Reduced Soil Conditions Research Articles

Nitrate Reduction to Ammonium in Anaerobic Soil

AbstractKnowledge regarding the pathway and soil conditions necessary for NO3‐ Conversion to NH4+ and organic N, a process which conserves soil N, is limited. The influence of rice straw (2.5 mg C/g soil), methanol (1.0 mg C/g soil), and glucose (1.0 mg C/g soil) on the fate of 100 µg/g 15N‐labelled NO3‐‐N was studied in Crowley silt loam. The fraction of the added NO3‐‐N in the NO3‐, N2, NH4+, and organic N forms was determined after 4‐day incubations under an Ar atmosphere at 30°C. In glucose‐amended soil 9 and 19% of the applied NO3‐‐N was recovered as NH4+‐N and organic N, respectively. A 1‐day preincubation with glucose (0.5 mg C/g soil) before the 4‐day incubation with added NO3‐ and glucose increased labelled NH4+‐N and organic N recovery to 36 and 34% of the added NO3‐‐N, respectively. The corresponding values for rice straw‐ and methanol‐treated soil and soil containing no added energy source were each less than 5%.Nitrate‐N reduction to NH4+‐N increased to 20.5% after a 4‐day incubation when soil with no C amendment was incubated under Ar for 20 days before NO3‐ addition. The redox potential was −260 mV upon NO3‐ additionTransformation of significant amounts of NO3‐ to NH4+ and organic N required intensely reduced soil conditions. The reaction was apparently not suppressed by NH4+. Evidence indicated that NO3‐ was reduced to NH4+ by a nonassimilatory pathway in which NO3‐ functioned as a terminal electron acceptor.

The Effect of Large Applications of Manure on Movement of Nitrate and Carbon in an Irrigated Desert Soil

AbstractFeedlot manure was applied in the field at rates of 0, 45, 90, 180, and 360 metric tons/ha to a Holtville clay under irrigated conditions. Holtville clay is a soil with restricted internal drainage. Ceramic cups were installed at various depths in the soil profile to monitor the movement of manganese, nitrate, and soluble organic carbon.The manure greatly increased the amount of soluble organic carbon in the soil solution. An increase in the manure application rate to 180 or 360 metric tons/ha increased the nitrate in the soil solution at 20 and 40 cm, but there were only small differences at 80 and 140 cm. The lack of movement of nitrate to the 80‐cm depth for the high rates of manure application appeared to be due to denitrification, because high nitrate levels were present in the surface soil and sufficient water was applied to leach to this depth. Nitrate leaching was less when manure was applied annually than when it was applied only the first year. Less movement of nitrate to the 80‐cm depth in treatments receiving manure annually seems to be the result of denitrification caused by the higher level of soluble organic carbon. The application of manure did not result in reducing conditions at 20 cm under regular irrigation as measured by redox potential, but the double irrigation schedule caused soil reducing conditions at 20 cm. At 80 cm, manganese in the soil solution was inversely correlated to nitrate level.

Effect of Eh and pH on the Dissolution of Strengite

THE reduction of strengite (FePO4·2H2O) to more soluble (Fe2+)x (Fe3+)y·(PO4)z compounds is one possible source of the frequently reported1–4 higher concentrations of soluble P found in reduced soil conditions as compared with well aerated soils. To investigate this theory in more detail the dissolution of crystalline strengite was followed in controlled pH and redox (Eh) conditions.

Histogenetical Studies on Cortical Disintegration in Rice Roots

Several lines of investigation have been carried on the formation of lysigenous lacunae of rice plant roots. The results obtained so far, however, do not agree with each other on the mechanism of formatlon and physiological significance of the lacunae. It was reported by many investigators that the development of the lacunae of rice plant roots growing under anaerobic soil conditions was remarkable as compared with that of aerobic soil conditions. It was assumed that oxygen needed for root respiration would be supplied mainly by leaves via stems and lysigenous lacunae when the rice plant was kept in anaerobic soil. On the other hand, an investigator asserted that the physiological role of lysigenous lacunae of rice plant roots should be reexamined from that the formation of lysigenous lacunae had relations with the development of lateral roots, that the fomation of lateral roots in the soil of paddy field was generally accelerated when it was in oxidative state and that the development of lacunae, on the contrary, was slowed down when the soil was reductive. In an attempt to throw the light on the differences observed in these works, the histogenesis and the changes in the volume of lacunae and lateral roots were studied in rice seminal roots growing under two kinds of soil conditions in oxidation-reduction potentials. The phenomenon of cortical disintegration may be consisted of two phases, emergence and enlargement. With the exception of roots, 2 days old growing under reductive soil conditions, the emergence of cortical disintegration was always observed with the primordia of lateral roots. In two days roots growing under reductive soil conditions, the emergence of cortical disintegration was found, but the initiation of lateral root primordia was observed nowhere. While the enlargement of cortical disintegration was noticeable more distinctively in the roots growing under oxidative soil conditions (hereinafter referred to as O) than in the roots growing under reductive soil conditions (hereinafter referred to as R) for 4 days after seeding. Though there were little differences in the density of lateral roots and the primordia on the same aged parts (e. c. was 0.9 cm length from root base in O and 0.6 cm in R), for 4 days after seeding O exceeded distinctly R in the volume of lateral roots per centimeter and the growth of lateral roots in length of which the longest lateral roots represented of each region abovementioned. On and after the 4th, R was superior to O in the percentages of lacunae, the volume of lateral roots and the growth of lateral root in length. On the basis of such results, it was assumed that the emergence of cortical disintegration and the initiation of lateral roots have a close relationship with each other in time and position, and the enlargement of cortical disintegration was restricted by the velocity and the volume of the growth of lateral roots. Anyhow, the results of this experiment seem to indicate that whether the development of cortical disintegration will become well in R or O, depends mainly on the growth of lateral root in volume or velocity. A difference, as previously stated, in observations among investigators with refference to the extent of the development of cortical disintegration in R and O may be consolidated by these results.

Cultivated Rice Varieties viewed from Root Characters : (V) Phosphorus compounds in roots and varietal resistabilities against soil reduction

As already reported by many researchers, varietal differences of the resistability against soil reduction are mainly caused by the oxidizing power of roots, that is, by the energy releasing power for the maintenance of metabolic activities. Under the reductive soil conditions, it was also pointed out that the fall of the root respiration occured, accompanying with the degradation in the phosphorylation processes of sugars in roots. Therefore it is assumed that the more resistant, varieties may produce the organic phosphates much more in contrast to the inorganic ones, under both natural and abnormal conditions. From these viewpoints, the authors determined varital differences of organic and inorganic phosphorus compounds in roots, both quantitatively and qualitatively, in order to show the relationship between their conetnts and the varietal resistabilities. The experiments composing the studies and the main results obtained were as follows: 1) The absorption of 32p measured by the counting method (Tab. 1): The more resistant variety (Norin 69) absorbed the radioactive element much more in roots than the less resistant one (Norin 36), at both the 6 th an 9 th leaf stages. It was also ascertained under abnormal conditions. The abnormal condition means the plots which were treated whith hydroquinon in order to deprive the plants and the medium of oxygen. 2) Phosphate contents in roots determined by chemical analyses (Tab. 2 & Fig. 1): Contents of both organic and inorganic phosphates were more or less larger in the roots of the more resistant variety (Norin 37), as compared with the less resistant one (Norin 41), under both conditions mentioned above. It was almost always assured at every growth stages selected. Besides the ratios of the organic phosphates to the inorganic ones because higher in the normal plants than in those injured by the chemical. It was especially true in the more resistant variety (Fig. 2). 3) Organic phosphates found by the qualitative analysis (Fig. 3): The paper chromatographic method applied to the acid soluble organic phosphates in roots showed that 3-phosphoglyceric acid was never recognizable in both varieties treated. From this fact, it was inferred that some of organic phosphates to be translocated migth be vanished or not synthesized when the root respiration was checked. 4) Anatomical observations of roots treated with hydroquinon (Fig. 4): Epidermis and its neighbouring tissues wer discolored yellow or brown. It was also alike in stele, of which strands seemed to be stoppered. These phenomena suggest that nutrients migration from root to top may be largely disturbed.

Researches on the Technical Improvement of Rice Culture on Ill-Drained Fields.

(1) 31 samples of "Akagare" paddy fields and 17 of ordinary paddy fields were examined comparatively. Nitrogen and humns contents, effects of the drying treatment of soil, soil reduction, obsorptive coefficients of K2O or NH3-N of each soils ete. were measured. As the results, we found that the factors inducing the Akagare disease would be a poor natural supply of potassium, abundant humus contents in the ill-drained fields, want of ferric substances in the surface soil, excess of ammonium nitrogen, deficiency in oxygen, promoted reduction of Eh value, harmful substances such as organic acid (butyric acid), ferrous compounds, or hydrogen sulphide in the soil. 13 different types of Akagare paddy field were classified according to the factors ascribable. (2) For the purpose of studying the influences of reductive soil conditions on the plant growth, pot experiments were carried out. In the non-aerated plots, the surface of the soil in the pots were covered with olive oil at various stages of plant growth. In the plot II, the soil being covered with oil during the tillering stage, symptoms of "Akagare" disease were found on the upper parts of leaf-blade, and contents of total-N, Fe++ and SO3 in the plant were very much in comparison with, those in the cortrol plot plants, while K2O/N ratio was lower. In the plots IV or V, covered duriug from the ear-forming to the heading stage, the plants grew normally. (3) Influences of harmful substances such as H2S, butyric acid, or ferrous compounds on the vitality of roots and the nutrient absorption, were investigated by a solution culture experiment. Actual injuries of those harmful aubstances added to the solution were observed to be as follows: (a) Prohibition in elongation of roots and in tillering. (b) Decline in water absorption and in consumption of O2 of the roots. (c) Hindrance of absorption of nutrients such as K2O and NH3-N. Consumption in the roots occurred remarkably at the tilleriug and the ear-forming stages, respectively. Symptoms of "Akagare" disease were observed clearly at the tilleriug stage by applying H2S (60 p.p.m) and butyric acid (1/50 N) to the solution. Nutrieut absorption and vitality of the roots recovered 2 to 3 weeks after the removal of those harmful substances from the solution.