Atmospheric nitrogen fixation by photosynthetic microorganisms in a submerged Philippine soil

Photosynthetic nitrogen-fixing microorganisms help maintain the nitrogen level of soil in rice paddies when environmental factors favor the growth of microorganisms. Our studies showed that blue-green algae in particular have a significant role in nitrogen-fixation in light. The most active nitrogen-fixation by microorganisms occurred in the soil shortly after it had been submerged under light. The longer the submergence, the less nitrogen microorganisms were fixed. In a greenhouse experiment, the fixed nitrogen appeared not to be immediately available to the rice plant. The amount of nitrogen that can be fixed in the field by nitrogen-fixing microorganisms in paddy water was estimated using the acetylene reduction method during the rice-growing period. The amount of nitrogen fixation by these microorganisms is not sufficient to account for the amount of nitrogen uptake by rice during the rice-growing period.     

Changes in some enzyme activities and the nicotinamide nucleotide coenzymes in barley seedlings during vernalization

Respiratory metabolism was investigated by determining the following enzyme activities and nicotinamide nucleotide coenzyme contents in barley shoots (Hordeum vulgare L., var. Akashinriki) during vernalization : glucose-6-phosphate dehydrogenase, phosphoglucoisomerase, enolase, isocitrate dehydrogenase, malate dehydrogenase, and glutamic dehydrogenase. The activities of glucose-6-phosphate de hydrogenase and phosphoglucoisomerase in vernalized shoots were slightly lower than those in non-vernalized samples. Malate dehydrogenase activity increased gradually in vernalized shoots and was always higher than in non-vernalized shoots. Activation was found in enolase, isocitrate dehydrogenase and glutamic dehydrogenase after a long vernalization treatment.

The contents of total nicotinamide nucleotide coenzymes increased during the early germination stage in both treatments, then decreased gradually in the succeeding stage.     

Dynamics of microbial biomass nitrogen as influenced by organic matter application in paddy fields

The effects of annual application of rice straw or cow manure compost for 17–20 y on the dynamics of fertilizer N and soil organic N in Gley paddy fields were investigated by using the ¹⁵N tracer technique during the rice cropping season. The chloroform fumigation-extraction method was evaluated to determine the properties of soil microbial biomass under submerged field conditions at the tillering stage before mid-summer drainage, with special reference to the fate of applied NH₄ ⁺-¹⁵N.

The transfer ratios from applied NH₄ ⁺-¹⁵N to immobilized N in soil and to uptake N by rice during given periods varied with the rice growth stages and were affected by organic matter application. The accumulated amounts of netmineralized soil organic N (net-M_j ), immobilized N (I_j ), and denitrified N (D_j ) during the cropping season were estimated to be 14.0–22.5, 6.3–11.2, and 3.4–5.3 g N m^-2, respectively. Values of net-M_j and I_j were larger in the following order: cow manure compost plot > rice straw plot > plot without organic matter application, and their larger increase by the application of cow manure compost contributed to a decrease of the D_j values, as compared with rice straw application.

Values of E _N extra extractable soil total N after fumigation, increased following organic matter application, ranging from 2.1 to 5.4 g N m^-2. Small residual ratios of applied ¹⁵N in the fraction E _N at the end of the given period indicated that re-mineralization of newly-assimilated ¹⁵N through the easily decomposable fraction of microbial biomass had almost ended. Thus, the applicability to paddy field soils of the chloroform fumigation-extraction method was confirmed.     

A study of soil and fertilizer phosphorus intake by Barley plants,using Radioactive tracer technique

Introduction

Phosphorus applied on a phosphate deficient soil, by increasing the root development of the plant, or by stimulating the soil microflora especially in the rhizosphere, may increase the amount of phosphorus which the plant takes up from the soil. This present paper is a report on a pot culture investigation of such an effect of added phosphorus.     

Effects of NPK fertilizer combinations on yield and nitrogen balance in sorghum or pigeonpea on a vertisol in the semi-arid tropics

A long-term experiment was carried out on a Vertisol from 1986 to 1992 to examine the combined effects of NPK fertilizers on yield using sorghum (Sorghum bicolor L. Moench cv. CSH 5) and short-duration pigeonpea (Cajanus cajan L. Millsp. cv. ICPL 87). The fertilizer treatments were as follows: 0 (no fertilization), N (150 kg N ha^-1 ), P (65.5 kg P₂O₅ ha^-1), K (124.5 kg K₂O ha^-1), and all possible combinations (NP, NK, PK, and NPK). In this study we continued this experiment during the period 1993 to 1994 and analyzed the crop yield response to fertilizers and the N balance. The amount of N derived from the atmosphere and fertilizer was estimated by the ¹⁵N natural abundance method and ^l5N isotope dilution method, respectively. A combined application of Nand P fertilizers gave the highest grain yield for the two crops under the 8th and 9th continuous croppings, unlike the application of K fertilizer. The values of total N for the two crops were significantly higher in the NP and NPK plots. These crops took up N mainly from soil. There was a significant positive relationship between the uptake of N_dff and N_dfs by each crop. Pigeonpea or sorghum took up more N from the soil in the N fertilizer plots than in the plots without N, suggesting that soil N fertility was enhanced and the amount of N supplied from soil increased in the plots with consecutive application of N fertilizer for 7 y. Even pigeonpea, which fixes atmospheric N inherently, needed N fertilizer to achieve high grain yield, suggesting that N fixation by the nodules was not always sufficient to meet the N requirements of the crop under these conditions. Although fertilizer N exerted a beneficial effect on plant growth and yield in the two crops, the values of fertilizer N recovery (FNR) by the two crops were considerably low. Therefore, it is suggested that the development of N fertilizer management which could maximize FNR of each crop should be promoted.     

Response of Lowland and Aerobic Rice to Ammonium and Nitrate Supply During Early Growth Stages

Decreasing fresh water availability has intensified the search for alternative rice cultivation systems with reduced water input, but most evidence suggests negative effects on growth of lowland (LL) rice cultivars. Yield in such production systems may be improved by selection of adapted aerobic ‘Han Dao’ (HD) rice cultivars. Lowland and HD rice were compared under sole nitrate or ammonium supply as well as under mixed supply of both nitrogen (N) forms during the seedling and tillering stage; pronounced differences were found in response to the supplied N form. Shoot dry mass (DM) of HD was significantly lower than that of LL under sole and predominant ammonium supply, whereas LL showed the opposite trend, with significantly lower shoot DM under sole-nitrate supply. Nitrogen concentration of LL rice under sole-nitrate supply was significantly lower compared with other treatments at tillering stage. Han Dao rice had a significantly higher potassium (K) concentration than LL rice under sole-nitrate supply, while the opposite result was observed under sole-ammonium supply. At seedling stage, the portion of N that was taken up from nitrate-N varied from 30% to 40% in HD and LL rice in treatments 75N/25A and 50N/50A, while at both growth stages, predominant ammonium supply resulted in a lower portion (20%) of nitrate-derived N in LL than in HD rice. The portion of nitrate-derived N increased at tillering stage (from 40% to 70%). These results further illustrate a synergistic effect of co-provision of nitrate and ammonium on total N fluxes compared with supply of sole nitrate or sole ammonium. It was concluded that the interaction between N form and tiller formation during early growth stages deserves strong attention for the identification of aerobic rice cultivars.     

Timing and Method of 15Nitrogen-Labeled Fertilizer Application on Grain Protein and Nitrogen Use Efficiency of Spring Wheat

ABSTRACT

Grain protein content is one of the most important quality constraints for bread wheat (Triticum aestivum L.) production in eastern Canada. A field experiment was conducted for two years (1999 and 2000) on the Central Experimental Farm, Ottawa, Canada, to study whether split application of nitrogen (N) fertilizer improved grain protein content and nitrogen-use efficiency (NUE). Two cultivars (‘Celtic,’ as N-responsive and ‘Grandin’, as N-non-responsive) were grown using three different N doses and application methods: (1) 100 kg N ha^?1 as NH₄NO₃, soil-applied at seeding with ¹⁵N₂-labeled NH₄NO₃ to microplots, (2) 60 kg N ha^?1 soil-applied at seeding plus 40 kg N ha^?1 foliar-applied at the boot stage with ¹⁵N₂-labeled urea to microplots, and (3) 90 kg N ha^?1 as soil-applied at seeding plus 10 kg N ha^?1 foliar-applied at the boot stage with ¹⁵N₂-labeled urea to microplots. Plants were sampled at heading and maturity. While dry-matter production and grain yields were not affected by the treatments in either year, N application methods influenced tissue N concentration and NUE. In 1999, extended drought stress led to significant yield reduction; in 2000, foliar application of 10 kg N ha^?1 at the boot stage significantly increased grain N concentration when grain protein was under the limit for bread quality, suggesting that later-applied N can contribute to grain protein content. At maturity, the average NUE was 22.3% in 1999 and 34.5% in 2000, but was always greater when all N was applied at seeding (42.5%) than when N was foliar-applied at the boot stage (18.5% to 24.5%). We conclude that application of a small amount of fertilizer N at the boot stage can improve the bread-making quality of spring wheat by increasing grain protein concentration.     

Kinetics of 15N -labelled nitrogen from co-compost made from cattle manure and chemical fertilizer in a paddy field

In order to produce an effective organic fertilizer, cattle manure was cocomposted with chemical fertilizer. And the kinetics of nitrogen uptake by rice plants from the co-compost was investigated using the ¹⁵N labelled co-composts on either cattle manure or chemical fertilizer. As a control, nitrogen kinetics from the mixture of cattle manure and chemical fertilizer without co-composting was investigated. At the early stage, rice growth may have been promoted by co-composting, while, it may have been promoted by the larger N-content of cattle manure at the harvesting stage. The ratios of nitrogen uptake by rice plants and residual nitrogen in soil from the cattle manure and chemical fertilizer were determined by measuring ¹⁵N -atom%. The N -uptake ratios by rice plants from the cattle manure in the co-composted plot were about 2–4 times higher than those from the cattle manure without co-composting. However, the N -uptake ratios from the chemical fertilizer in the co-composted plot were lower than those from the chemical fertilizer without co-composting. The N -content of the rice plants derived from chemical fertilizer without co-composting decreased consistently after 28 d. The nitrogen from chemical fertilizer in the co-compost was absorbed again in the latter period of rice growth. The total nitrogen uptake by rice plants from cattle manure and chemical fertilizer was similar regardless of co-composting. However, co-composting would be advantageous at least· in terms of the following aspects: increase of the N -uptake by rice plants from cattle manure, slow-release ability of nitrogen from chemical fertilizer, decrease of nitrogen loss by denitrification.     

Uptake of 15 trace elements in arbuscular mycorrhizal marigold: Measured by the multitracer technique

The effect of arbuscular mycorrhizal (AM) colonization on the uptake of trace elements in marigold (Tagetes patula L.) was studied using a multitracer consisting of radionuclides of ⁷Be, ²²Na, ⁴⁶Sc, ⁵¹Cr, ⁵⁴Mn, ⁵⁹Fe, ⁵⁶Co, ⁶⁵Zn, ⁷⁴As, ⁷⁵Se, ⁸³Rb, ⁸⁵Sr, ⁸⁸Y, ⁸⁸Zr, and ^95mTc. Marigold plants were grown under controlled environmental conditions in sand culture either without mycorrhizas or in association with an AM fungus, Glomus etunicatum. The multitracer was applied to the pot, and plants were harvested at 7 and 21 d after tracer application. We found that the uptake of ⁷Be, ²²Na, ⁵¹Cr, ⁵⁹Fe, ⁶⁵Zn, and ^95mTc was higher in the mycorrhizal marigolds than in the non-mycorrhizal ones, while that of ⁴⁶Sc, ⁵⁶Co, ⁸³Rb, and ⁸⁵Sr was lower in the mycorrhizal marigolds than in the non-mycorrhizal ones. Thus, the multitracer technique enabled to analyze the uptake of various elements by plant simultaneously. It is suggested that this technique could be used to analyze the effects of AM colonization on the uptake of trace elements by plant.     

Incorporation of nitrogen from urea fertilizer into soil organic matter in rice paddy and cassava upland fields in Indonesia

Incorporation of newly-immobilized N into major soil organic matter fractions during a cropping period under paddy and upland cropping systems in the tropics was investigated in Jawa paddy fields with and without fish cultivation and a Sumatra cassava field in Indonesia. ¹⁵N-labelled urea (¹⁵N urea) was applied as basal fertilizer, and the soil samples were collected after harvest. The percentage of distribution of the residual N in soil from ¹⁵N urea into the humic acids, fulvic acid fraction, and humin were 13.1–13.9, 19.0–20.5, and 53.4–54.3%, respectively, for the Jawa paddy soils, and 14.9, 27.4, and 52.4%, respectively, for the Sumatra cassava soil. These values were comparable to the reported ones for other climatic zones. The percentage of distribution of ¹⁵N urea-derived N into humic acids was larger than that of total N into the same fraction in all the soils. The distribution into the fulvic acid fraction was also larger for ¹⁵N urea-derived N than for total N in the Jawa soils. Humic and non-humic substances in the fulvic acid fraction were separated using insoluble polyvinylpyrrolidone (PVP) into the adsorbed and non-adsorbed fractions, respectively. Less than 5% of the ¹⁵N urea-derived N in fulvic acid fraction was detected in the PVP-adsorbed fraction (generic fulvic acids). The proportion of non-hydrolyzable N remained after boiling with 6 M HCl in the ¹⁵N urea-derived N was 9.4–13.5%, 17.3–26.7%, and 8.4–16.6% for the humic acids, generic fulvic acids, and humin, respectively. The significantly low resistance to acid hydrolysis suggested that the ¹⁵N urea-derived N was less stable than the total N in soil regardless of the fractions of humus.