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1.
Abstract

The experiment was conducted at Kulumsa, South East Ethiopia, using four levels of nitrogen (N) (0, 50,100 and 150?kg N ha?1) and four levels of phosphorus (P) (0, 35, 70 and 105?kg P2O5 ha?1) fertilizers arranged in 4?×?4 factorial arrangements in randomized complete block design with three replications. The available P was increased after harvest due to the application of N and P fertilizer at the rates of 100 or 150?kg N ha?1 and 70 or 105?kg P2O5 ha?1. More specifically, nutrients concentration and nutrient uptake were significantly (p?<?.01) varied among treatment combinations and nutrient use efficiency was declined by increasing N and P after optimum rates. The higher physiological efficiency of N (53.47?kg kg?1) and P (580.41?kg kg?1) and the highest apparent recovery of N (19.62%) and P (2.47%) was recorded from application of 50?kg N ha?1 and P at 70?kg P2O5 ha?1 and the highest agronomic efficiency of N (10.78?kg kg?1) and P (15.25?kg kg?1) was recorded from N at the rate of 50?kg N ha?1 and P at 35?kg P2O5 ha?1, respectively. The combination of N at 100?kg N ha?1 and P at 70?kg P2O5 ha?1 was promising combination that generated highest net benefit 488,878.5 ETB (Ethiopian birr) ha?1 with the highest marginal rate of return (36638%) and gave the highest seed yield (1858.82?kg ha?1) with yield increment of about 57.72% over the control.  相似文献   

2.
Field experiments were conducted at 15 site-years with barley and 10 site-years with oat over five years to determine the relative nitrogen (N) fertilizer requirements of forage versus grain for barley and oat on Black Chernozem (Typic Agricryoll – 6 site-years on barley and 3 site-years on oat) and Gray Luvisol (Typic Haplocryalf – 9 site-years on barley and 7 site-years on oat) soils in central and north-central Alberta, Canada. Barley harvested for forage responded to higher level of applied N than when it was harvested for grain at most site-years. On average for barley, the amount of N fertilizer required to achieve maximum yield of forage was 58 kg N ha?1 greater than that of grain, and also was somewhat greater on Black Chernozem soils than on Gray Luvisol soils. The results for oat were inconclusive, with almost equal numbers of site-years showed higher N requirements for grain as for forage.  相似文献   

3.
ABSTRACT

Grain yield in many soybean experiments fails to respond to fertilizer nitrogen (N). A few positive responses have been reported when soybean were grown in the southern U.S., when N was applied near flowering and when biosolids were added. In a previous study, low N concentrations of soybean forage in north Texas on a high pH calcareous soil were reported and thus, we suspected a N nutrition problem. Consequently, we initiated this study to determine whether selected preplant N sources broadcast and incorporated into a Houston Black clay (fine, smectitic, thermic Udic Haplusterts) might increase forage N concentration, forage yield, or soybean grain yield. In 2003, N was applied as ammonium nitrate (NH4NO3, AN) up to 112 kg N ha? 1 and dairy manure compost (DMC) was applied at rates of 4.9, 9.9, 15.0, and 19.9 Mg ha? 1. The DMC contained 5.9, 2.6, and 6.7 g kg? 1 of total N, P, and K, respectively; thus DMC added 29 to 116 kg N ha? 1. In 2004, AN was applied at rates of 112 and 224 kg N ha? 1 and DMC was applied at 28 and 57 Mg ha? 1; thus, DMC added 168 to 335 kg N ha? 1. In another 2004 test, biosolids, a biosolids/municipal yard waste compost mixture (BYWC), and AN were compared. The biosolids contained 31, 18, and 2.9 g kg? 1 total N, P, and K, respectively. The BYWC mixture contained 8.8, 6.1, and 3.4 g kg? 1 of total N, P, and K, respectively. Biosolids were applied at 10 Mg ha? 1 (310 kg N ha? 1), BYWC was applied at 58 Mg ha? 1 (510 kg N ha? 1), and AN up to 224 kg N ha? 1. None of the soil treatments increased soybean grain yield or forage yield although AN slightly increased forage N concentration in 2003.  相似文献   

4.
Sorghum is cultivated on Vertisols in the Ethiopian Highlands. An experiment was conducted in the Gumara-Maksegnit watershed in 2013 and 2014 to assess the effect of rate and timing of nitrogen fertilizer application on the possibility to shorten the maturity period and to improve the productivity of sorghum. The experiment was laid out as Randomized Complete Block Design with three replications. Treatments were nitrogen doses between 0 and 87 kg N ha?1 as urea applied at planting, at knee-height stage or in split doses at both stages. Results showed that application of 23, 41, 64 and 87 kg ha?1 N gave a yield increase of 40, 53, 62 and 69% over the control (0 kg N ha?1), respectively. In addition, split application of 41 kg ha?1, 64 kg ha?1 and 87 kg ha?1 of nitrogen fertilizer, half at planting and half at knee height stage, gave 19%, 15% and 18% increase in sorghum grain yield over a single dose application, respectively. Applying 87 kg ha?1 nitrogen fertilizer with split application half at planting and half at knee height stage, along with 46 kg ha?1 of P2O5, gave the highest grain yield and income.  相似文献   

5.
Swine lagoon sludge is commonly applied to soil as a source of nitrogen (N) for crop production but the fate of applied N not recovered from the soil by the receiver crop has received little attention. The objectives of this study were to (1) assess the yield and N accumulation responses of corn (Zea mays L.) and wheat (Triticum aestivum) to different levels of N applied as swine lagoon sludge, (2) quantify recovery of residual N accumulation by the second and third crops after sludge application, and (3) evaluate the effect of different sludge N rates on nitrate (NO3-N) concentrations in the soil. Sludge N trials were conducted with wheat on two swine farms and with corn on one swine farm in the coastal plain of North Carolina. Agronomic optimum N rates for wheat grown at two locations was 360 kg total sludge N ha?1 and the optimum N rate for corn at one location was 327 kg total sludge N ha?1. Residual N recovered by subsequent wheat and corn crops following the corn crop that received lagoon sludge was 3 and 12 kg N ha?1, respectively, on a whole-plant basis and 2 and 10 kg N ha?1, respectively, on a grain basis at the agronomic optimum N rate for corn (327 kg sludge N ha?1). From the 327 kg ha?1 of sludge N applied to corn, 249 kg N ha?1 were not recovered after harvest of three crops for grain. Accumulation in recalcitrant soil organic N pools, ammonia (NH3) volatilization during sludge application, return of N in stover/straw to the soil, and leaching of NO3 from the root zone probably account for much of the nonutilized N. At the agronomic sludge N rate for corn (327 kg N ha?1), downward movement of NO3-N through the soil was similar to that for the 168 kg N ha?1 urea ammonium nitrate (UAN) treatment. Thus, potential N pollution of groundwater by land application of lagoon sludge would not exceed that caused by UAN application.  相似文献   

6.
Abstract

A field trial was conducted during the short‐day period of 2004–2005 at Ona, Fl., to study the factorial effect of nitrogen (67, 90, and 134 kg N ha?1) and phosphorus (0, 5, 10, 20, and 40 kg P ha?1) rates on forage dry‐matter yield, quality, nutrient uptake, and leaf pigment concentration of limpograss (Hemarthria altissima). The N and P fertilizers were applied 45 days before each of two harvests. There was no interaction between N and P rates on any of the measured variables. Cool‐season forage yield increased curvilinearly from 137 to 350 kg ha?1 in winter and 237 to 1389 kg ha?1 in early spring, whereas crude protein (CP) concentration increased from 145 to 158 g kg?1, as P was increased from 0 to 40 kg ha?1, but yield and CP were not affected by N rate. There was a decreasing linear relationship between leaf concentration of anthocyanins and P rate of application such that forage obtained with 0 kg P ha?1 had 61% more leaf anthocyanins and purple pigmentation than with 40 kg P ha?1. There was no effect of N on anthocyanins content. It was concluded that increased level of leaf anthocyanins was due to the cumulative stress from cool weather and lower plant‐tissue P levels, which resulted in reduced growth and yield of limpograss. In cool weather, P played a critical role in controlling leaf purple pigmentation and forage yield.  相似文献   

7.
Abstract

Pearl millet is a potential dryland crop for Nebraska. Experiments were conducted in eastern Nebraska in 2000, 2001, and 2002, and in western Nebraska in 2000 and 2001. The objectives were to determine optimum nitrogen (N) rate, N uptake, and N use efficiency (NUE) for pearl millet. The hybrids “68×086R” and “293A×086R” and N rates of 0, 45, 90, and 135 kg N ha?1 were used. Hybrids had similar yield, N uptake and NUE responses. In western Nebraska in 2000, pearl millet yield response to N rate was linear, but the yield increase was only 354 kg ha?1 to application of 135 kg N ha?1. In eastern Nebraska, pearl millet response to N rate was quadratic with maximum grain yields of 4040 in 2001 and 4890 kg ha?1 in 2002 attained with 90 kg N ha?1. The optimum N rate for pearl millet was 90 kg N ha?1 for eastern Nebraska. For western Nebraska, drought may often limit pearl millet's response to N fertilizer.  相似文献   

8.
The optimum dose of nitrogen (N) and phosphorus (P) for Withania somnifera was determined by utilizing graded levels of 0, 30, 45 and 60 kg ha?1 N and 0, 13, 26 and 40 kg ha?1 P in two separate simple randomized pot experiments. Soil-application of 45 kg N ha?1 and 26 kg P ha?1 proved the best dose for increasing shoot and root length, leaf area, fresh and dry weight of shoot and root, total chlorophyll and leaf-N, P, and potassium (K) content, nitrate reductase, and carbonic anhydrase activity, total alkaloid content, seed-yield per plant, root- yield per plant and berries per plant. While 30 kg N ha?1 proved best for root length, fresh and dry weights, as well as root-yield per plant. However, the effect of N and P fertilizers on carotenoid content, seeds per berry and 100-seed weight were insipid. Leaf- P remained unaffected by nitrogen application.  相似文献   

9.
Abstract

To determine the relationships between microbial biomass nitrogen (N), nitrate–nitrogen leaching (NO3-N leaching) and N uptake by plants, a field experiment and a soil column experiment were conducted. In the field experiment, microbial biomass N, 0.5 mol L?1 K2SO4 extractable N (extractable N), NO3-N leaching and N uptake by corn were monitored in sawdust compost (SDC: 20 Mg ha?1 containing 158 kg N ha?1 of total N [approximately 50% is easily decomposable organic N]), chemical fertilizer (CF) and no fertilizer (NF) treatments from May 2000 to September 2002. In the soil column experiment, microbial biomass N, extractable N and NO3-N leaching were monitored in soil treated with SDC (20 Mg ha?1) + rice straw (RS) at five different application rates (0, 2.5, 5, 7.5 and 10 Mg ha?1 containing 0, 15, 29, 44 and 59 kg N ha?1) and in soil treated with CF in 2001. Nitrogen was applied as (NH4)2SO4 at rates of 220 kg N ha?1 for SDC and SDC + RS treatments and at a rate of 300 kg N ha?1 for the CF treatment in both experiments. In the field experiment, microbial biomass N in the SDC treatment increased to 147 kg N ha?1 at 7 days after treatment (DAT) and was maintained at 60–70 kg N ha?1 after 30 days. Conversely, microbial biomass N in the CF treatment did not increase significantly. Extractable N in the surface soil increased immediately after treatment, but was found at lower levels in the SDC treatment compared to the CF treatment until 7 DAT. A small amount of NO3-N leaching was observed until 21 DAT and increased markedly from 27 to 42 DAT in the SDC and CF treatments. Cumulative NO3-N leaching in the CF treatment was 146 kg N ha?1, which was equal to half of the applied N, but only 53 kg N ha?1 in the SDC treatment. In contrast, there was no significant difference between N uptake by corn in the SDC and CF treatments. In the soil column experiment, microbial biomass N in the SDC + RS treatment at 7 DAT increased with increased RS application. Conversely, extractable N at 7 DAT and cumulative NO3-N leaching until 42 DAT decreased with increased RS application. In both experiments, microbial biomass N was negatively correlated with extractable N at 7 DAT and cumulative NO3-N leaching until 42 DAT, and extractable N was positively correlated with cumulative NO3-N leaching. We concluded that microbial biomass N formation in the surface soil decreased extractable N and, consequently, contributed to decreasing NO3-N leaching without impacting negatively on N uptake by plants.  相似文献   

10.
More than 80% of broiler (chicken, Gallus gallus domesticus) litter produced annually is applied as a plant nutrient source, particularly for nitrogen (N) and phosphorus (P), to pastures. However, N losses during the process of litter N mineralization limit availability of N to crops. This study determined broiler litter N and P availability and apparent use efficiency (ANUE, APUE) to bermudagrass [Cynodon dactylon] during the first year after litter application. Treatments consisted of three litter rates (3.3, 6.6, and 13.2 Mg ha?1), a commercial N fertilizer rate that provided 358 kg N ha?1 as ammonium nitrate (NH4NO3), and an untreated control. Results showed bermudagrass dry-matter (DM) yield increased significantly with increase in litter rate. Commercial N fertilizer produced significantly greater DM yield than 3.3 and 6.6 Mg ha?1 of litter but produced less DM yield than 13.2 Mg ha?1 of litter. The overall average of ANUE from litter was 39% compared to the 59% from fertilizer. The mean litter N availabilities to bermudagrass during the first year after litter application were 48.5, 112.5, and 222 kg ha?1, corresponding to the 3.3, 6.6, and 13.2 Mg ha?1 litter rates, respectively. The overall mean of litter N mineralization, which was surface broadcast to bermudagrass plots during the first year, was 59.5% of the total litter N applied. The APUE, averaged across the rate and locations, was 13.6%, which was quite smaller than the ANUE of 39%. This finding of small APUE also validates the potential for P accumulation in soil after long-term animal manure application.  相似文献   

11.
Cereal grain and nitrogen (N) fertilizer prices have varied greatly in recent years. The aim of this study was to determine the optimum dose of N fertilizer needed to maximize revenues of soft red winter wheat in Alava (northern Spain). Economically optimum rates of N application (Nyield) ranged from 142 to 174 kg N ha?1 depending on the price of both N fertilizer and wheat. Growers received an extra income of 0.006 [euro] kg?1 if the grain protein content was greater than 12.5%, with the minimum required N dose to obtain this value (Nprot) being 176 kg ha?1. The extra amount of N fertilizer required over Nyield to reach Nprot ranged from 2 to 34 kg N ha?1, and the extra benefits associated varied from 24 to 36 [euro] ha?1.  相似文献   

12.
It is important to develop integrated fertilization strategies for various crops that enhance the competitive ability of the crop, maximize crop production and reduce the risk of nonpoint source pollution from fertilizers. In order to study the effects of mineral nitrogen fertilization and biofertilizer inoculation on yield and some physiological traits of rapeseed (Brassica napus L.) under different levels of sulfur fertilizer, field experiments in factorial scheme based on randomized complete block design were conducted with three replications in 2012 and 2013. Experimental factors were: (1) four levels of chemical nitrogen fertilizer (0, 100, 150 and 200 kg N ha?1), (2) two levels of biofertilizer (with and without inoculation) consisting Azotobacter sp. and Azospirillum sp. and (3) two levels of sulfur application (0 and 50 kg S ha?1). Rapeseed yield, oil content of grains and studied physiological traits had a strong association with the N fertilization, biofertilizer inoculation and sulfur (S) application. Higher rates of N fertilization, biofertilizer inoculation and S application increased the grain yield of rapeseed. In the case of physiological traits, the highest value of relative water content (RWC) was recorded in 100 kg N ha?1 that was statistically in par with 150 kg N ha?1 application, while usage of 150 kg N ha?1 showed the maximum cell membrane stability (CMS). Inoculation with biofertilizer and S fertilization resulted in higher RWC and CMS in rapeseed plants. The chlorophyll content showed its maximum values in the highest level of N fertilization, biofertilizer inoculation and S application. The usage of 200 kg N ha?1 significantly decreased the oil content of rapeseed grains, but the highest grain oil content was obtained from the application of 150 kg N ha?1, Azotobacter sp. and Azospirillum sp. inoculation and S fertilization. It seems that moderate N rate (about 150 kg N ha?1) and S application (about 50 kg S ha?1) can prove to be beneficial in improving growth, development and total yield of inoculated rapeseed plants.  相似文献   

13.
Field experiments were conducted with four nitrogen fertilizer treatments to study the effects of controlled-release urea combined with conventional urea on the nitrogen uptake, root yield, and contents of protein, soluble sugar, saponin, zinc (Zn), iron (Fe), magnesium (Mg), and copper (Cu) in Platycodon grandiflorum. Field experiments were conducted with four nitrogen (N) fertilizer treatments: no N fertilization; conventional urea with N rate of 175 kg N ha?1; conventional urea with N rate of 160 kg N ha?1; controlled-release urea combined with conventional urea with N rate of 160 kg N ha?1; controlled-release urea combined with conventional urea with N rate of 135 kg N ha?1. The results showed that nitrogen application significantly increased the yield of P. grandiflorum compared with the control. Treatment with controlled-release urea combined with conventional urea at 160 kg N ha?1 provided the highest yield of 7329.58 kg ha?1. Nitrogen application also increased the contents of soluble sugar, total saponin, protein, Zn, Fe, and Mg but decreased Cu content. Protein, saponin, and Zn contents were significantly higher, but Cu content was lower in P. grandiflorum fertilized with controlled-release urea combined with conventional urea than those fertilized with conventional urea alone. The combination of controlled-release urea with conventional urea at 160 kg N ha?1 was the optimal treatment under the experimental condition investigated in this study.  相似文献   

14.
Studies were conducted to evaluate response of dryland corn (Zea mays L.) along the upper Texas Gulf Coast to residual soil nitrate-nitrogen (NO3-N) measured to depths of 15, 30, and 61 cm. Residual soil NO3-N levels ranged from 3.4 to 31.6, 7.8 to 49.3, and 9.0 to 71.7 kg ha?1, respectively, in 0 to 15, 15 to 30, and 30 to 61 cm depth increments, with cumulative NO3-N ranging from 23.5 to 114.5 kg ha?1 across sites-years. Where N fertilizer was reduced due to N crediting, yields and bushel weights at all 13 site-years showed no difference from those receiving full recommended N rates. A yield response to any level of added fertilizer N above the control was observed for only 6 of 13 site-years. These results indicate a high potential for success in crediting carryover soil NO3-N to 61 cm as a means of reducing applied nitrogen fertilizer rates.  相似文献   

15.
Because limited information is available about the validated use of a chlorophyll meter for predicting nitrogen requirements for optimum growth and yield of wheat after application of herbicides, field experiments were carried out in the winter seasons of 2011/2012 and 2012/2013 under different weed and N fertilization treatments. Five weeded treatments, application of herbicides 25 days after sowing (DAS), hand pulling once at 55 DAS and a weedy check were combined with four N application rates. Weeds were completely absent in the non-fertilized plots, either with metribuzin or hand pulling as well as in isoproturon-treated plots fertilized with 190 or 285 kg N ha?1. The grain yield was similar in the treatments of isoproturon × 190 kg N ha?1, isoproturon + diflufenican × conditional N treatment (113.9) or 190 kg N ha?1, hand pulling × conditional N treatment (104.8) or 285 kg N ha?1 and metribuzin × 190 kg N ha?1. Under weeded practices, conditional N treatment recorded the maximum nitrogen use efficiency and almost equaled the grain protein content of the 190 kg N ha?1 application rate. N application based on SPAD readings saved about 40.0% and 44.8% N with isoproturon + diflufenican or hand pulling, respectively, compared to the recommended rate (190 kg N ha?1) without noticeable yield loss.  相似文献   

16.
Bermuda grass [Cynodon dactylon (L.) Pers.] is a major forage for grazing and hay production in the southern United States. The objectives of this study were to determine effects of nitrogen (N) fertilization rate (0, 112, 224, 336, and 448 kg ha?1), split spring and summer applications of N at the 224 and 448 kg ha?1 rates, and harvest periods (spring and summer) on forage yield, crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), total digestible nutrients (TDN), and concentrations of phosphorus (P), potassium (K), magnesium (Mg), and calcium (Ca in Midland Bermuda grass. Data were collected from 2002 to 2008 as part of an ongoing, long-term soil fertility experiment in southern Oklahoma. Repeated measures analysis of these long-term data showed that forage yield responses to N rate varied with year and harvest time with up to 2.5-fold yield differences among years. Nitrogen fertilization increased CP, TDN, and macronutrient P and Mg and decreased ADF and NDF. Crude protein was increased by ≥50%, and ADF and NDF dropped by up to 25% with the greatest N rate. In general, split N applications did not affect forage yield but produced low-quality forage compared to single N application in spring. Split application of 448 kg N ha?1 gave forage with CP, TDN, ADF, and NDF similar to the Bermuda grass receiving 336 or 448 kg N ha?1 as a single application. Spring forage had better forage quality than summer harvests. While N fertilization increased forage Mg and P concentrations by more than 50% during both spring and summer, it had no effect or slight increased K and Ca concentrations. In the southern Great Plains, despite the weather-dependent variability in forage yield of Bermuda grass, N application increase forage quality.  相似文献   

17.
The objective of this study was to determine the effect of nitrogen (N) application source and rate on silage corn (Zea mays L.). Urea, ammonium nitrate, and ammonium sulfate were compared at 50, 100, 150, and 200 kg N ha?1. The application of ammonium sulfate produced the highest plant height, leaf area index (LAI), total yield, and stem, leaf, and ear dry matter, followed by ammonium nitrate and urea. However, nitrogen sources had no marked effects on the content of protein, ash, oil, soluble carbohydrates, acid detergent fiber (ADF) and neutral detergent fiber (NDF). As the rate of nitrogen increased plant height, LAI, total yield, and stem, leaf, tassel, and ear dry matters, and protein, ash and oil contents increased while soluble carbohydrates, ADF, and NDF contents decreased. Ammonium sulfate was the most effective N source on production and 200 kg N ha?1 was the most effective N rate on corn yield and quality.  相似文献   

18.
The method of fertilizer nitrogen (N) application can affect N uptake in tall fescue and therefore its yield and quality. Subsurface-banding (knife) of fertilizer maximizes fescue N uptake in the poorly-drained clay-pan soils of southeastern Kansas. This study was conducted to determine if knifed N results in greater N uptake than the conventional top-dress application method in a deep, well-drained soil of east-central Kansas. The experiment, conducted in a Smolan silty clay loam soil, was a split-plot with fertilizer nitrogen rates 0, 140 and 280 kg N ha?1 applied as urea-ammonium nitrate (UAN, 28% N), knifed or top-dressed. Soil inorganic N [ammonium (NH4)- and nitrate (NO3–N)] and N in roots and plant tops were measured at various times during the growing season. At final harvest, most of the knifed N (99.7%) was accounted for in plant tissue (roots and tops) and soil, with more than half of the knifed N remaining as soil inorganic N. With the top-dressed method, 27% was unaccounted for and presumed lost in gaseous form. Knifing fertilizer N in fescue fields of east-central Kansas will maximize the availability of N, reduce potential N losses, and increase forage quality.  相似文献   

19.
(pp. 825–831)

This study was carried out to clarify the effects of soil nitrate before cultivation and amounts of basal-dressed nitrogen on additional N application rate and yields of semi-forced tomato for three years from 1998 to 2000. The amounts and timing of additional N dressing were determined based on diagnosis of petiole sap nitrate. The top-dressing was carried out with a liquid fertilizer when the nitrate concentration of a leaflet's petiole sap of leaf beneath fruit which is 2–4 cm declined below 2000 mg L?1.

For standard yield by the method of fertilizer application based on this condition, no basal-dressed nitrogen was required when soil nitrate before cultivation was 150 mg kg?1 dry soil or higher in the 0–30 cm layer; 38 kg ha?1 of basal-dressed nitrogen, which corresponds to 25% of the standard rate of fertilizer application of Chiba Prefecture, was optimum when soil nitrate before cultivation was 100150 mg kg?1 dry soil; 75 kg ha?1 of basal-dressed nitrogen, which corresponds to 50% of the standard, was optimum when soil nitrate before cultivation was under 100 mg kg?1 dry soil. A standard yield was secured and the rate of nitrogen fertilizer application decreased by 49–76% of the standard by keeping the nitrate concentration of tomato petiole sap between 1000–2000 mg L?1 from early harvest time to topping time under these conditions.  相似文献   

20.
Abstract

The single‐year response of soil inorganic nitrogen (N) content and indices of red raspberry (Rubus ideaus L.) yield, vigor, and N status to rate and source of fertilizer N were determined. Twenty‐nine trials were conducted in commercial plantings from 1994 to 1996. Treatments were 0, 55, or 110 kg N ha?1 as ammonium nitrate or 55 kg N ha?1 as a slow‐release fertilizer product containing 60% polycoated sulfur‐coated urea and 40% urea. Soil nitrate (NO3) content frequently increased during the growing season, indicating that soil N supply was nonlimiting. The plant indices were generally insensitive to fertilizer‐N rate under these high‐N fertility conditions. Soil nitrate content measured after berry harvest was frequently excessive even at the recommended N rate and can be used to identify fields with excess N fertility. The slow‐release N fertilizer provided limited benefits compared with use of ammonium nitrate.  相似文献   

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