Effect of tebuthiuron on soil N mineralization and nitrification

Abstract

Herbicides have potential for economical and efficient site preparation following timber harvest. The effects of tebuthiu‐ron, one of the herbicides approved for this use, on soil nitrogen (N) mineralization and nitrification were determined in laboratory incubations. Tebuthiuron was added at rates from 0 to 1000 μg g^‐1 to three soils. There was no effect of tebuthiuron additions of less than 1 μg g^‐1 on soil N mineralization and nitrification. Tebuthiuron reduced nitrification in all soils at 1000 μg g^‐1 and in two of the soils at 100 μg g^‐1 . All soils had increased net mineralization with tebuthiuron added at 100 and 1000 μg g^‐1. The addition of 50 μg NH⁺ ₄‐N and 1000 μg tebuthiuron g^‐1 resulted in increased net mineralization in the three soils. Nitrification was affected differently in each of the three soils by the addition of both NH⁺ ₄‐N and tebuthiuron. The added NH⁺ ₄‐N either removed the inhibition of nitrification by the herbicide or had no effect on the inhibition in two of the soils. In the third soil, nitrification was reduced by the addition of NH⁺ ₄‐N.

The presence of NO^‐ ₃‐N in these acid soils and the effects of added NH⁺ ₄‐N on NO^‐ ₃‐N production suggest that heterotrophic nitrification occurs in at least two of the soils. The findings of this study indicate that any effects of tebuthiuron on N mineralization and nitrification at the currently recommended application rates are likely to be transient and localized.     

The diagnosis of nitrogen deficiency in wheat by means of a critical nitrate concentration in stem bases

Abstract

Stem bases from wheat plants in a glasshouse pot experiment conducted under varying nitrogen and two water regimes, were analysed for nitrate (NO₃) concentration. The concentration of NO₃ at three stages of growth i.e. tillering, jointing and anthesis were related both to rates of applied nitrogen and to shoot dry matter yield at time of sampling. Plotted against rate of increasing nitrogen application, the response curve of NO₃ concentration in wheat stem bases was sigmoidal. The level of nitrogen application at which NO₃ began to accumulate in the plants was the supply at which plants reached maximum dry matter yield. The concentration of NO₃ at which plant yield was 90% of maximum dry matter was taken as the critical level. This concentration was around 1000 ppm NO₃‐N at all stages. Compared with plants supplied with unlimited water, plants under moderate water stress accumulated relatively more NO₃ but had a similar critical NO₃ concentration.

Maximum grain yield was obtained from plants which stayed above the critical level throughout the growing season.     

Use of a chlorophyll meter to evaluate the nitrogen status of dryland winter wheat

Abstract

Chlorophyll meter leaf readings were compared to grain yield, leaf N concentration and soil NH₄‐N plus NO₃‐N levels from N rate studies for dryland winter wheat Soil N tests and wheat leaf N concentrations have been taken in the spring at the late tillering stage (Feekes 5) to document a crop N deficiency and to make fertilizer N recommendations. The chlorophyll meter offers another possible technique to estimate crop N status and determine the need for additional N fertilizer. Results with the chlorophyll meter indicate a positive association between chlorophyll meter readings and grain yield, leaf N concentration and soil NH₄‐N plus NO₃‐N. Additional tests are needed to evaluate other factors such as differences among locations, cultivars, soil moisture and profile N status.     

Selenium Concentration in Spring Wheat and Leaching Water as Influenced by Application Times of Selenium and Nitrogen

ABSTRACT

Selenium (Se) deficiency in Scandinavian soils is a common problem, and crops generally contain inadequate amounts to meet human need. This study shows a relationship of the Se concentration in spring wheat (Triticum aestivum L., c.v. ‘Helena’) and leaching water with timing of nitrogen (N) [as ammonium nitrate (NH₄NO₃)] and Se [as sodium selenate (Na₂SeO₄)] application. Ammonium-nitrate was applied by two methods (i) whole amount at sowing and (ii) in split application as 75% at sowing and 25% at stem elongation. Selenate was applied at cereal growth stages after sowing, e.g., tillering, stem elongation, head emergence, and milking. Split N application in comparison to one N application increased the grain protein content from 12.1 to 13.7 mg g^{? 1}, and grain Se was increased from 0.8 to 1.1 mg kg^{? 1} when Se was applied at stem elongation and from 0.6 to 0.9 mg kg^{? 1} when applied at heading. The highest Se concentration in plant was achieved with the split N application and Se application at stem elongation or heading. Selenium leaching losses increased with increasing selenium concentration in the wheat grains. No differences in Se leaching losses were obtained with split N application. Applying selenate and ammonium-nitrate together after tillering increased the grain Se concentration, but did not affect the potential leaching of Se, and thus could be considered as an appropriate time of application of these elements.     

Nutrient solution nitrogen form and barley yellow dwarf virus disease tolerance in oat and wheat

Abstract

The form of nutrient solution nitrogen (either NH₄‐N or NO₃‐N or mixtures of the two) provided to plants influences the severity of many crop diseases. This greenhouse study was conducted to determine how growth, grain yield, and yield components of oat (Avena sativa L.) and wheat (Triticum aestivum L.) plants given nutrient solutions containing different ratios of NO₃‐N to NH₄‐N would react to barley yellow dwarf virus (BYDV) infection. Fifteen‐day‐old seedlings (2nd leaf stage) were either infected with BYDV (PAV strain) or left uninfected. Nutrient solution treatments (started 19 d after germination) provided three ratios of NO₃‐N to NH₄‐N (100% NO₃, 50:50 NH₄:NO₃, or 100% NH₄) for a 30‐d period, after which plant height and tillers plant^?1 were measured. Oat and wheat plants given NH₄ had fewer tillers than plants given the other nutrient solution treatments. BYDV‐infected oat and wheat plants were shorter than uninfected plants. All pots then received NO₃ nutrient solution until plant maturity, after which days to anthesis, primary tiller height, grain yield and yield components were measured. In the NH₄ nutrient solution treatments, BYDV infection significantly reduced individual kernel weight in oat and primary tiller height in wheat. These same measures were not significantly affected by BYDV infection in the NO₃ or NH₄NO₃ nutrient solution treatments. There were no other significant nutrient solution by BYDV infection interactions for any other dependent variable measured. Nutrient solution treatments had no significant effect on grain yield, but BYDV infection reduced grain yield by 45% in oat and 46% in wheat. In conclusion, nutrient solution N form interacted with BYDV infection to alter disease tolerance in oat (kernel weight) and wheat (primary tiller height), but these alterations had no effect in ameliorating grain yield loss caused by BYDV disease.     

Correlation of soil test nitrogen with potato yields

Abstract

Yield response of Idaho Russet Burbank potatoes to nitrogen fertilizer was related to soil test for inorganic N (NO₃ ^‐ and NH₄ ⁺) in a total of 27 field experiments over a 3‐year period using polynomial correlation and regression analysis. Nitrate plus ammonium nitrogen content in the surface foot of soil was found to be useful in predicting yield response of potatoes to applied nitrogen.

Correlations between yield and extractable N were considerably better when the data from each cropping system were analyzed separately than when all locations were analyzed as one group. Additional improvement was obtained by including extractable ammonium nitrogen and nitrogen in the second foot of soil respectively. The best correlation with yield was found using (NO₃ ^‐ + NH₄ ⁺)‐N in the surface foot following grain and the top two feet following non‐grain crops with R² values of 0.875 and 0.821 respectively.     

Alternatives for Nitrogen Diagnosis for Wheat with Different Yield Potentials in the Humid Pampas of Argentina

A correct determination of nitrogen (N) fertilization thresholds in wheat that is based on objective yield produces efficient use of this nutrient. Nitrogen fertilization recommendations for traditional wheat require determination of nitrate (NO₃ ^?)-N availability at 60 cm deep at planting time. However, this methodology is complicated, expensive, and time-consuming; thus, the determination of NO₃ ^?-N level at a lesser depth and at a different time would be desirable. The goals of this work were to determine available N in soil thresholds for traditional and French germplasm wheats and the feasibility of diagnosing N requirements by measuring NO₃ ^?-N at 40 cm deep, at planting or tillering times, in the southeastern Pampas. The experiments were factorial combinations of N rates and fertilization times (planting and tillering) at different sites and years during 2002–2006. Nitrogen fertilization significantly increased grain yield and protein content. French varieties presented greater grain yield (23%), lower protein content (11%), and greater yield per N unit, indicating greater N-use efficiency (NUE) than traditional varieties. A similar relationship was determined between grain yield and available N at both sampling depths. This might be explained by the strong association between NO₃ ^?-N content at 60 and 40 cm deep at both sampling dates. Maximum yield and available N determined at 60 or 40 cm soil deep showed that thresholds were lower for tillering than for planting, regardless of the genotype (152 and 174 kg of available N, respectively). Available N thresholds for 95% of maximum yield were less at 0–40 cm deep than at 0–60 cm deep (10 and 14 kg N ha^?1 for traditional and French genotypes, respectively). The results of this experiment suggest the possibility of diagnosing N requirements for wheat by measuring NO₃ ^?-N content at 40 cm deep, instead of the usual 60 cm, for both traditional and French genotypes.     

Rate of nitrapyrin and soil ph effects on nitrification of ammonium fertilizer and growth and composition of burley tobacco

Abstract

Laboratory and greenhouse experiments were conducted to determine the effects of rate of nitrapyrin and soil pH on nitrification of NH₄ ⁺ fertilizer in soil, and growth and chemical composition of burley tobacco (Nicotiana tabacum L. cv. ‘KY ‐14'). Such experiments were needed to develop information for increasing efficiency of N fertilizer use and to lessen the fertilizer‐induced soil acidity and salt effects on tobacco plants.

Results for laboratory and greenhouse incubations indicated that nitrification proceeeded slowly below pH 5.0 and the nitrapyrin necessary to delay nitrification increased with both increasing soil pH and length of incubation time. Generally, nitrification could be delayed 30 days by nitrapyrin rates of 0.25 or 0.5 μg g^‐1 regardless of soil pH. but rates of 1 μg g^‐1 nitrapyrin or higher were required for 60 days and longer incubation times, particularly at higher soil pH.

Growth and morphology of tobacco plants were either unaffected, or affected positively, by low rates of nitrapyrin (up to 2 μg g^‐1). However, rates of 4 μg g^‐1 and above reduced total plant dry weight, reducing sugars and contents of mineral elements. Concentrations and content of plant NO₃ ^‐ N and Mn were greatly decreased by application of nitrapyrin. Values for most parameters measured increased with increasing soil pH. The data show that low rates of nitrapyrin may be used to alter the ratio of NO₃ ^‐ to NH₄ ⁺ N absorbed by tobacco and possibly improve growth and safety of tobacco.     

Diagnosing nitrogen fertilization requirements of cereals in less than 30 seconds

Abstract

Stems of barley and wheat plants of wide range in nutritional status were analysed for sap NO₃ concentration at the tillering stage using both “Merckoquant”; nitrate test strips and a specific‐ion nitrate electrode. Even though the “Merckoquanf'test strips used in this study did not give precise NO₃ readings they were found to be a satisfactory method for determining the NO₃ content of stems of cereals, and can be used in situ by farmers to predict the necessity of N fertilization for maximum grain yield. If the NO₃ sensitive area on the test strip is coloured to match the standard 500 ppm NO₃ colour in less than 30 seconds, after the application of sap, this is an indication of adequate N nutrition. If the 500 ppm NO₃ colour standard is reached between 30 to 60 seconds, then this is an indication of intermediate N nutrition and fertilization is recommended only under favorable weather conditions. If colour development of the test strip for the 500 ppm N0₃ standard takes more than 60 seconds, or the colour developed does not reach this standard, this is an indication of deficient N nutrition. Therefore, the use of the “Merchoquant”; test strips offers a useful tool in deciding if N fertilization of small‐grain cereals is needed.     

Influence of inorganic soil N,yield potential,and market class on irrigated spring wheat response to N

Abstract

Fertilizer N recommendations for small grains are frequently based on soil test N but data is limited for irrigated spring wheat. The relative grain yield response of irrigated spring wheat to N as affected by inorganic soil N (NO₃‐N and NH₄‐N), yield potential and market class was evaluated in thirteen Southern Idaho field experiments involving N rates. Experiments were conducted on silt loam soils from 1978 to 1986. Preplant soil NO₃‐N and NH₄‐N to a depth of 60 cm and ranging from 27 to 142 kg/ha accounted for approximately 73% of the relative yield variability. NO₃‐N and NH₄‐N were significantly correlated (r=.72). NH₄‐N with NO₃‐N did not account for more of the relative yield variability than using NO₃‐N alone.

Inorganic N in the first 30 cm and the second 30 cm were significantly correlated (r=.69) but N in the first depth increment accounted for more of the relative yield variability. The linear regression coefficient relating inorganic N in the first 30 cm to relative yield of unfertilized spring wheat was almost twice as high as the coefficient for the second 30 cm increment (.50 vs .27). Results indicate that inorganic N below 30 cm should be weighted differently than N in the first 30 cm when determining the N requirements of irrigated spring wheat.

Yield potential significantly affected the relative yield response to N. The response to N was not significantly affected by spring wheat market class (hard red vs soft white).

For estimating fertilizer N requirements, the results provide little justification for the current widespread practices of (1) using the combined NH₄‐N and NO₃‐N inorganic soil test N values when NO₃‐N alone has as much predictive value and (2) assigning equal weight to inorganic soil N at all sampling depths.     

Tillering,nutrient accumulation,and yield of winter wheat as influenced by nitrogen form 1

When grown with mixtures of nitrate‐nitrogen (NO₃‐N) and ammonium‐nitrogen (NH₄‐N) (mixed N) spring wheat (Triticum aestivum L.) plants develop higher order tillers and produce more grain than when grown with only NO₃. Because similar work is lacking for winter wheat, the objective of this study was to examine the effect of N form on tillering, nutrient acquisition, partitioning, and yield of winter wheat. Plants of three cultivars were grown to maturity hydroponically with nutrient solutions containing N as either all NO₃, all NH₄, or an equal mixture of both forms. At maturity, plants were harvested; separated into shoots, roots, and grain; and each part analyzed for dry matter and chemical composition. While the three cultivars varied in all parameters, mixed N plants always produced more tillers (by a range of 16 to 35%), accumulated more N (28 to 61%), phosphorus (P) (22 to 80%), and potassium (K) (11 to 89%) and produced more grain (33 to 60%) than those grown with either form alone. Although mixed N‐induced yield increases were mainly the result of an increase in grain bearing tillers, there was cultivar specific variation in individual yield components (i.e., tiller number, kernels per tiller, and kernel weight) which responded to N form. The presence of NH₄ (either alone or in the mixed N treatment), increased the concentration of reduced N in the shoots, roots, and grain of all cultivars. The effect of NH₄ in either treatment on the concentrations of P and K was variable and depended on the cultivar and plant part. In most cases, partitioning of dry matter, P, and K to the root decreased when NH₄ was present, while partitioning of N was relatively unaffected. Changes in partitioning between the shoot and grain were affected by N treatment, but varied according to cultivar. Based on these data, the changes in partitioning induced by NH₄ and the additional macronutrient accumulation with mixed N are at least partially responsible for mixed‐N‐induced increases in tillering and yield of winter wheat.     

Midrib nitrate concentration as a means for determining nitrogen needs of cabbage

Plant analysis has been used to evaluate the nutritional status of many crops for diagnostic and corrective purposes. This study was initiated to establish critical nitrogen (N) plant tissue levels using midrib NO₃‐N concentration for cabbage (Brassica oleracea L., capitata group) during the growing season. Tissue samples for nitrate analysis were taken from cabbage plants over a period of four growing seasons beginning at the 4 to 6 leaf stage of growth and biweekly through pre‐harvest. The midrib from the most recently full sized leaf was sampled for NO₃‐N concentration determination.

A high degree of correlation existed between NO3‐N concentration in cabbage midribs at various sampling dates and yield as determined by stepwise regression analysis. Nitrate‐N concentration in cabbage midribs indicated the N status of the plant. Minimum or critical levels of NO₃‐N in cabbage midribs for sampling dates throughout the growing season were established for conditions such as are found in the desert regions of Arizona as follows: 4 to 6 leaves, 11,000 mg kg^‐1; 10 to 12 leaves, 8000 mg kg^‐1; folding, 6000 mg kg^‐1; early head, 4000 mg kg^‐1; pre‐harvest, 3000 mg kg^‐1.     

Interacting effects of topsoil water and nitrogen supply on subsoil aluminium toxicity

Abstract

The interacting effects between topsoil water supply, nitrogen (N) placement and subsoil aluminum (Al) toxicity on wheat growth were studied in two split‐root pot experiments. The native nitrate‐N (NO₃‐N) in the topsoil used in each experiment differed and were designated as high (3706 μM) and low (687 μM) for experiments one and two, respectively. Wheat was grown in pots that enabled the root system to be split so that half of the roots were in topsoil and the other half were in subsoils containing varying concentrations of soluble Al. Treatments were imposed which varied the supply of water to the topsoil (either ‘wet’ or ‘dry'). Placement of applied N in either the topsoil or subsoil had little effect on either shoot or root fresh weight, or on the length of roots produced in the subsoil section of the split pots. When water supply to the topsoil was decreased, both shoot and root growth of wheat declined and the yield decrease increased with subsoil Al. In the high‐N experiment, wheat grown in the low Al subsoil with the high native soluble subsoil (NO₃ (3002 μM) was able to exploit the N and subsoil water, hence both shoot and root growth increased considerably in comparison to shoot and root growth of wheat grown in soils containing higher concentrations of subsoil Al. When the native NO₃ was lower (i.e. the low‐N experiment) inadequate root proliferation restricted the ability of plants to use subsoil N and water irrespective of subsoil Al. The results from this study suggest that wheat, grown on yellow earths with Al‐toxic subsoils, will suffer yield reductions when the topsoil dries out (e.g. in the spring when winter rainfall ceases) because subsoil reserves of water and nitrogen are under utilised.     

Sap test to determine nitrate‐nitrogen concentrations in aboveground biomass of winter cover crops

Abstract

In the San Luis Valley of south central Colorado, winter cover crops (WCC) are used to reduce soil erosion and scavenge residual soil‐N. Some San Luis Valley farmers are beginning to use WCC as a source of over‐winter or early‐spring grazing. Common WCC used by farmers, wheat (Triticum aestivum L.) and rye (Secale cereale L.) are reported to accumulate high levels of nitrate nitrogen (NO₃ ^‐‐N) in aboveground biomass that can be toxic to animals. Evaluation and calibration of a quick Cardy Meter² Sap Test (CMST) for determination of NO₃ ^‐‐N status in the field will facilitate the management of these WCC. Field and growth chamber studies were conducted to correlate the CMST with laboratory procedures and with plant and soil parameters. In field and growth chamber studies, the CMST was correlated with standard dry tissue NC₃ ^‐‐N laboratory analysis (P<.001) and with soil inorganic N content (P<.05). These field and growth chamber studies show that the CMST can be a tool in helping farmers identify fields where WCC aboveground biomass is accumulating potentially toxic levels of NO₃ ^‐‐N. Additionally, plant parameters such as nitrogen uptake, biomass, and grain yield of WCC grown under growth chamber conditions were correlated with the CMST readings conducted at the growth stage, Feekes five (P<.05). The growth chamber results suggest that if WCC are grown for grain production, the CMST can help identify the needs for additional nitrogen (N) fertilizer application at Feekes five.     

Mid-Season Prediction of Wheat-Grain Yield Potential Using Plant,Soil, and Sensor Measurements

ABSTRACT

The components that define cereal-grain yield potential have not been well defined. The objective of this study was to collect many differing biological measurements from a long-term winter wheat (Triticum aestivum L.) study in an attempt to better define yield potential. Four treatments were sampled that annually received 0, 45, 90, and 135 kg N ha^?1 at fixed rates of phosphorus (P) (30 kg ha^?1) and potassium (K) (37 kg ha^?1). Mid-season measurements of leaf color, chlorophyll, normalized difference vegetative index (NDVI), plant height, canopy temperature, tiller density, plant density, soil moisture, soil NH₄-N, NO₃-N, organic carbon (C), total nitrogen (N), pH, and N mineralization potential were collected. In addition, soil texture and bulk density were determined to characterize each plot. Correlations and multiple linear-regression analyses were used to determine those variables that can predict final winter wheat grain yield. Both the correlation and regression analyses suggested mid-season NDVI, chlorophyll content, plant height, and total N uptake to be good predictors of final winter wheat grain yield.     

Recovery of soil nitrate by Kjeldahl analysis

Abstract

Recovery of ¹⁵N‐labeled and non‐labeled NO₃ ^‐‐N (100 μg) during total N determination by a semimicro‐Kjeldahl procedure, not modified to include NO₃ ^‐‐N quantitatively, was studied in the presence and absence of soils varying in organic C. Recovery of NO₃ ^‐‐N was negligible in non‐soil systems, irrespective of whether water was present or not, unless an oxidizable C source, octyl alcohol (0.04 g), was added to the digestion mixture; addition of octyl alcohol resulted in a recovery of 78 and 87 μg NO₃ ^‐‐N in the presence and absence of water, respectively. Recovery of 100 μg NO₃ ^‐‐N added to soils containing from 0.1 to 3.8 g of C/cg of soil ranged from 34 to 90 pg NO₃ ^‐‐N in the absence of water. The recovery of the added NO₃ ^‐‐N was in the same order, but not proportional to, the organic C content of these soils. Addition of soil NO₃ ^‐‐N, determined by a separate method of analysis, to a regular Kjeldahl‐N value is not a satisfactory method for determining total soil N.     

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.     

Nitrogen mineralization indicators under semi-arid and semi-humid conditions: influence on wheat yield and nitrogen uptake

The objectives were i) to assess indicators for potential nitrogen (N) mineralization and ii) to analyze their relationships for predicting winter wheat (Triticum aestivum L.) growth parameters (yield and N uptake, N_up) in Mollisols of the semi-arid and semi-humid region of the Argentine Pampas. Thirty-six farmer fields were sampled at 0–20 cm. Several N mineralization indicators, wheat grain yield and N_up at physiological maturity stage were assessed. A principal component (PC) analysis was performed using correlated factors to grain yield and N_up. The cluster analysis showed two main groups: high fertility and low fertility soils. In high fertility soils, combining PCs in multiple regression models enhanced the wheat yield and N_up prediction significantly with a high R² (adj R² = 0.71–0.83). The main factors that explained the wheat parameters were associated with water availability and N mineralization indicator, but they differ according to soil fertility.

Abbreviations: N: nitrogen; SOM: soil organic matter; POM: particulate organic matter; SOC: soil organic carbon; SON: soil organic nitrogen; POM-C: particulate organic carbon; POM-N: particulate organic nitrogen; N_an: anaerobic nitrogen; N_hyd: hydrolyzable N; NO₃-N: cold nitrate; N₂₀₅: N determined by spectrometer at 205 nm; N₂₆₀: N determined by spectrometer at 260 nm; Pe: extractable P; N_up: wheat N uptake; NO₃-N: inorganic N in the form of nitrate; FR: fallow rainfalls (March-Seeding rainfall); FLR: flowering rainfalls (October-December rainfall); GFR: grain filling rainfall (November rainfall); CCR: crop growing season rainfall (June-December rainfall); PCA: principal component analysis; PC: principal component; MR: multiple regression     

Effects of nitrogen fertilization on pot‐grown wheat photosynthate partitioning within intensively farmed soil determined by 13C pulse‐labeling

Understanding rhizodeposited carbon (C) dynamics of winter wheat (Triticum aestivum L.) is important for improving soil fertility and increasing soil C stocks. However, the effects of nitrogen (N) fertilization on photosynthate C allocation to rhizodeposition of wheat grown in an intensively farmed alkaline soil remain elusive. In this study, pot‐grown winter wheat under N fertilization of 250 kg N ha^?1 was pulse‐labeled with ¹³CO₂ at tillering, elongation, anthesis, and grain‐filling stages. The ¹³C in shoots, roots, soil organic carbon (SOC), and rhizosphere‐respired CO₂ was measured 28 d after each ¹³C labeling. The proportion of net‐photosynthesized ¹³C recovered (shoots + roots + soil + soil respired CO₂) in the shoots increased from 58–64% at the tillering to 86–91% at the grain‐filling stage. Likewise, the proportion in the roots decreased from 21–28% to 2–3%, and that in the SOC pool increased from 1–2% to 6–7%. However, the ¹³C respired CO₂ allocated to soil peaked (17–18%) at the elongation stage and decreased to 6–8% at the grain‐filling stage. Over the entire growth season of wheat, N fertilization decreased the proportion of net photosynthate C translocated to the below‐ground pool by about 20%, but increased the total amount of fixed photosynthate C, and therefore increased the below‐ground photosynthate C input. We found that the chase period of about 4 weeks is sufficient to accurately monitor the recovery of ¹³C after pulse labeling in a wheat–soil system. We conclude that N fertilization increased the deposition of photoassimilate C into SOC pools over the entire growth season of wheat compared to the control treatment.     

Effects of solid phase from pig slurry on soil chemical characteristics,nitrate leaching,composition, and yield of wheat

A two years lysimeter experiment was carried out using wheat plants (Triticum aestivum L. cv. Lotti) on two texturally contrasting soils. The main purpose of this study was to evaluate the influence of increasing applications (5,10, 15,20, and 25 t.ha^‐1) of solid phase (SP) from pig slurry on soil nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) content, nitrate‐N (NO₃‐N) leaching as well as on wheat composition and yield. As the control, a basic dressing of NPK fertilizer was applied. Results showed that plant growth was stimulated by increasing amounts of SP, yet the additions of 15 to 20 t SP ha^‐1 led to similar effects on yield as that for the control. An accumulation of P on both soils was observed as well as a significant increase on NO₃‐N leaching due to increasing rates of SP added to the soils. The N and P content in wheat plants (straw and grain) increased with increasing rates of applied SP.