Dicyandiamide (DCD) as a nitrification inhibitor for rice culture in the United States

Abstract

Efficient nitrogen (N) fertilizer management for paddy rice production is difficult because of potentially high N losses from denitrification, NH₃ volatilization, and leaching. The use of a nitrification inhibitor, by slowing the rate of nitrification of NH₄ ⁺‐N sources prior to flooding, offers the potential to reduce denitrification losses that occur after flooding. Dicyandiamide (DCD) is one such nitrification inhibitor. The objective of this series of studies was to evaluate DCD for its effectiveness as a nitrification inhibitor in paddy rice production across an array of soils, management systems, and climate conditions.

Studies were conducted on fine‐ and medium‐textured soils in Arkansas, California, Louisiana, Mississippi, and Texas. Dicyandiamide was coated onto or formulated with urea (7 or 10% of total N as DCD‐N) and applied either broadcast pre‐plant incorporated or broadcast as a topdress application prior to flooding at the 4‐ to 5‐leaf development stage of the rice plant. These treatments were compared with urea applied either pre‐plant incorporated or in multiple applications timed to the peak N demand periods of rice. An array of N rates were used to model the yield response to levels of N. Similar studies utilizing ¹⁵N‐enriched urea were also conducted.

The studies indicated that use of DCD delayed nitrification and tended to result in rice grain yield increases as compared with urea applied pre‐plant without DCD in drill‐seeded rice; however, proper application of urea in split applications gave more consistent results. In water‐seeded continuously flooded rice culture, use of DCD was advantageous only if the flood was delayed for more than 14 days after urea application. The ¹⁵N‐enriched studies indicated that highest N fertilizer recovery was associated with split topdress urea applications; however, addition of DCD resulted in increased immobilization of fertilizer N and release of soil N.     

Production of Chinese cabbage in relation to nitrogen source,rate, and leaf nutrient concentration

Abstract

Chinese cabbage (Brassica rapa L. Chinensis group) production is expanding in the U. S., and guidelines regarding its production under Western cultural practices are needed. The objectives of this study were to investigate the effects of N source and rate on Chinese cabbage yield, marketability, and wrapper leaf nutrient concentrations, and to estimate the critical wrapper leaf‐N concentration associated with maximum yield and marketability. Chinese cabbage was grown in five sequential plantings using raised‐bed, polyethylene mulch culture with subsurface irrigation on a sandy soil. Nitrogen fertilizer was applied at rates of 0, 67,112, and 157 kg/ha using the following sources: 1) ammonium nitrate. 2) calcium nitrate, 3) urea‐ammonium nitrate solution (Uram, 32% N), 4) urea, and 5) a urea‐calcium solution (18% N). Mature Chinese cabbage wrapper leaf concentrations of P, Ca, and Mg increased with increasing N rate, while leaf‐K concentration decreased. Leaf‐N concentration increased in response to N rate, but was not affected by N source or harvest date. Leaf‐P, K, Mg, and B concentrations were sufficient or high according to established standards, but leaf‐Ca was low. Leaf‐Ca and Mg concentrations were lowest with N sources containing only urea, and highest where at least part of the N was applied as NO₃ ^‐. Chinese cabbage head weight and percentage marketable heads increased as N rate increased. Yield and quality were highest with N sources which contained NO₃ ^‐, and were smallest where N was applied entirely as urea, which may have been due to plant sensitivity to NH₄ ⁺. The critical value of mature cabbage wrapper leaf‐N concentration above which yield or marketability was not limited was estimated to be 36 to 41 mg/g, which agrees well with established standards.     

INFLUENCE OF HIGH TEMPERATURE AND UREA FERTILIZATION WITH N-(N-BUTYL) THIOPHOSPHORIC TRIAMIDE AND DICYANDIAMINDE ON COTTON GROWTH AND PHYSIOLOGY

The objective of this growth chamber study was to evaluate the effect of adding N-(n-butyl) thiophosphoric triamide (NBPT) and dicyandiaminde (DCD) to urea fertilizer, on the physiology and growth of cotton (Gossypiumhirsutum L.) under normal and high temperatures. Treatments consisted of two day temperature regimes, 30°C and 38°C, and five nitrogen fertilization applications: unfertilized control, 125 kg ha^?1 of urea, 93 kg ha^?1 of urea, 93 kg ha^?1 urea + NBPT, and 93 kg ha^?1 urea + NBPT + DCD. The addition of NBPT to urea fertilizer had positive effects on leaf chlorophyll, leaf area, dry matter, nitrogen (N) uptake, and N use efficiency. The absence of a significant interaction effect indicated that N fertilization was not influenced by temperature. Deficiency of N significantly decreased leaf chlorophyll, increased glutathione reductase, decreased protein and increased leaf nitrate reductase. Physiological changes under high temperature included increased plant N uptake, glutamine synthetase, leaf chlorophyll, protein content, plant height and leaf area were due to high N uptake and utilization.     

Fate of 15N-Labeled Potassium Nitrate in Different Citrus-Cultivated Soils: Influence of Spring and Summer Application

The fate of ¹⁵N-labeled potassium nitrate (8.5% ¹⁵N excess) was determined in 3-year-old Valencia orange trees grown in 1-m³ containers filled with different textured soils (sandy and loamy). The trees were fertilized either in spring (24 March) or summer (24 July). Spring fertilized trees gave higher fruit yields in sandy than in loamy soils, which exceeded summer fertilized trees in both cases. Summer fertilized trees had greater leaf biomass than spring fertilized trees. Fibrous root weight was 1.9-fold higher in sandy than in loamy soil. At the end of the cycle, tree N recovery from spring application was 45.7% for sandy and 37.7% for loamy soil; from summer fertilization, N recovery was 58.9% and 51.5% for sandy and loamy soils, respectively. The ¹⁵N recovered in the inorganic soil fraction (0?C90?cm) was higher for loamy (1.3%) than for sandy soil (0.4%). Fertilizer N immobilized in the organic matter was lower in sandy (2.5%) than in loamy soil (6.0%). Potential nitrate leaching from fertilizer (¹⁵NO ₃ ^? ?CN in the 90?C110-cm soil layer plus ¹⁵NO ₃ ^? ?CN in drainage water) was 34.8% higher in sandy than in loamy soil. The low N levels in sandy soil resulted from both higher NO ₃ ^? ?CN leaching losses and higher N uptake of plants grown in the former. The great root mass and higher soil temperatures could account for raised plant N uptake in sandy soil and in summer, respectively.     

Effects of a nitrification inhibitor on efficiency of nitrogen utilization by wheat and millet

Abstract

Preliminary soil incubation studies established that the nitrification inhibitor, Dicyandiamide (DCD), could maintain the ratio of NH.‐N to NO₃‐N at predetermined levels. When one part DCD was mixed with 10 parts of the ammonium fertilizer prior to incorporation with the soil, nitrification was inhibited for at least six weeks. In a greenhouse experiment, wheat was grown to maturity and millet to the flowering stage in pots containing nitrate and ammonium fertilizers treated with DCD. Soil analyses during the plant growth period indicated that ammonium oxidation in soil was effectively inhibited. Plants of both species exposed to ammonium only with DCD produced lower yields than those exposed to a mixture of nitrate and ammonium nitrogen with DCD. Plants supplied with nitrate‐only gave somewhat lower yields than the mixtures. The nitrate‐only treatments resulted in the lowest accumulation of reduced nitrogen compounds in shoots of both species. Magnesium uptake by millet and calcium and magnesium uptake by wheat were reduced as the proportion of ammonium in soil was increased.     

Plant availability of magnesium and phosphorus from struvite with concurrent nitrification inhibitor application

Struvite (MgNH₄PO₄.6H₂O) and nitrification inhibitors are applied to soils to, respectively, provide nutrients and reduce nitrogen (N) loss. Given its low N composition (5.7%) relative to that of phosphorus (P, 12.6%) and magnesium (Mg, 9.9%), struvite could be added to soil concurrently with N fertilizers as a source of P and Mg. Nutrient release from struvite could be impacted if nitrification of its ammonium component is reduced by a nitrification inhibitor. Accordingly, a pot trial gauged whether struvite‐fertilized ryegrass had comparable Mg or P uptake and shoot yields with treatments receiving conventional Mg and P fertilizers. Struvite precipitated from milk industry wastewater, or conventional fertilizers, were added to a soil–sand mixture of low fertility. The inhibitor dicyandiamide (DCD) was added to assess its effect on P uptake by ryegrass. Relative to Epsom salt, struvite led to increased Mg uptake without significantly affecting shoot biomass, indicating luxury consumption. Regarding shoot yield and P uptake, struvite was as effective as triple super phosphate. DCD significantly reduced P uptake in the first harvest; the inhibited nitrification of the ammonium is surmised to have diminished struvite dissolution. In later harvests, DCD led to a trend (albeit not statistically significant) of increased biomass; this N‐rich (66% N) compound was probably biodegraded and utilized as an N source. The impact of DCD on P uptake in this experiment was short‐lived. Nevertheless, DCD degradation occurs less rapidly in field conditions, potentially affecting early P supply which is vital for optimum yield.     

Effect of dicyandiamide on the form and recovery of 15N‐labeled urea in the delayed flood soil system

Abstract

Dicyandiamide (DCD) is a nitrification inhibitor that has been proposed for use in drill‐seeded rice. Immobilization of fertilizer NH₄ ⁺‐N by soil microorganisms under aerobic conditions has been found to be significantly enhanced in the presence of a nitrification inhibitor. The objective of this laboratory study was to determine if DCD significantly delayed nitrification of urea‐derived N, and if this enhanced immobilization of the fertilizer N in the delayed‐flood soil system inherent to dry‐seeded rice culture. Nitrogen‐15‐labeled urea solution, with and without DCD (1: 9 w/w N basis), was applied to a Crowley silt loam (Typic Albaqualf) and the soil was incubated for 10 weeks in the laboratory. The soil was maintained under nonflooded conditions for the first four weeks and then a flood was applied and maintained for the remaining six weeks of incubation. The use of DCD significantly slowed the nitrification of the fertilizer N during the four weeks of nonflooded incubation to cause the (urea + DCD)‐amended soil to have a 2.5 times higher fertilizer‐derived exchangeable NH₄+‐N concentration by the end of the fourth week. However, the higher exchangeable NH₄+‐N concentration had no significant effect on the amount of fertilizer N immobilized during this period. Immobilization of the fertilizer N appeared to level off during the nonflood period about the second week after application. After flooding, immobilization of fertilizer N resumed and was much greater in the (urea + DCD)‐amended soil that had the much higher fertilizer‐derived exchangeable NH₄ ⁺‐N concentration. Immobilization of fertilizer N appeared to obtain a maximum in the urea‐amended soil (18%) about two weeks after flooding and for the (urea + DCD)‐amended soil (28%) about four weeks after flooding.     

The effect of dicyandiamide and neem cake on the nitrification of urea-derived ammonium under field conditions

Summary Dicyandiamide (DCD) and neem cake were evaluated for their efficiency in inhibiting nitrification of prilled urea-derived NH ₄ ⁺ –N in a wheat field. Prilled urea was blended with 10% and 20% DCD-N or 10% and 20% neem cake and incorporated into the soil just before the wheat was sown. Both DCD and neem cake partially inhibited nitrification of prilled urea-derived NH ₄ ⁺ ; DCD was better than neem cake. The nitrification-inhibiting effects of DCD lasted for 45 days, while that of neem cake lasted for only 30 days. Blending the prilled urea with DCD (20% on N basis) was most effective in inhibiting the nitrification of urea-derived NH ₄ ⁺ , both in terms of intensity and duration, and maintained substantially more NH ₄ ⁺ –N than the prilled urea alone and 20% neem-cake-blended urea for a period of 60 days.     

Ammonium fixation from urea as influenced by nitrapyrin

Abstract

During the period 1977–1979, NaNO₃, urea, and urea plus 2% (wt/wt) nitrapyrin (2‐chloro‐6‐(trimethyl)pyridine) were compared on a Matapeake silt loam (fine silty mixed mesic Typic Hapludult) . Nitrogen sources were injected as solutions into the water system at 224 kg N ha^‐1yr^‐1used for subsurface trickle irrigation of corn (Zea maysL.). Nitrogen was withheld in 1980 in order to assess residual N effects. Grain yields in 1980 for the NaNO₃, urea, and urea plus Nitrapyrin treatments were 5.10, 4.56 and 6.52 Mg ha^‐1, respectively. Corresponding ear leaf N concentrations were 17.7, 16.7 and 19.2 g kg^‐1. Significantly higher grain yield and leaf N concentrations associated with the use of nitrapyrin as a nitrification inhibitor indicated greater soil N reserves for this treatment. Non‐exchangeable (fixed) NH₄ ⁺, in soil cores taken in November 1981 averaged 54, 59 and 74 ug N g^‐1for the respective N regimes. The concentration of fixed NH₄ ⁺increased with sampling depth, averaging 54, 61 and 72 ug N g^‐1for the 0–5, 30–35, and 60–65 cm profile depths, respectively. This trend is ascribed to increasing quantities of micaceous and vermiculitic clay (<2 um) with increasing profile depth.     

Controlled‐release urea decreased ammonia volatilization and increased nitrogen use efficiency of cotton

Excessive nitrogen (N) fertilizer input leads to higher N loss via ammonia (NH₃) volatilization. Controlled‐release urea (CRU) was expected to reduce emission losses of N. An incubation and a plant growth experiment with Gossypium hirsutum L. were conducted with urea and CRU (a fertilizer mixture of polymer‐coating sulfur‐coated urea and polymer‐coated urea with N ratios of 5 : 5) under six levels of N fertilization rates, which were 0% (0 mg N kg⁻¹ soil), 50% (110 mg N kg⁻¹ soil), 75% (165 mg N kg⁻¹ soil), 100% (220 mg N kg⁻¹ soil), 125% (275 mg N kg⁻¹ soil), and 150% (330 mg N kg⁻¹ soil) of the recommended N fertilizer rate. For each type of N fertilizer, the NH₃ volatilization, cotton yield, and N uptake increased with the rate of N application, while N use efficiency reached a threshold and decreased when N application rates of urea and CRU exceeded 238.7 and 209.3 mg N kg⁻¹ soil, respectively. Ammonia volatilization was reduced by 65–105% with CRU in comparison to urea treatments. The N release characteristic of CRU corresponded well to the N requirements of cotton growth. Soil inorganic N contents, leaf SPAD values, and net photosynthetic rates were increased by CRU application, particularly from the full bloom stage to the initial boll‐opening stage. As a result, CRU treatments achieved significantly higher lint yield by 7–30%, and the N use efficiency of CRU treatments was increased by 25–124% relative to that of urea treatments. These results suggest that the application of CRU could be widely used for cotton production with higher N use efficiency and lower NH₃ volatilization.     

Aluminum tolerance,mineral nutrition,and growth of ‘Helleri’ holly in solution culture

‘Helleri’ holly (Ilex crenata Thunb. ‘Helleri') plants were grown in solution culture at aluminum (Al) concentrations of 0, 6, 12, 24, and 48 mg.L^‐1 for 116 days. Aluminum did not affect root or crown index, stem length growth, plant dry weight, or leaf area. Aluminum treatments significantly increased Al uptake and reduced nutrient uptake of magnesium (Mg), calcium (Ca), zinc (Zn), and copper (Cu) on some sampling dates. Iron (Fe) and manganese (Mn) uptake decreased on most sampling dates but increased on some with Al treatments. Potassium (K), phosphorus (P), and boron (B) uptake were significantly affected by Al, decreasing and increasing at different sampling dates. Although plants preferentially took up ammonium‐nitrogen (NH₄ ⁺‐N) in all treatments (including 0 Al controls), neither NH₄ ⁺‐N nor nitrate‐nitrogen (NO₃ ‐N) uptake were affected by Al. Tissue concentrations of P, K, B, Zn, and Al increased with Al treatment; whereas tissue Ca, Mg, and Cu concentrations decreased with increasing Al. Iron and Mn tissue concentrations exhibited increases and decreases in different tissues. Results indicated that ‘Helleri’ holly was tolerant of high concentrations of Al.     

Effect of nitrogen form during the flowering period on zucchini squash growth and nutrient element uptake

Zucchini squash (Cucurbita pepo L. cv. Green Magic) plants were grown hydroponically with nitrate (NO₃):ammonium (NH₄) ratio of 3:1 until the onset of flowering when the plants were assigned to four NO₃:NH₄ ratio (1:0, 1:1, 1:3, or 3:1) treatments. Changing the original nitrogen (N) form ratio significantly affected plant growth, fruit yield, nutrient element, and water uptake. Growth of plants was better when NO₃‐N (1:0) was the sole form of N than when NH₄‐N was part of the N treatment. Fruit yields for plants fertilized with 1:0 or 1:3 N‐form ratio were double those of plants grown continuously with 3:1 N ratio. The largest leaf area and plant water use were obtained with 1:0 N ratio treatment Total uptake of calcium (Ca), magnesium (Mg), and potassium (K) decreased with increasing NH₄‐N proportion in the nutrient solution which suggest NH₄‐N was competing with these cations for uptake. The results also demonstrated that growers may increase fruit yield by using a predominantly NO₃‐N source fertilizer through the vegetative growth stage and by shifting the NO₃:NH₄ ratio during the reproductive phase.     

Influences of ultra‐violet (UV)‐blue light radiation on the growth of cotton. I. Effect on iron nutrition and iron stress response

Cool white fluorescent (CWF) light reduces Fe³⁺ to Fe²⁺ while low pressure sodium (LPS) light does not. Cotton plants grown under CWF light are green, while those yrown under LPS light develop a chlorosis very similar to the chlorosis that develops when the plants are deficient in iron (Fe). It could be that CWF light (which has ultra violet) makes iron more available for plant use by maintaining more Fe²⁺ in the plant. Two of the factors commonly induced by Fe‐stress in dicotyledonous plants‐‐hydroyen ions and reductants released by the roots‐‐were measured as indicators of the Fe‐deficiency stress response mechanism in M8 cotton.

The plants were grown under LPS and CWF light in nutrient solutions containing either NO₃‐N or NH₄‐N as the source of nitrogen, and also in a fertilized alkaline soil. Leaf chlorophyll concentration varied significantly in plants grown under the two light sources as follows: CWF+Fe > LPS+Fe > CWF‐Fe ≥ LPS‐Fe. The leaf nitrate and root Fe concentrations were significantly greater and leaf Fe was generally lower in plants grown under LPS than CWF light. Hydrogen ions were extruded by Fe‐deficiency stressed roots grown under either LPS or CWF light, but “reductants”; were extruded only by the plants grown under CWF light. In tests demonstrating the ability of light to reduce Fe³⁺ to Fe²⁺ in solutions, enough ultra violet penetrated the chlorotic leaf of LPS yrown plants to reduce some Fe³⁺ in a beaker below, but no reduction was evident through a yreen CWF grown leaf.

The chlorosis that developed in these cotton plants appeared to be induced by a response to the source of liyht and not by the fertilizer added. It seems possible that ultra violet liyht could affect the reduction of Fe³⁺ to Fe²⁺ in leaves and thus control the availability of this iron to biological systems requiring iron in the plant.     

Elemental leaf content and deficiency symptoms in rabbiteye blueberries: 1. Nitrogen

Rabbiteye blueberries grown in sand culture were subjected to varying levels of N fertilization (0 ‐ 81 mg N/liter) applied in aqueous solution at the rate of 250 ml/plant daily. Essential elements other than N were kept constant. Shoot growth and leaf concentration of N, P, K, Mg, Ca, Mn, Fe, Cu, B, Zn, Co, and Al were determined. Shoot growth and percent leaf N increased with increased N levels. Shoot growth increased little at N fertilization levels of 0 ‐ 9 mg/ liter but increased rapidly at higher rates. N content in leaves followed a quadratic curve, with % N in leaves increasing more rapidly from 0 to 27 mg N/liter than from 27 to 81 mg N/liter fertilization levels. Leaf concentration of K, Ca, Mg, Mn, B, and Ca decreased linearly as N levels increased. Total content of all elements increased as N fertilization increased. Visual N deficiency became increasingly evident as % N content decreased below 1.4% N.

Nitrogen, the most utilized element in plants, is usually the first to become deficient in sandy soils low in nutrient content (1). Rabbiteye blueberries (Vaccinium ashei Reade) are often grown on acidic, sandy, upland coastal plains soils that are low in cation exchange capacity, organic matter content, and available nutrients. In these acidic soils, NH₄N is more available than in neutral soils (2). The NH₄N source appears to be more suitable for blueberry growth, resulting in greater nutrient uptake, plant growth, and % N of leaf tissue than did the NO₃N sources (5,6).

Nitrogen deficiency symptoms in rabbiteye blueberries are characterized by small, yellow and/or red leaves and stunted plants (3). Since young rabbiteye plants are very sensitive to fertilizer, similar chlorosis symptoms (yellowing or reddening of leaves) can be associated with over‐fertilization, possibly due to root damage (7). Cain (2) found that leaves from healthy container‐grown highbush (V. corymbosum L.) blueberry plants contained about 2% N and higher levels of K and Ca than field‐grown plants. Greenhouse and Field studies indicate that leaf N content in rabbiteye blueberries is usually lower, ranging from about 1.5 to 1.8 (3,7,8). Increased N fertilization decreased the nutrient uptake of other essential elements (Ca and Mg) in rabbiteye blueberries (6). In highbush, Popenoe (4) indicated that a depression of P and K might occur under conditions of high N levels.

This study was initiated to ascertain the effect of NH₄N fertilization levels on uptake patterns of essential elements and to determine the relationships of N fertilization, leaf N content, plant growth, and visible deficiency symptoms.     

Mitigation of alkaline stress by arbuscular mycorrhiza in zucchini plants grown under mineral and organic fertilization

A greenhouse experiment was carried out during the spring–summer 2009 to test the hypotheses that: (1) arbuscular‐mycorrhizal (AM) inoculation with a biofertilizer containing Glomus intraradices gives an advantage to overcome alkalinity problems, (2) mineral fertilization is more detrimental to AM development than organic fertilization on an equivalent nutrient basis. Arbuscular mycorrhizal (AM) and non‐AM of zucchini (Cucurbita pepo L.) plants were grown in sand culture with two pH levels in the nutrient solution (6.0 or 8.1) and two fertilization regimes (organic or mineral). The high‐pH nutrient solution had the same basic composition as the low‐pH solution, plus an additional 10 mM NaHCO₃ and 0.5 g L^–1 CaCO₃. Increasing the concentration of NaHCO₃ from 0 to 10 mM in the nutrient solution significantly decreased yield, plant growth, SPAD index, net assimilation of CO₂ (A_CO2), N, P, Ca, Mg, Fe, Mn, and Zn concentration in leaf tissue. The +AM plants under alkaline conditions had higher total, marketable yield and total biomass compared to –AM plants. The higher yield and biomass production in +AM plants seems to be related to the capacity of maintaining higher SPAD index, net A_CO2, and to a better nutritional status (high P, K, Fe, Mn, and Zn and low Na accumulation) in response to bicarbonate stress with respect to –AM plants. The percentage root colonization was significantly higher in organic‐fertilized (35.7%) than in mineral‐fertilized plants (11.7%). Even though the AM root colonization was higher in organic‐fertilized plants, the highest yield and biomass production were observed in mineral‐fertilized plants due to the better nutritional status (higher N, P, Ca, and Mg), higher leaf area, SPAD index, and A_CO2.     

Nitrogen effect on yield and kernel protein content of sweet corn grown on sandy soils

Abstract

Early spring application of N to Iowa sandy, leachable soils results in reduced sweet corn yields and kernel protein content. Normally, split N applications are used to coincide with crop N demand. Our objectives were to determine if nitrapyrin, a nitrification inhibitor, applied with urea would provide high yields and kernel protein levels when applied at planting.

Nitrogen rate increased yield, ear leaf N concentration, and kernel protein content in 1976 and 1978, with the optimum rate dependent on the year and soil N residual. Urea, with or without nitrapyrin, significantly enhanced yield 13%, early leaf N concentration 17%, and kernel protein content 9% as compared with Ca(NO₃)₂ for both years. High leaching loss of NO₃‐N occurred with the Ca(NO₃)₂ source as compared with urea alone. Kernel protein concentration correlated well with ear leaf N concentration (r = .74) and yield (r = .61). Ear leaf K content was not affected by N rate or source, but Ca(NO₃)₂ enhanced uptake of Ca and Mg as compared with the urea sources. Urea, with nitrapyrin, decreased leaf Mg content in 1978, but not in 1976, as compared with urea alone.     

Decomposition rate of dicyandiamide and nitrification inhibition

Abstract

Degradation of dicyandiamide (DCD) was assayed in laboratory studies at 8, 15, and 22 C in a Decatur silt loam and in a Norfolk loamy sand. Dicyandiamide was very short lived at 22 C, with half‐lives of 7.4 and 14.7 days in the Decatur and Norfolk soils, respectively. In the Norfolk soil at 8 C, half‐life increased to 52.2 days. In a nitrificaton study of both soils at 22 C, 80 mg (NH₄)₂SO₄‐N kg^‐1 of soil was applied with 20 mg DCD‐N kg^‐1 of soil and 100 mg kg^‐1 (NH₄)₂S0₄‐N was added with 5% nitrapyrin. Distinct lag phases preceded zero order nitrification with the inhibitor treatments. Lag periods were 2 and 2.6 times the half life of DCD in the degradation study for Decatur and Norfolk soils, respectively. Like most nitrification inhibitors, the effectiveness of DCD decreases with increasing temperature. In the Norfolk loamy sand, nitrification inhibition by DCD was equal to nitrapyrin for up to 42 days, but in Decatur silt loam, DCD was less potent to nitrapyrin as a nitrification inhibitor.     

Dicyandiamide increases the fertilizer N loss from an alkaline calcareous soil treated with <Superscript>15</Superscript>N-labelled urea under warm climate and under different crops

Using an alkaline calcareous soil, experiments were conducted to elucidate the effects of nitrification inhibitor dicyandiamide (DCD) on the fate of ¹⁵N-labelled urea applied to cotton, maize, and wheat under greenhouse conditions. Combined effects of DCD and two levels of wheat straw (applied to cotton) and of fertilizer application method (conventional broadcast vs. point injection in maize and wheat) on the recovery of the fertilizer N were also studied. High soil temperatures prevailed under cotton and maize, whereas the soil temperature was relatively moderate during the wheat growing season. The fertilizer N loss under cotton was lowest (44% of the applied) when urea was applied alone; the loss increased due to DCD (54%) or wheat straw (50–54%) and was highest (63–64%) when DCD and wheat straw were applied together. Under maize also, DCD increased the loss of the fertilizer N applied by the conventional method (51% without DCD vs. 66% with DCD) or by point injection (26% without DCD vs. 42% with DCD). With the conventional method under wheat, DCD had no effect on the fertilizer N loss (34–37% of the applied). The fertilizer N loss under wheat was least (16%) when urea solution was point-injected but increased (24–26%) due to DCD or/and when pH of the urea solution was reduced to 2. Besides, DCD significantly reduced the fertilizer N uptake and increased the fertilizer N immobilization in soil under cotton and maize. However, DCD applied in combination with a higher level of wheat straw significantly increased the cotton dry matter and N yields due to increased N availability from sources other than the fertilizer. The results suggested that the use of DCD may not be beneficial in alkaline calcareous soils and that point injection of urea solution without any amendment is more effective in conserving the fertilizer N as compared to the conventional broadcast method.     

Corn response to two fertilization rates under Sw Spain conditions

Abstract

Corn cv. PRISMA response (growth, plant composition, and yield) was studied in relation to two fertilizer treatments: the high rate used in irrigated fields in SW Spain (1000 kg/ha 15–15–15 fertilizer plus two applications of 400 kg urea (46%N)/ha); and the same reduced to one‐third. Plant height (～ 290 cm), specific leaf area (0.018 m²/g), ear weight (～210 g), kernel weight per ear (～185 g), and estimated yield (～16 Mg/ha) were similar with both treatments. Plant nutrient contents were similar in the leaf level, with both treatments, although the N content of stalk and kernel (at harvest) were higher (P<0.05) when the high fertilization dose was applied. DRIS indices presented N and S as the more balanced nutrients, and in general the P and Mg contents were comparatively low, and Ca and K comparatively high. Amounts of N and P removed by corn (above‐ground part) were higher than those fertilized at the lower rate. Removed K was considerably higher than the loaded amount, whichever rate of fertilization was considered. When fertilized with a comparatively low rate (for irrigated regimes in SW Spain), the natural reserves of the previously fertilized sandy loam soil used in the assay contributed to achieve a high yield with a high‐yielding corn crop.     

Yield of take‐all infested winter wheat as influenced by inhibiting nitrification with dicyandiamide

Abstract

The potential for using dicyandiamide (DCD) to enhance yield of take‐all‐infested winter wheat (Triticum aestivum L.) was evaluated in six field experiments on four acid soils (pH 5.7–6.2). Ammonium and NO₃ ^‐ concentrations and NH₄ ⁺: NO₃ ^‐ ratios in 0–10 and 10–20 cm soil depths were measured for ten weeks after spring topdressing 180 kg N/ha as urea with 0, 13, or 27 kg DCD/ha. Nitrification was strongly inhibited for 6 to 10 weeks by either 13 or 27 kg DCD/ha. Averaged over the ten‐week sampling period, NH₄ ⁺: N0₃ ^‐ ratios in the 0–10 cm depth of soil were 36: 1 for DCD‐treated plots as compared to 2: 1 for plots receiving only urea. Ratios in DCD‐treated plots were considerably wider than ratios associated with take‐all suppression (10: 1 to 3: 1) in earlier studies. Extractable NH₄ ⁺ + NO₃ ^‐ concentrations in soil were high in DCD‐treated plots after 30 to 40 days, suggested that DCD had reduced crop uptake of N because of the lower mobility of NH₄ ⁺ as compared to NO₃ ^‐. In four of the six studies, grain yields tended to be reduced by DCD. Results suggest that lower rates of DCD and/or application of some NO₃ ^‐ will be necessary if DCD is to be used as a tool for suppressing take‐all.