Applied phosphorus and potassium effects on yield of dallisgrass‐bermudagrass pastures 1

There are substantial areas of dallisgrass (Paspalum dilatatum Poir.)‐common bermudagrass (Cynodon dactylon (L). Pers.) summer‐type pastures in the Southeastern Central Plain, but little information is available on their response to P and K fertilization. The purpose of this study was to measure the response of dallisgrass‐common bermudagrass pastures to P and K fertilization with and with‐ out N. Phosphorus and K were applied to two soils in May each year for three years. Yield data were collected by clipping a swath through the length of the plots when the minimum forage height was approximately 30 cm. Responses to P and K applications were obtained when the soil test levels were low to very low, but not when they were medium as determined by the Mississippi Soil Test (MST). Forage P concentration of the control in the medium P and K soil was within the adequate range of 2.8 to 3.4 g/kg, but forage K concentration was below the critical range of 16 to 18 g/kg. Forage P and K concentrations of the controls in the low P and K soil were below critical levels. At both locations forage P and K concentrations were increased by P and K fertilization. Available soil P increased with rate of P application but soil extractable K was unaffected by K application. No yield response to P and K are likely at medium soil test levels (MST) even at high rates of N. There was no response to P and K application without N.     

Critical soil phosphorus of a low‐P loess‐derived soil as affected by storage temperature

Abstract

Overwintering soil temperature may influence crop response to phosphorus (P) and indices of P availability in the humid, temperate, transitional climate of Tennessee. The effects of P fertilization and soil incubation temperature on sorghumsudangrass (Sorghum bicolor x S. Sudanese) grown on a Typic Hapludalf was investigated in a greenhouse study. In order to determine the effect of temperature on P availability, soils were incubated prior to cropping, at a constant temperature of 6°C or an average diurnal temperature of 24 and 36°C. Reagent grade Ca(H₂PO₄)₂.H₂O was used as the fertilizer source and applied at rates of 0, 10, 20, and 30 mg P kg^‐1 for the first test and 0, 20, 40, 60, and 80 mg P kg_‐ ¹ for the second test. Critical P concentration in the shoots for optimum yield was found to be 1.3 mg g‐¹, corresponding to soil solution and labile P concentrations of 5.5 μmol L^‐1 and 167 μg g^‐1, respectively. Optimum yield occurred for applications of >65 mg P kg^‐1 and was unaffected by soil incubation temperature. Applied P rates affected extractable P by five chemical extractants (Bray I, Bray II, Mehlich I, Mehlich III, and Mississippi), but soil incubation temperature had no affect. The extractants, however, were poorly correlated to plant P uptake and no one extractant appeared preferable to the others as an indicator of P availability.     

Stimulation of N2‐fixation in chickpea by gamma irradiation as affected by different levels of ammonium sulfate fertilizer

Abstract

A pot experiment was conducted under natural climatic conditions to study the effect of low doses of gamma irradiation (0, 5, 10, and 20 Gy) on the performance of winter chickpea (Cicer arietinum L.) in the presence of increased supply of ¹⁵N labeled ammonium sulfate (0, 20, 50, and 100 kg N ha^‐1). Presowing seed irradiation produced a significant increase in dry matter production (up to 3 6%) and total nitrogen yield (up to 45%). The stimulative effect of irradiation was more pronounced with the application of NH₄ ⁺‐N fertilizer. Seed irradiation increased the amount of N₂‐fixation by 8–61% depending on the dose and level of NH₄ ⁺‐N fertilizer rate. A 10 Gy was found to be the optimal irradiation dose for enhancing N₂‐fixation. High levels of NH₄ ⁺‐N decreased the percentage and the amount of N₂‐fixation, but did not affect nodule formation. However, the presowing 10 Gy irradiation dose reduced the negative effect of ammonia‐N fertilizer on N₂‐fixation. Therefore, we recommend irradiating chickpea seeds with a 10 Gy dose before planting in soil containing high levels of mineral nitrogen to reduce its negative effect on N₂‐fixation.     

Rice yield and water use as affected by soil management practices

A field experiment was conducted at the Shenyang Experimental Station of Ecology, Chinese Academy of Sciences,to study the effects of soil management practices on water use and rice (Oryza sativa L.) yield in an axtuic brown soil during 2001 and 2002. A completely random experimental design with three replications was employed, having four soil management practices as treatments, namely: an undisturbed plow layer (CK), a thin plastic film (TN), a thick plastic film (TI) and subsoil compacting (CP). Results indicated no significant differences among all treatments for rice biomass and grain yields. Also, water consumption was about the same for treatments TN and CK, however the treatments TI and CP were much lower with more than 45% and 40% of the irrigation water in the treatments TI and CP, respectively,saved each year compared to CK. Therefore, water use efficiency was higher in the treatments TI and CP. These results will provide a scientific basis for the water-saving rice cultivation.     

Availability of phosphorus in a Brazilian Oxisol cultivated with eucalyptus after nine years as influenced by phosphorus‐fertilizer source,rate, and placement

Abstract

This work evaluated the effect of different placement and rates of two phosphorus (P) fertilizers on P‐availability by three methods of extraction, nine years after application to a Brazilian Oxisol cultivated with Eucalyptus camaldulensis. The treatments were applied to 24x18 m plots and 96 seedlings of E. camaldulensis were planted (3.0x1.5 m) in each plot. Single superphosphate (SSP) and rock phosphate (RP) were tested in three rates (100, 200, and 400 kg ha^‐1 of P₂O₅). Each fertilizer was either (1) surface‐applied in bands (0.6 m either side of the rows of trees) and incorporated before planting or (2) incorporated into furrows (0.2 m deep in the tree rows) before planting. As additional treatments, the combination of RP (96 kg ha^‐1 of P₂O₅ applied in broadcast, or bands, or in furrows) + SSP (54 kg ha^‐1 of P₂O₅ localized in the planting hole before planting) were tested. Twelve soil subsamples from two layers (0–15 and 25–40 cm) were taken from each plot (from the planting rows or between the planting rows) and were analyzed for pH in water (1:2.5), available P by Mehlich‐1, Bray‐1 and anionic resin, exchangeable Ca, and Al by 1 mol L^‐1 Kcl. For both methods of fertilizers placement, the highest values of available P were observed in the surface soil and in the planting row, and were strongly related to fertilizer rate. Samples taken between the planting rows did not exhibit treatment effects on available P. The higher values of available P obtained with Mehlich‐1 and the lower eucalyptus plant uptake efficiency of fertilizer‐P from banded RP confirms the fact that this extractant can overestimate the availability of P in soils receiving RP. The use of anion exchange resin in this situation to estimate available P is supported. The results obtained with the localized application of RP indicate root system activity (P and Ca uptake and acidification of rhizosphere) as a factor in increasing fertilizer dissolution rates.     

Dry matter yield and n recovery from bromegrass in south‐central alberta as affected by time of application of urea and ammonium nitrate

Abstract

Field experiments were conducted for periods of 14 or 15 years at four sites on Thin Black Chernozemic soils in south‐central Alberta to determine the effect of source and time of N application on dry matter yield (DMY), protein yield (PY), protein concentration, N use efficiency and recovery of N applied to bromegrass (Bromus inermis Leyss.) grown for hay. Two sources of N (urea and ammonium nitrate ‐ A.N.) were applied at four times (early fall, late fall, early spring and late spring) at a rate of 112 kg N ha^‐1. Urea was generally less effective in increasing DMY, PY, protein concentration, N use efficiency and % N recovery than A.N. The average, DMY, PY, protein concentration, N use efficiency and % N recovery with A.N. were 4.38 t ha^‐1, 445 kg ha^‐1, 104 g kg^‐1, 21.2 kg DM kg^‐1 N ha^‐1 and 40.2%, respectively. In the same order, the values with urea were 3.90 t ha^‐1, 376 kg ha^‐1, 99 g kg^‐1, 16.9 kg DM kg^‐1 N ha^‐1 and 30.2%, respectively. The DMY was greatest with early spring application for A.N., while the protein concentration, PY and % N recovery were greatest with the late fall application for both urea and A.N. The increase in DMY or recovery of applied N with urea as a percentage of the increase with A.N., was greatest with application in late spring and least with application in early fall. In conclusion, urea was less effective than A.N. as a forage fertilizer and early spring application was most effective for increasing DMY.     

Topsoil and subsoil potassium as affected by long‐term potassium fertilization of corn‐soybean rotations

Abstract

Long‐term potassium (K) fertilization practices are likely to affect the K content of soils. This study assessed the effect of long‐term K fertilization strategies for corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotations on extractable K in the soil profile of a major Iowa soil type at two locations. The soil type was a Webster fine‐loamy, mixed, mesic, Typic Haplaquoll at both sites. Soil samples were collected from the 0–15, 15–30, 30–60, and 60–90 cm depths after 17 years (Site 1) or 19 years (Site 2) of K fertilization with combinations of two initial rates and four annual rates. The initial rates were 0 and 1,344 or 1,120 kg K ha^‐1 at Site 1 and 2, respectively, and the annual rates ranged from 0 to 100 kg K ha^‐1. Samples were analyzed for ammonium acetate‐extractable K (STK) and nitric acid (HNO₃)‐extractable nonexchangeable K (HNO₃‐K). Concentrations of STK and HNO₃‐K in the top 0–15 cm soil layer at the two sites were higher for the high initial K rates and were linearly related with the annual K rate. Results for the subsoil layers varied between sites and extractants. At Site 1, annual rates of 30 kg K ha^‐1 or higher resulted in a relative accumulation of HNO₃‐K in the 15–30 cm layer. At Site 2, these rates resulted in relative accumulations of STK in the 30–60 cm layer and of HNO₃‐K in the 60–90 cm layer, but with relative depletions of STK in the 15–30 and 60–90 cm layers. Thus, use of one extractant may not always be sufficient to evaluate cropping and fertilization effects on subsoil K. Long‐term K fertilization of corn and soybean rotations affected extractable K of both the topsoil and subsoil. The effects on subsoil K, however, were smaller compared with effects on the topsoil and varied markedly between sites, subsoil layers, and extractants.     

Soil organic phosphorus and microbial community composition as affected by 26 years of different management strategies

Agricultural management can affect soil organic matter chemistry and microbial community structure, but the relationship between the two is not well understood. We investigated the effect of crop rotation, tillage and stubble management on forms of soil phosphorus (P) as determined by solution ³¹P nuclear magnetic resonance spectroscopy and microbial community composition using fatty acid methyl ester analysis in a long-term field experiment (26 years) on a Chromic Luvisol in New South Wales, Australia. An increase in soil organic carbon, nitrogen and phosphorus compared to the beginning of the experiment was found in a rotation of wheat and subterranean clover with direct drill and mulching, while stubble burning in wheat–lupin and wheat–wheat rotations led to soil organic matter losses. Microbial biomass was highest in the treatment with maximum organic matter contents. The same soil P forms were detected in all samples, but in different amounts. Changes in organic P occurred mainly in the monoester region, with an increase or decrease in peaks that were present also in the sample taken before the beginning of the experiment in 1979. The microbial community composition differed between the five treatments and was affected primarily by crop rotations and to a lesser degree by tillage. A linkage between soil P forms and signature fatty acids was tentatively established, but needs to be verified in further studies.     

Relationship between soil‐test P and K and yield response of runner peanuts to fertilizer

Abstract

Direct fertilization of peanuts (Arachis hypogaeaL.) with P and K has generally shown few yield responses, resulting in only limited information concerning critical soil‐test levels of P and K. The purpose of the experiments in this report was to determine the critical soil‐test levels of P and K for runner peanuts using the double‐acid extraction procedure. Fertilizer experiments were conducted on farmers’ fields from 1973 to 1986. Site selection was based on soil test data that indicated “medium”; or “low”; levels of available P or K but “high”; in Ca and Mg. Phosphorus and potassium were applied together at all sites at rates of 20 and 74 kg/ha, respectively, as concentrated superphosphate and potassium chloride.

There were yield increases to fertilizer in 6 of the 39 experiments. Soil‐test P for these six ranged between 4 and 53 kg/ha; soil‐test K ranged between 10 and 31 kg/ha. Delineating the yield effect into their P and K components with the aid of multiple regressions of yield on soil test values showed that yield increases were due to the K component of the fertilizer. The critical soil‐test K value was calculated to be 37 kg/ha. Sound mature kernels (SMK) were generally unaffected by fertilizer.     

No‐tillage corn response to placement of fertilizer nitrogen,phosphorus, and potassium

Abstract

Fertilizer placement for corn (Zea mays L.) has been a major concern for no‐tillage production systems. This 3‐yr study (1994 to 1996) evaluated fertilizer phosphorus (P) or potassium (K) rates and placement for no‐tillage corn on farmers’ fields. There were two sites for each experiment involving fertilizer P or K. Treatments consisted ofthe following fertilizer rates: 0,19,and 39 kg P ha^‐1 or 0, 51, and 102 kg K ha^‐I. The fertilizer was broadcast or added as a subsurface band 5 cm beside and 5 cm below the seed at planting. Early plant growth, nutrient concentrations, and grain yields were measured. At the initiation of the study, soil test levels for P and K at the 0–1 5 cm depths ranged from optimum (medium) to very high across sites. Effects of added fertilizer and placement on early plant growth and nutrient concentrations were inconsistent. Added fertilizer had a significant effect on grain yields in two of twelve site‐years. Therefore, on no‐tillage soils with high fertility, nutrient addition, and placement affected early plant growth and nutrient utilization, but had limited effect on grain yield. Consequently, crop responses to the additions of single element P or K fertilizers under no‐tillage practices and high testing soils may not result in grain yield advantages for corn producers in the Northern cornbelt regardless of placement method.     

Iron chlorosis in macadamia as affected by phosphate‐iron interactions 1

Iron (Fe) chlorosis induced by heavy phosphate (P) fertilizations is a serious problem for macadamia (Macadamia integrifolia) in Hawaii. To address this problem, a study was conducted to quantify the effects of P‐Fe interaction on macadamia leaf composition and chlorosis. The soil used was a limed Oxisol (Tropeptic Eutrustox, Wahiawa Series), pH 5.5. Phosphate was added as treble superphosphate at 0, 150 and 500 mg P/kg. The 150 mg P/kg rate was designed to yield approximately 0.04 mg P/L in the soil solution, a level considered adequate for macadamia growth. The 500 mg P/kg rate was intended to produce approximately 0.2 mg P/L, a level required by many horticultural crops but considered excessive for macadamia. Iron was added as Fe‐DTPA at 0, 5 and 10 mg Fe/kg soil, and factorially imposed on the P treatments. Color Index, a numerical rating based on hue, value and chroma from a Munsell Color Chart for Plant Tissues, was correlated with leaf chlorophyll concentration and used as an indicator of chlorosis.

Phosphate concentrations in leaves increased with increasing P application rates as expected, but decreased remarkably with increasing Fe rates (at a constant P rate). Plant Fe unexpectedly remained unchanged with increasing Fe rates but decreased with increasing P rates. The results suggest that (1) soil‐solution Fe was not a limiting factor to macadamia growth as is often incorrectly assumed for high P‐fertilized soils, (2) Fe uptake was restricted not because soil‐solution Fe was low but because plant P was excessively high, and (3) Fe translocation from roots to leaves may have been hampered by high P in the plants. Consequently, Fe chlorosis was intensified primarily by P fertilization (actually, by high plant P concentrations) and secondarily by P‐Fe interactions. Chlorosis, as measured by Color Index, can be diagnosed by a leaf Fe/P ratio < 0.06, and predicted by a soil‐solution ³√Fe/P ratio < 15.     

Relationship among nitrogen and phosphorus contents of vegetative parts and agronomic traits of normal‐ and high‐protein wheats 1

Nitrogen and phosphorus fertilizers were applied at different levels to three hard winter wheat cultivars ranging in grain protein potential to elucidate their interaction and relationship to yield components. Plant N content was higher in the high‐protein cultivar than in the normal‐protein cultivars at jointing two years and at anthesis one year. Plant P content was higher in the semidwarf cultivars than in the tall cultivar and was unrelated to protein potential. All cultivars contained similar plant N and P levels at maturity. Nitrogen fertilization increased plant N content and decreased plant P content at all stages, whereas P fertilization usually increased plant P content but did not affect plant N content. Grain protein was correlated positively with plant N content at all stages and with plant P content at maturity. Grain yield was correlated positively with plant N content at anthesis but correlated negatively with plant P content at maturity. We concluded that high plant N content at anthesis is necessary for high grain yield and protein content regardless of the cultivars¹ inherent protein potential and that plant P nutrition is more critical when N nutrition is altered by fertilization or by genetics.     

Effect of levels of take‐all and phosphorus fertiliser on the dry matter and grain yield of wheat

In a field experiment with wheat (Triticum aestivum L.), the effect of the percentage severity of take‐all on the production of dried tops and grain and the kernel weight (mg/seed) was measured when different amounts of phosphorus (P) fertiliser were applied. The soil was severely P deficient. The amounts of P fertitiser varied from nil P (deficient) to 40 kg P/ha (adequate) applied annually. The levels of Gaeumannomyces graminis tritici (Ggt) were generated by four cropping sequences. The levels of percent severity of Ggt on plant roots ranged from low (<10% of wheat plant roots infected) to high (70% of roots infected by Ggt). Yield of dried tops, grain, and kernal weight, all increased as the level of P applied increased, but the amount of Ggt infection decreased. No grain was produced where no P was applied. The percentage increase in yield due to declines in the severity of take‐all was greater as the level of P applied increased. Increasing levels of P fertiliser help control the severity of Ggt (%) only where the initial level of Ggt with nil P fertiliser are moderate to low. Where the levels of Ggt severity are >65% the effectiveness of P in reducing the levels of Ggt severity rapidly declined. The percentage severity of Ggt affected the efficiency of plants to use P fertilisers. For each cropping sequence, a Mitscherlich function described the grain yield response to P fertiliser. The maximum grain yield (A coefficient) and the curvature coefficient (C) both declined with increases in the level of Ggt severity (%). For example, the C was significantly reduced from 0.134±0.03 for the least Ggt severity (%) to 0.00446±0.001 where Ggt was not controlled. The kernal weight (mg/seed) was increased by P application and decreased by Ggt infection.     

Seasonal development of biomass yield in grass–legume mixtures on different soils and development of above- and belowground organs of Medicago sativa

Grass–legume mixtures are suitable for crop rotations under organic farming. Little attention has been paid to seasonal development of mixtures with alfalfa under field conditions. We investigated the effects of site and cut on herbage and belowground biomass yields of grass–legume mixture and on above- and belowground traits of Medicago sativa. Six sites in southern Germany were monitored during 2011. Dry matter herbage yield ranged from 9 to 16 t ha^?1. The total herbage yield of three cuts per year decreased from 45% to 36% and 19%. The belowground biomass in the upper 30 cm soil layer ranged from 1.7 to 3.8 t ha^?1.There was no seasonal trend. Diameter of the root neck and maximum order of branching of alfalfa increased during the season. The number of nodules per plant decreased from 9.5–17.0 in May to 7.5–13.0 in August. By the last cut, roots with larger diameter created smaller nodules. More branched roots created more nodules independent of their shape. Thinner roots have more active nodules. Plant height, number of stems and inflorescences per plant were higher in July and August than in May. In conclusion, a holistic analysis including above- and belowground traits should be used for the evaluation of fodder crops.     

Influence of split‐applied nitrogen on grain yield and protein content in ten grain sorghum culti‐vars 1

More information on the response of newly developed or introduced grain sorghum cultivare to split‐applied nitrogen (N) in semi‐arid rainfed agriculture is needed. Therefore, the influence of four split‐applied N schedules (100/0, 66/34, 50/50, and 34/66) on six American (SC 283, SC 274, SC 669, B 66181, SC 33, and RTam 428), and four West African (CSm 63, 1S 6704c, 1S 7173c, and 1S 7419c) grain sorghum cultivars was evaluated. The split‐applied N significantly increased grain yield and percent protein in grain sorghum over a one‐time application of N. The increase in yield and protein content varied among varieties and schedules of N application. Varieties SC 574, RTam 428, and Csm 63 at split‐applied schedules of 66/34, 50/50, and 34/66, respectively, gave the highest yield over one‐time application of N. Similar differences in percent protein in grain among cultivars due to split‐applied N were observed.     

Adsorption‐desorption of zinc in mollisols and their relationship with uptake of fertilizer‐applied zinc by rice

Abstract

Zinc (Zn) adsorption in mollisols conformed to the linear form of Freundlich equation. The log K values were positively correlated with silt, clay, and carbonate contents and soil pH, but negatively correlated with sand content. Sequential desorption of adsorbed Zn in 0.05M Ca(NO₃)₂, 0.1M Mg(NO₃)₂, 0.005M DTPA, and 0.1M HCl revealed that weakly and specifically bound fractions of added Zn, which could easily equilibrate with soil solution, were low and decreased with silt and carbonate contents and soil pH. Weakly bound fraction increased with sand content. Strongly bound and complexed fraction of applied Zn was the maximum and increased with clay, soil organic carbon and carbonate contents and specific surface area, but decreased with sand content. The mineral bound fraction of applied Zn was intermediate and increased with silt, clay and carbonate contents, and soil pH and specific surface area. Zinc uptake due to added Zn fertilizer by rice crop (Y) negatively correlated with log K, but positively related to Zn content in the equilibrium soil extract and Zn desorbed in 0.05M Ca(NO₃)₂. Both log K and l/n values together explained 59.5% of the total variation in Y, while Zn content in the equilibrium soil extract, Zn desorbed in 0.05M Ca(NO₃)₂, 0.005M DTPA and 0.1M HCl collectively accounted 79.6% of the total variation in Y.     

Effect of rock phosphate and superphosphate on crop yield and soil phosphorus test in long‐term fertility plots

Abstract

A long‐term (1968–1987) field study using corn‐soybean in rotation was conducted to compare the effect of rock phosphate (RP) and superphosphate (SP) at two lime levels on crop yield, soil available phosphorus (P) as Bray P‐1 (0.025M HCl + 0.03M NH₄F) and Bray P‐2 (0.1M HCl + 0.03M NH₄F) tests, and on the relationship between crop yield and available P tests. Treatments included a control, application of RP and SP ranging from 12 to 96 kg P₂O₅ ha^‐1 yr^‐1, and combinations of RP with SP or sulphur at various rates. The RP was applied once in 1968 at 8 times the annual rate while SP was applied annually until 1985. Corn and soybean yields increased with P application, more with SP than with RP. Bray P‐l and Bray P‐2 increased linearly with the amount of P applied as SP or RP. A significant correlation (r > 0.64) was found between corn yield and Bray P‐2 at low lime level with both P sources. In contrast, a poor correlation (r < 0.50) was found between soybean yield and soil P tests. Both RP and SP were effective sources of P fertilizers for corn on soils treated with a small amount of lime compared with a large amount of lime. Under low lime the Bray P‐2 accounted for 41% and 66% variability in com yield with applied RP and SP, respectively. On the other hand, Bray P‐1 was only of value when SP was the source of P.     

The effect of subsurface aluminium on the growth and uptake of surface‐applied phosphorus by wheat seedlings 1

Seedlings of four cultivars of wheat (Triticum aestivum L.) differing in tolerance to aluminium (Al) were grown for 14 to 20 days using a split‐root sand/solution culture technique. Each culture tube was divided horizontally into two compartments by a root‐permeable paraffin wax barrier, so that phosphorus (P) and aluminium (Al) supply could be varied in the upper 0–80 mm (surface) and lower 80–180 mm (subsurface) compartments, respectively.

Root growth into the subsurface zone was enhanced by increased P supply to surface roots, but only in the absence of subsurface Al. Where subsurface Al was present, increased P supply to surface roots had no effect on the penetration of roots into the subsurface zone. Tolerance to Al in the cultivars used was therefore not related to the ability to translocate P to sites of Al injury.     

Time of availability influences mixed‐nitrogen‐induced increases in growth and yield of wheat 1

Previous studies have indicated that under hydroponic conditions, spring wheat (Triticum aestivum) plants produce higher grain yields, more tillers, and increased dry matter when continuously supplied with mixtures of NO₃ and NH₄ than when supplied with only NO₃. The objective of this study was to determine if mixed N needs to be available before or after flowering, or continuously, in order to elicit increases in growth and yield of wheat. During vegetative development, plants of the cultivar ‘Marshal’ were grown in one of two nutrient solutions containing either a 100/0 or 50/50 mixture of NO₃ to NH₄ and, after flowering, half the plants were switched to the other solution. At physiological maturity, plants were harvested, separated into leaves, stems, roots, and grain and the dry matter and N concentration of each part determined. Yield components and the number of productive tillers were also determined. Availability of mixed N at either growth stage increased grain yield over plants receiving continuous NO₃, but the increase was twice as large when the mixture was present during vegetative growth. When the N mixture was available only during vegetative growth the yield increase was similar to that obtained with continuous mixed N. The yield increases obtained with mixed N were the result of enhanced tillering and the production of more total biomass. Although plants receiving a mixed N treatment accumulated more total N than those grown solely with NO₃, the greatest increase occurred when mixed N was available during vegetative growth. Because availability of mixed N after flowering increased the N concentration over all NO₃ and pre‐flowering mixed N plants, it appears that the additional N accumulation from mixed N needs to be coupled with tiller development in order to enhance grain yields. These results confirm that mixed N nutrition increases yield of wheat and indicate that the most critical growth stage to supply the N mixture to the plant is during vegetative growth.     

Methane and nitrous oxide emissions as affected by organic–inorganic mixed fertilizer from a rice paddy in southeast China

Purpose

The effects of commercial compost fertilizer application on trace gas emissions are not well understood due to a lack of field experiments. The objective of this study was to evaluate the emissions of methane (CH₄) and nitrous oxide (N₂O) along with grain yield from a rice paddy as affected by different organic–inorganic mixed fertilizer (OIMF) treatments.

Materials and methods

A field experiment was initiated in 2006 with chemical compound fertilizer (CF) and three OIMF amendments including pig manure compost (PMC), Chinese medicine residue compost (CMC), and rapeseed cake compost (RCC), from a rice paddy in southeast China. The emissions of CH₄ and N₂O were simultaneously measured using the static opaque chamber method over the entire rice growing season in 2011. Soil biotic parameters were measured in soil collected after the rice was harvested in 2011.

Results and discussion

Relative to the control, the OIMF treatments significantly increased CH₄ emissions by 56–99 %, mainly due to exogenous organic substrate input, whereas no difference was observed in the CF treatment. The N₂O emissions were stimulated substantially by an average of 40 % due to nitrogen fertilization compared with the control. Consecutive OIMF application tended to increase the grain yield, making it marginally higher than that of the CF treatment (7 %, P?=?0.06). Compared with the control, the CF treatment slightly decreased the global warming potential and greenhouse gas (GHG) intensity, while they were remarkably increased in the OIMF treatments. Over the 5-year period of 2006–2011, the annual soil carbon sequestration rate was estimated to be 1.19 t C ha^?1 year^?1 for the control and 1.73–1.98 t C ha^?1 year^?1 for the fertilized treatments.

Conclusions

Our results suggest that despite the beneficial effects of increasing both grain yield and soil organic matter, OIMF application such as PMC, CMC, and RCC may be responsible for increased global warming due mainly to the stimulated CH₄ emissions. This effect should be thus taken into account when balancing agricultural production and GHG mitigation.