mineralization of biuret nitrogen in soil

Study of the mineralization of biuret N under aerobic and anaerobic conditions in a sandy loam showed that higher amounts of mineral N accumulated under anaerobic incubation than under aerobic conditions. Under waterlogged incubation, 46.8% of the 100 ppm biuret N was mineralized while under aerobic conditions only 18.3% of biuret-N was converted into mineral N during 5 weeks at 30°C. The results of the study bring out slow-release nature of biuret-N

Elemental composition of the rice plant as affected by iron toxicity under field conditions

Iron (Fe) toxicity is a major nutrient disorder affecting the production of wetland rice in the humid zone of West Africa. Little attention has been given to determining the macro‐ and micronutrient composition of rice plants grown on wetland soils where Fe toxicity is present although results from such study could provide useful information about the involvement of other nutrients in the occurrence of Fe toxicity. A field experiment was conducted in the 1997 dry season (January‐May) at an Fe toxic site in Korhogo, Ivory Coast, to determine the elemental composition of Fe tolerant (CK 4) and susceptible (Bouake 189) lowland rice varieties without and with application of nitrogen (N), phosphorus (P), potassium (K), and zinc (Zn). For both Fe‐tolerant and susceptible varieties, there were no differences in elemental composition of the whole plant rice tops, sampled at 30 and 60 days after transplanting rice seedlings, except for Fe. All the other nutrient element concentrations were adequate. Both Fe‐tolerant and susceptible cultivars had a high Fe content, well above the critical limit (300 mg Fe kg‐1 plant dry wt). These results along with our observations on the elemental composition of rice plant samples collected from several wetland swamp soils with Fe toxicity in West Africa suggest that “real”; iron toxicity is a single nutrient (Fe) toxicity and not a multiple nutrient deficiency stress

Nitrification inhibitors from plant resources: a strategy for research

Nitrification inhibitors are chemical ents that inhibit or rather retard nitrification in soil or microbial culture by a sort of family planning among the nitrifying bacteria. Nitrification is referred to as the biological oxidation of ammonium to nitrate via nitrite, effected respectively by Nitrosomonas and Nitrobacter species of the nitrifying bacteria. Nitrification is important for the conversion of ammonium formed from urea and other organic materials and compounds applied to the soil, to nitrate. The nitrate formed is the source of nitrogen (N) nutrition of plants under arable cropping