Heavy Nitrogen Fertilization Research Articles

Functional characterization of the sugarcane (Saccharum spp.) ammonium transporter AMT2;1 suggests a role in ammonium root-to-shoot translocation.

AMMONIUM TRANSPORTER/METHYLAMMONIUM PERMEASE/RHESUS (AMT) family members transport ammonium across membranes in all life domains. Plant AMTs can be categorized into AMT1 and AMT2 subfamilies. Functional studies of AMTs, particularly AMT1-type, have been conducted using model plants but little is known about the function of AMTs from crops. Sugarcane (Saccharum spp.) is a major bioenergy crop that requires heavy nitrogen fertilization but depends on a low carbon-footprint for competitive sustainability. Here, we identified and functionally characterized sugarcane ScAMT2;1 by complementing ammonium uptake-defective mutants of Saccharomyces cerevisiae and Arabidopsis thaliana. Reporter gene driven by the ScAMT2;1 promoter in A. thaliana revealed preferential expression in the shoot vasculature and root endodermis/pericycle according to nitrogen availability and source. Arabidopsis quadruple mutant plants expressing ScAMT2;1 driven by the CaMV35S promoter or by a sugarcane endogenous promoter produced significantly more biomass than mutant plants when grown in NH4 + and showed more 15N-ammonium uptake by roots and nitrogen translocation to shoots. In A. thaliana, ScAMT2;1 displayed a Km of 90.17 µM and Vmax of 338.99 µmoles h-1 g-1 root DW. Altogether, our results suggest that ScAMT2;1 is a functional high-affinity ammonium transporter that might contribute to ammonium uptake and presumably to root-to-shoot translocation under high NH4 + conditions.

Effects of long-term nitrogen application on soil acidification and solution chemistry of a tea plantation in China

In tea (Camellia sinensis) plantation areas, soil acidification mainly results from excessive nitrogen fertilization. However, the proposed theoretical explanations for soil acidification due to nitrogen fertilization are still lacking empirical validation because most studies have used short-term incubation periods or pot experiments. Here, both soil and soil solution samples were taken from a tea plantation field (Ultisol in USDA taxonomy system, or Alisol in WRB taxonomy system) treated using different nitrogen application rates: 0 (N0), 119 (N119), 285 (N285), and 569 (N569)kgNha−1yr−1 for 8 years (2006–2013). Soil pH and the concentrations of the relevant cations and anions were also determined. With no nitrogen fertilization (N0), the surface soil pH decreased from 4.16 to 3.32 after 8 years in the tea plantation. Compared with no nitrogen fertilization (N0), high nitrogen fertilization (N569) significantly decreased the soil pH from 3.32 to 3.15 and 3.67 to 3.35 in the soil at depths of 0–40cm and 40–90cm, respectively. However, the low (N119) and moderate (N285) nitrogen treatments showed non-significant effects upon soil pH. Our results confirm the previous findings that a high nitrogen application rate can accelerate soil acidification in a tea plantation, and that the subsoil is particularly susceptible to acidification after heavy nitrogen fertilization. Soil acidification also significantly decreased the nutrient base cations Ca2+, Mg2+, and K+ in the soil. Our results suggest that heavy synthetic nitrogen fertilization should be partly replaced with compound or organic fertilizers to mitigate soil acidification and nutrient cation deficiency in tea plantation fields.

東北農研が育成した水稲品種における多肥栽培および直播栽培の収量・品質

農研機構東北農業研究センターが育成した中食・外食用の水稲3品種「ちほみのり」，「萌えみのり」，「えみのあき」における標肥移植栽培，多肥移植栽培，標肥直播栽培，多肥直播栽培の5年間の生産力検定試験の結果を解析した．多肥栽培は標肥栽培と比較して，穂数と1穂籾数が多いために精玄米重が多く，品質は同程度であった．直播栽培は移植栽培と比較して，穂数は多いが，精玄米重が少なく，品質は同程度かやや優れていた．早生品種の「ちほみのり」は，「あきたこまち」と比較して，多肥栽培，および直播栽培において，精玄米重が有意に多く，品質は同程度であった．中生品種の「萌えみのり」は，「ひとめぼれ」と比較して，多肥移植栽培および多肥直播栽培における精玄米重が有意に多く，品質はやや劣っていた．中生品種の「えみのあき」は，「ひとめぼれ」と比較して，多肥移植栽培および多肥直播栽培における精玄米重がやや多く，品質はやや優れていた．これらの結果から，東北農研育成3品種は，多収および低コスト化・省力化が求められる中食・外食向けの米生産に適していると考えられた．本研究の結果とこれまでの多収品種に関する報告との比較を通じて，東北地域における中食・外食向けのさらなる多収品種を育成するためには，1穂籾数を多く，千粒重をやや重くすることが重要であると考察した．

Differential Responses of Nitrifier and Denitrifier to Dicyandiamide in Short- and Long-Term Intensive Vegetable Cultivation Soils

Nitrification inhibitors, such as dicyandiamide (DCD), have been shown to decrease leaching from urea- and ammonium-based fertilizers in agricultural soils. The effect of nitrification inhibitors on nitrifier and denitrifier in short- and long-term intensive vegetable cultivation soils was poorly understood. In this study, the pot trial was conducted to investigate the differential responses of nitrifier (amoA-containing bacteria) and denitrifier (nirK-containing bacteria) to DCD in short-(soil S) and long-term (soil L) intensive vegetable cultivation soils. Quantitative polymerase chain reaction (qPCR) and terminal restriction fragment length polymorphism (T-RFLP) were employed to detect the abundance and composition of amoA- and nirK-containing communities. The results indicated that application of DCD led to a consistently higher NH4+-N concentration during the whole incubation in soil L, while it was quickly decreased in soil S after 21 days. Furthermore, DCD induced more severe decrease of the abundance of amoA-containing bacteria in soil L than in soil S. However, the abundance of the nirK-containing community was not significantly affected by DCD in both soils. Long-term vegetable cultivation resulted in a super-dominant amoA-containing bacteria group and less divergence in soil L compared with soil S, and DCD did not cause obvious shifts of the composition of ammonia-oxidising bacteria (AOB). On the contrary, both amoA- and nirK-containing bacterial compositions were influenced by DCD in soil S. The results suggested that long-term intensive vegetable cultivation with heavy nitrogen fertilization resulted in significant shifts of AOB community, and this community was sensitive to DCD, but denitrifiers were not clearly affected by DCD.

Autoregulation of Nodulation Interferes with Impacts of Nitrogen Fertilization Levels on the Leaf-Associated Bacterial Community in Soybeans

The diversities leaf-associated bacteria on nonnodulated (Nod(-)), wild-type nodulated (Nod(+)), and hypernodulated (Nod(++)) soybeans were evaluated by clone library analyses of the 16S rRNA gene. To analyze the impact of nitrogen fertilization on the bacterial leaf community, soybeans were treated with standard nitrogen (SN) (15 kg N ha(-1)) or heavy nitrogen (HN) (615 kg N ha(-1)) fertilization. Under SN fertilization, the relative abundance of Alphaproteobacteria was significantly higher in Nod(-) and Nod(++) soybeans (82% to 96%) than in Nod(+) soybeans (54%). The community structure of leaf-associated bacteria in Nod(+) soybeans was almost unaffected by the levels of nitrogen fertilization. However, differences were visible in Nod(-) and Nod(++) soybeans. HN fertilization drastically decreased the relative abundance of Alphaproteobacteria in Nod(-) and Nod(++) soybeans (46% to 76%) and, conversely, increased those of Gammaproteobacteria and Firmicutes in these mutant soybeans. In the Alphaproteobacteria, cluster analyses identified two operational taxonomic units (OTUs) (Aurantimonas sp. and Methylobacterium sp.) that were especially sensitive to nodulation phenotypes under SN fertilization and to nitrogen fertilization levels. Arbuscular mycorrhizal infection was not observed on the root tissues examined, presumably due to the rotation of paddy and upland fields. These results suggest that a subpopulation of leaf-associated bacteria in wild-type Nod(+) soybeans is controlled in similar ways through the systemic regulation of autoregulation of nodulation, which interferes with the impacts of N levels on the bacterial community of soybean leaves.

Community shifts of soybean stem-associated bacteria responding to different nodulation phenotypes and N levels

The diversity of stem-associated bacteria of non-nodulated (Nod(-)), wild-type nodulated (Nod(+)) and hypernodulated (Nod(++)) soybeans were evaluated by clone library analyses of the 16S ribosomal RNA gene. Soybeans were dressed with standard nitrogen (SN) fertilization (15 kg N ha(-1)) and heavy nitrogen (HN) fertilization (615 kg N ha(-1)). The relative abundance of Alphaproteobacteria in Nod(+) soybeans (66%) was smaller than that in Nod(-) and Nod(++) soybeans (75-76%) under SN fertilization, whereas that of Gammaproteobacteria showed the opposite pattern (23% in Nod(+) and 12-16% in Nod(-) and Nod(++) soybeans). Principal coordinate analysis showed that the bacterial communities of Nod(-) and Nod(++) soybeans were more similar to each other than to that of Nod(+) soybeans under SN fertilization. HN fertilization increased the relative abundance of Gammaproteobacteria in all nodulation phenotypes (33-57%) and caused drastic shifts of the bacterial community. The clustering analyses identified a subset of operational taxonomic units (OTUs) at the species level in Alpha- and Gammaproteobacteria responding to both the nodulation phenotypes and nitrogen fertilization levels. Meanwhile, the abundance of Betaproteobacteria was relatively constant in all libraries constructed under these environmental conditions. The relative abundances of two OTUs in Alphaproteobacteria (Aurantimonas sp. and Methylobacterium sp.) were especially sensitive to nodulation phenotype and were drastically decreased under HN fertilization. These results suggested that a subpopulation of proteobacteria in soybeans is controlled in a similar manner through both the regulation systems of plant-rhizobia symbiosis and the nitrogen signaling pathway in plants.

Nitrification in polluted soil fertilized with fast- and slow-releasing nitrogen: A case study at a refinery landfarming site

The nitrifying activity and the effect of fertilization with urea and methylene urea were studied in a landfarming site. The site has been operative over 20 years and maintained by heavy nitrogen fertilization. The landfarming soil contained 4–6% (w/w) oil. The nitrate accumulation was 20–50 mg NO 3-N day −1 kg −1 observed after methylene urea fertilization of 889 g N m −2. Nitrification ex situ (in laboratory conditions) was 8.8 mg NO 3-N day −1 kg −1 in the presence of 380 mg kg −1 NH 4 +-N. The half-saturation concentration of nitrification was more than 200 mg NH 4 +-N kg −1. The results show that nitrification was active in soil with high oil concentration. Urea fertilization of 893 g N m −2 caused an increase of soil NH 4 +-N concentration up to 5500 mg kg −1 and pH > 8.5. This led to inhibition of nitrification, which persisted after NH 4 + concentration decreased below 200 mg NH 4 + kg −1.

Nitrous oxide flux from a tea field amended with a large amount of nitrogen fertilizer and soil environmental factors controlling the flux

Nitrous oxide (N2O) is one of the main greenhouse gases, and accurate estimation of the N2O flux from fertilized arable land is required. It is known that acidic tea field soil displays a higher N2O production activity than neutral arable soil and that tea fields could be a major source of N2O. Therefore, N2O fluxes from four plots (Std, 2N, 2Ca and −Ca plots) in a tea field that had been subjected to different conditions of fertilizer management were measured using the closed chamber method over a period of two years, and the relationships between the N2O flux and soil environmental factors were analyzed. The amounts of nitrogen fertilizer and liming material (dolomite) applied to the Std plot were 600 kg N ha−1 y−1 and 1,500 kg ha−1 y−1, respectively. The amount of nitrogen fertilizer applied to the 2N plot was two-times larger than that applied to the Std plot and corresponded to the conventionallevel in Japanese tea fields. The soil was acidified due to heavy nitrogen fertilization in the 2N plot. The 2Ca plot was amended with two-times the amount of liming material of the Std plot and in the −Ca plot no liming material was applied. There were significant differences among the N2O fluxes from the plots, and the highest value of N2O flux was 8.785 mg N m−2 h−1 in the 2N plot. Annual emission rate and emission factor of N2O in the 2N plot were 25.22 kg N2O-N ha−1 and 2.10%, respectively. Both long-term heavy nitrogen fertilization and subsequent soil acidification possibly enhanced the N2O flux from the tea field. The N2O flux from the tea field showed temporal variations, namely the N2O flux was relatively low from December to March possibly due to the low soil temperature and it increased gradually after March as the soil temperature increased over 10°C. The N2O flux reached the first major peak in July, decreased transiently in August presumably due to the drying of soil, increased again and reached the second peak in September or October, and then decreased after November. Multiple linear regression analysis of the relationships between the N2O flux and soil environmental factors indicated that the N2O production activity was significantly related to the N2O flux from the tea field. The N2O production activity showed temporal variations corresponding to the temporal variations of the N2O flux.

Rhizosphere Phosphorus Depletion Induced by Heavy Nitrogen Fertilization in Forest Nursery Soils

AbstractThe cause of N‐induced P deficiency in white spruce [Picea glauca (Moench) Voss] seedlings was investigated in a greenhouse pot trial testing factorial additions of ammonium nitrate (AN) and phosphoric acid (PA) to root zone and root‐free compartmentalized soils. Plant growth was significantly improved by combined N and P topdressings during the growing season. However, N‐only fertilization induced P deficiency symptoms and reduced biomass and P status in shoots, demonstrating an apparent N antagonism on P. Phosphorus availability in this treatment also was 35% lower in the rhizosphere soil than in the root‐free bulk soil, reflecting rhizosphere P depletion. Soil acidity and Al activity were increased most by AN‐only applications, probably contributing to reduced P availability. A diagnosis of induced Al toxicity by N fertilization based on plant analysis data was supported by symptoms of root injury. Phosphorus capture by ion‐exchange resin bags at the base of the pots was lower than that of N with combined N‐P applications, suggesting rapid fixation and low mobility of P in the soil compared with N. Nitrogen‐induced rhizosphere P depletion in this nursery soil was attributed to restricted root development of seedlings due to Al toxicity, reduced P availability by Al‐phosphate precipitation, and low P replenishment because of slow diffusion from the bulk soil. Topdressing with both PA and AN increased P availability in the rhizosphere (320 mg kg−1), reduced soil extractable Al by 40% compared with AN‐alone treatments, and increased plant uptake of N and P by 270%, resulting in positive N × P interactions on plant growth.

Partitioning of nitrogen from biological fixation and fertilizer in Phaseolus vulgaris

Nitrogen uptake, distribution and remobilization in the vegetative and reproductive parts of the plant were studied in bean (Phaseolus vulgaris L.) cultivars Negro Argel and Rio Tibagi inoculated with either Rhizobium strain C05 or 127 K‐17. Greenhouse grown plants were supplied with 2.5 mg N (plant)−1 day−1 as KNO3 or K15NO3 and the relative contribution to total plant nitrogen of mineral and symbiotically fixed nitrogen was determined. Control plants included those entirely dependent on fixed nitrogen as well as uninoculated plants supplied with 10 mg N (plant)−1 day−1. No differences were observed between inoculated treatments in total nitrate reductase activity and in the amount of mineral nitrogen absorbed, but there were considerable differences in the contribution of fixed nitrogen. Nitrogen fixation supplied from 58 to 72% of the total nitrogen assimilated during the bean growth cycle and the symbiotic combinations fixed most of their nitrogen (66 to 78% of total nitrogen) after flowering. Maximum uptake of mineral nitrogen was in the 15‐day‐period between flowering and mid‐podfill (47 to 58% of total mineral nitrogen). Nitrogen partitioning varied with Rhizobium strains, and inoculation with strain C05 increased the nitrogen harvest index of both cultivars. Applied mineral nitrogen had a variable effect and in cv. Negro Argel was more beneficial to vegetative growth, resulting in smaller nitrogen harvest indices. Seed yield was not increased by heavy nitrogen fertilization. In contrast, cv. Rio Tibagi always benefited from nitrogen applications. Among the various nitrogen sources supplying the grain, the most important one was the fixed nitrogen translocated directly from nodules or after a rapid transfer through leaves, representing from 60 to 64% of the total nitrogen incorporated into the seeds.

Studies on the Influence of Cultural conditions to Rice Quality, especially Amount of Protein Content in Rice Kernel

In this studies we investigated influence of cultural conditions to amount of protein content in rice ripened kernel. The results are summarized as follows; 1) Conditions of many panicle formation per square meter, such as heavy nitrogen fertilization and dense planting, induced to low percentage of ripened grain, and grow small kernels. 2) Injury of root and leaf-blade, and lodging, also induced low percentage of ripened grain and small kernels. 3) Above different conditions grow as same as small kernels, and small kernels are usually protein rich kernels in this studies. The correlation coefficient between net solidity of rice kernel and amount of protein content of kernel was r=-0.903**. 4) According to our previous report, early variety usually formed protein rich kernels than late variety.

Título en español.

Se aplicaron diferentes niveles de nitrato (NO3) y ácido giberélico (AG) a plantas de caña de azúcar, con el propósito de aclarar las interrelaciones de estos compuestos que afectan el crecimiento, la producción de azúcar y la actividad enzimática. Como ya se sabía que tanto un nivel bajo de NO3 como de AG en una aplicación foliar aumentan individualmente la síntesis de la sacarosa, la aplicación de estos compuestos en forma combinada sugería las siguientes preguntas: 1, ¿Hasta qué grado puede reducirse el NO3 sin que la disminución del crecimiento afecte los aumentos de la sacarosa? 2, ¿Hasta qué punto un aumento en la concentración del NO3 puede afectar la acción favorable de la aplicación del AG? 3, ¿Existe acaso una combinación de AG y NO3, a una concentración alta, cuyos efectos permitan simultánemente tanto un aumento en el tonelaje como en la síntesis de la sacarosa? Se trataron plantas saludables de 12 semanas de sembradas y cultivadas en arena, durante un período de 5 semanas. Se aplicaron tres niveles de NO3 (0, 5 y 30 meq/l) y de AG (en forma de aspersión foliar con soluciones al 0, 0.01 y 0.10 por ciento) en un experimento de diseño factorial de 3 X 3. Los resultados fueron los siguientes: 1. Los pesos húmedos indicaron que tanto el NO3 como el AG causaron un aumento moderado en el crecimiento. Se obtuvo el mayor rendimiento al combinarse el NO3, a una concentración alta, con el AG a una intermedia. La concentración intermedia de AG estimuló el alargamiento de los entrenudos, sin alterar el grosor de la caña. El AG a un nivel alto causó un alargamiento excesivo, y el debilitamiento y encamado ocasional de las plantas. 2. Los aumentos en el crecimiento inducidos por el NO3 cesaron en presencia de un nivel alto de AG. La eliminación del NO3 no impidió seriamente el crecimiento siempre que se aplicó el AG. El crecimiento de las plantas que sólo se trataron con AG fue comparable al de las tratadas con un nivel alto de NO3, pero sin el AG. 3. La eliminación del NO3 estimuló considerables aumentos de sacarosa, tanto en la hoja como en los tejidos tiernos donde se acumula. Al aumentarse el NO3, aumentó a su vez la síntesis de las cetosas totales pero esto causó una reducción del contenido de sacarosa. El AG produjo aumentos significativos de sacarosa en los tejidos donde se acumula cuando se suministró poca cantidad del NO3. Sin embargo, los aumentos de sacarosa inducidos por el AG no pudieron compensar las pérdidas de ésta causadas por un nivel alto de NO3. 4. El tratamiento más favorable para estimular el crecimiento y la producción de azúcar fue la combinación de un nivel bajo de NO3 y un nivel intermedio de AG. Esto indujo un crecimiento moderado y un aumento mayor de sacarosa. 5. La ATP-asa y la fostatasa foliares fueron muy estimuladas por el NO3. El AG a una concentración alta aminoró los efectos causados por el NO3. 6. Una fuerte interacción del NO3 y el AG afectó tanto las enzimas hidrolíticas como los oxidantes en los tejidos tiernos. También fueron afectadas la fosfatasa, la ATP-asa, la peroxidasa y la oxidasa de polifenol. 7. El NO3 aumentó en grado sumo el contenido de proteína del tejido tierno, pero el AG apenas tuvo efecto alguno. El AG estimuló el crecimiento y la formación de azúcar sin que se registraran los grandes cambios en las proteínas que son característicos de los tratamientos con NO3. Se discute la aplicación práctica que puede hacerse de los resultados obtenidos en las pruebas con NO3 y AG. Se cree que la aplicación del AG debe posponerse hasta después que se abone a un nivel alto de nitrógeno, y que su acción no es plenamente efectiva cuando la aplicación se hace simultáneamente con las de los programas corrientes de abonamiento.

Influence of Drainage on the Growth of Rice Plant in Rice Field : II) Relation between irrigation methods and the growth and yield of rice at various levels of nitrogen fertilization and sowing density

The experiment was conducted to evaluate the effect of various irrigation methods on the growth and yield of rice plant in direct sowing cultivation. The field experiment involving three irrigation treatments, two levels of nitrogen fertilization and four levels of sowing density was established in 1962. Because of practical consideration in applying irrigation water, the irrigatin treatments were located in separate block. The nitrogen and sowing treatments were randomized in a split plot design with nitrogen levels as the main plot and sowing density as subplot. The replication was three. The irrigation treatments involed three plots of early irrigation, late irrigation and interval irrigation. In the early irrigation plot, the water had been kept 5 cm deep since early tillering stage of rice plant. The late irrigation plot was kept dry during tillering stage of plant, and irrigation was begun when the plant reached young ear formation stage. The interval irrigation plot was applied 5 cm of water in depth at an interval of 7 days. The nitrogen plots were divided into two, that is 0.6 kg and 1.2 kg-N per are. The levels of sowing density were 10, 25, 50 and 100 hills per m2. The results obtained are as follows. 1) The amounts of NH3-N in soil in the plots of both late irrigation and interval irrigation were smaller than that in the plots of early irrigation. The amounts of NO3-N in soil generally were trace, except the case of late irrigation kept dry through the tillering period of plant. It seems that the decrease of available nitrogen in the late irrigation and interval irrigation plots are caused by the leaching of NO3-N and the denitrification resulting from the alternation of oxidation and reduction of soil by irrigation and rainfall. 2) The treatments of late irrigation and interval irrigation indicated the increased activity of root, as measured by means of α-Naptylamine, over the early irrigation. The root activity in the high density (100 hills/m2) was lower than that in low density (10 hills/m2). The root weights per unit area in the late irrigation and interval irrigation plots were lighter than that in the early irrigation plot. The treatment of high density indicated the increased weight of root. 3) The grain yields in the late irrigation and interval irrigation plots were about 10 % less than that in the early irrigation plot, while there was little difference between the former two. The grain and total weight at harvest generally increased as the sowing density increased. The highest yield of all treatments was obtained in the plot with early irrigation, heavy nitrogen fertilization and high sowing density combined. The yield data obtained were fitted with rectangular hyperbola equation of the general form: y=x/a+bx where y is the estimated grain or total weight at harvest in kg per are, x is sowing density, and a and b is a coefficient, respectively. The values of two coefficients in both the late irrigation anb interval irrigation are higher than that in the early irrigation, and heavy dose of nitrogen decreased the values of coefficients. It is therefore concluded that the early irrigation method with heavier nitrogen fertilization and higher sowing density is effective for getting high yield of rice.

Studies on the Nutrition of Rice Plant with Reference to the Occurrence of the So-called "Akagare" Disease : VI. Changes in the growth, nutrients-absorption and metabolism in plant as influenced by the excessive supply of ferrous iron

In order to make clear the relation between the excessive ferrous iron and the occurrence of Akagare, several experiments were carried out. Results of experiments are as follows: 1) On adding surplus Fe++ to the culture solution, tiny blackish browh spots appeared on the lower leaves. These leaves, subsequently, turned brown or reddish brown and died off. Heavy nitrogen fertilization, lack of phosphorus and potassium, concomitant addition of butyric acid, and low pH of soution intensified such effect of Fe++ as described above. 2) Discoloration of leaves due to surplus Fe++ occurred most severely at the vigorously tillering stage, and more severely at the booting stage of the plant. At the same time severe brown discoloration of grain due to surplus Fe++ occurred at the stage of heading and flowering. 3) The yield of rice was decreased extremely by the addition of surplus Fe++ at the booting and early ripening stage, and to a less extent at the vigorously tillering stage. 4) Resistance to the surplus Fe++ which showed a close relationship with the accumulation of starch at the base of shoot was generally parallel to the resistance to Akagare in rice varieties. 5) Nutrients absorption was inhibited in the order P2O5, MnO>K2O, SiO2>NH4-N, CaO. Respiratory rate and cytochrome oxidase 'activity of root were retarded by surplus Fe++, while respiratory rate and peroxidase activity of leaf blade were promoted, irrespective of the decrease of cytochrome oxidase activity. Both the content of protein-N of leaf and the content of total sugar and starch of shoot were decreased, while the content of soluble-N was increased by Surplus Fe++. 6) The fact that quite the same tendency was observed as to the changes in respiration and metabolism with both the plants subjected to excessive Fe++ in this work and those affected by Akagare in previous works, suggests that the excessive ferrous iron has some relationship with the occurrence of Akagare.

A lysimeter investigation of nitrogen gains and losses under various systems of covercropping and fertilization, and a discussion of error sources

The Results in Brief The net gain or loss of soil nitrogen was studied in lysimeters at Riverside for ten years under four series of treatments: (1) fall applications of cereal straw (5,000 pounds per acre); (2) a mustard winter covercrop; (3) purple-vetch winter covercrop; (4) sweet-clover winter covercrop. In each series, one lysimeter was given no fertilizer, one 100 pounds, and one 200 pounds of nitrogen per acre per year as nitrate. A summer-harvested crop (first barley, later Sudan grass) was grown in all lysimeters. Total nitrogen and organic matter in the soil at the outset and at five-year intervals, amounts of nitrogen removed by cropping and leaching, and amounts added in seed, rain, irrigation water, and fertilizer were recorded. Unaccounted-for net losses of nitrogen, thought to be due to gaseous volatilization, amounted to more than 60 pounds per acre per year with a mustard covercrop when 200 pounds of nitrogen per acre was added in fertilizer. Similar losses occurred with cereal-straw applications and 200 pounds of nitrogen. Net gains of nitrogen when legume covercrops were grown without fertilization amounted to about 150 pounds per acre per year. These net gains were progressively reduced when 100 and 200 pounds of nitrogen per acre per year was added in fertilizer. Net gains of nitrogen due to nonsymbiotic fixation amounted to 48 pounds per acre per year when dry cereal straw was applied without fertilization; they amounted to 40 pounds per acre per year when a mustard covercrop was grown without fertilization. Average loss of nitrogen through leaching varied from 4 to 88 pounds per acre per year. It was highest when no winter covercrop was grown and with heavy nitrogen fertilization, considerably higher with legume covercrops than with mustard. Most of the losses occurred in years of heavy rainfall or when rain fell just after an irrigation, since irrigation was designed to just meet the water requirements of the crops grown. The nitrogen requirements of Sudan grass—about 125 pounds of nitrogen per acre per year for maximum yields—were fully met through the nitrogen fixed by legume covercrops: yields were not increased by nitrogen fertilizer when legume covercrops were grown, although the fertilizer increased the growth of the legumes. The nitrogen added in cereal straw (22 pounds per acre per year), in rain and irrigation water (7 pounds), and by nonsymbiotic fixation (48 pounds) was not enough to meet the requirements of the Sudan grass. These results indicate that high-level nitrogen fertilization is wasteful. If much more nitrogen is applied than the crops need, substantial amounts will be lost by gaseous volatilization and by leaching, fixation will be reduced, and luxury consumption of nitrogen by crops may occur without benefit to yield or quality. Therefore, greatest nitrogen economy will be achieved when nitrogen is maintained at the lowest possible point consistent with satisfactory crop performance.