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1.
Abstract

Spatial variability of soil nutrients is known to exist at distances of less than 1 m. Recently, an on‐the‐go system for application of nitrogen (N) fertilizer based on spectral measurements known as in‐season estimated yield (INSEY) improved N use efficiency (NUE) by as much as 17% in winter wheat. Six trials were conducted in 2001, 2002, and 2003 at Ardmore and Burneyville, OK, with an objective to develop an index similar to INSEY for use in predicting yield potential in bermudagrass (Cynodon dactylon L.) that can be used for adjusting fertilizer N rates. Initial results indicate that 55% of variation in predicted bermudagrass forage yield was explained by a Bermudagrass–INSEY (B‐INSEY) index and 54% of the variation in forage N uptake was explained using the normalized difference vegetative index (NDVI). The remaining challenge is to develop appropriate N fertilizer rates based on this information and apply these rates using on‐the‐go technology.  相似文献   

2.
Before sensor‐based variable rate technology (VRT) can be used to reduce nitrogen (N) fertilizer rates in winter wheat (Triticum aestivum L.) spectral radiance readings must be understood. One prominent issue is the impact of crop growth stage on spectral radiance readings, and the ensuing problem of relating databases gathered at different locations and different stages of growth. In order to evaluate the impact of growth stage on spectral radiance, sensor readings were taken from a winter wheat variety trial and two long‐term N and phosphorus (P) fertility trials. The normalized difference vegetative index was computed using red and near infrared (NIR) spectral radiance measurements [NDVI=(NIR‐red)/(NIR+red)]. TotalNuptake in winter wheat at Feekes growth stages 4, 5, 7, and 8 was highly correlated with NDVI. In the variety trial, non‐significant differences in ND VI readings were noticed between the five common genotypes (by growth stage) grown in this region. However, slopes from linear regression of total N uptake on NDVI were different at different stages of growth, which suggests the need for growth stage specific calibration. Freeze injury (altered tissue color) affected the relationship between total N uptake and NDVI, however, NDVI continued to be a good predictor of in‐season total N uptake in wheat even though cell blasting altered tissue color. This work showed that NDVI is a good predictor of biomass, but not necessarily total N concentration in plant tissue. The amount of variability in total N uptake as explained by NDVI increased with advancing growth stage (Feekes 4 to 7), largely due to an increased percentage of soil covered by vegetation.  相似文献   

3.
Nitrogen (N) and phosphorus (P) are major limiting nutrient elements for crop production and continued interest lies in improving their use efficiency. Spectral radiance measurements were evaluated to identify optimum wavelengths for dual detection of N and P status in winter wheat (Triticum aestivum L.). A factorial treatment arrangement of N and P (0, 56, 112, and 168 kg N ha‐1 and 0, 14.5, and 29 kg P ha‐1) was used to further study N and P uptake and associated spectral properties at Perkins and Tipton, Oklahoma. A wide range of spectral radiance measurements (345–1, 145 nm) were obtained from each plot using a PSD 1000 Ocean Optics fiber optic spectrometer. At each reading date, 78 bands and 44 combination indices were generated to test for correlation with forage biomass and N and P uptake. Additional spectral radiance readings were collected using an integrated sensor which has photodiode detectors and interference filters for red and NIR. For this study, simple numerator/denominator indices were useful in predicting biomass, and N uptake and P uptake. Numerator wavelengths that ranged between 705 and 735 nm and denominator wavelengths between 505 and 545 nm provided reliable prediction of forage biomass, and N and P uptake over locations and Feekes growth stages 4 through 6. Using the photodiode sensor, NDVI [(NIR‐red)/(NIR+red)] and NR [(NIR/red)], were also good indices to predict biomass, and N and P uptake. However, no index was found to be good for detecting solely N and P concentration either using the spectrometer or photodiode sensor.  相似文献   

4.
Recent development in canopy optical‐sensing technology provides the opportunity to apply fertilizer variably at the field scale according to spatial variation in plant growth. A field experiment was conducted in Ottawa, Canada, for two consecutive years to determine the effect of fertilizer nitrogen (N) input at variable‐ vs. uniform‐application strategies at the V6–V8 growth stage, on soil mineral N, canopy reflectance, and grain yield of maize (Zea mays L.). The variable N rates were calculated using an algorithm derived from readings of average normalized difference vegetation index (NDVI) of about 0.8 m × 4.6 m, and N fertilizer was then applied to individual patches of the same size of NDVI readings (0.8 m × 4.6 m) within a plot (2184 m2). Canopy reflectance, expressed as NDVI, was monitored with a hand‐held spectrometer, twice weekly before tasseling and once a week thereafter until physiological maturity. Soil mineral N (0–30 cm depth) was analyzed at the V6 and VT growth stages. Our data show that both variable and uniform‐application strategies for N side‐dressings based on canopy‐reflectance mapping data required less amount of N fertilizer (with an average rate of 80 kg N ha–1 as side‐dressing in addition to 30 kg N ha–1 applied at planting), and produced grain yields similar to and higher nitrogen‐use efficiency (NUE) than the preplant fully fertilized (180 kg N ha–1) treatment. No difference was observed in either grain yield or NUE between the variable‐ and uniform‐application strategies. Compared to unfertilized or fully fertilized treatments, the enhancements in grain yield and NUE of the variable‐rate strategy originated from the later N input as side‐dressing rather than the variation in N rates. The variable‐rate strategy resulted in less spatial variations in soil mineral N at the VT growth stage and greater spatial variations in grain yield at harvest than the uniform‐rate strategy. Both variable‐ and uniform‐application strategies reduced spatial variations in soil mineral N at the VT stage and grain yield compared to the unfertilized treatment. The variable‐rate strategy resulted in more sampling points with high soil mineral N than the uniform‐rate strategy at the VT stage.  相似文献   

5.
Soil reflectance affects spectral irradiance measurements taken in winter wheat at early stages of growth when percent cover is low. The objective of this study was to determine the critical percent vegetation coverage needed for forage nitrogen (N) uptake calibration with indirect spectral irradiance measurements. Two field experiments were conducted at Tipton and Perkins, OK in October 1996. The effect of row spacing (15.2, 19.0, 25.4, and 30.5 cm) and growth stage (Feekes 4 and 5) under various N fertilizer rates (0, 56, 112, and 168 kg N ha‐1) on spectral irradiance measurements from wheat was evaluated. The normalized difference vegetative index (NDVI) was used to characterize wheat canopy irradiance. In general, NDVI decreased with increasing row spacing and increased with N fertilizer rate at Feekes growth stage 4. Row spacing and N rate were independent of each other since no significant interaction was found. High correlation (r=0.81–0.98) was observed between NDVI and vegetation coverage. Percent vegetation coverage was a good predictor of the other dependent variables including forage dry matter, and total N uptake, which could indirectly be determined using NDVI. The coefficients of variation (CV's) from NDVI values decreased with increasing vegetation coverage suggesting that less variable NDVI values (CV less than 10%) might be obtained from plots where vegetation coverage exceeds 50%.  相似文献   

6.
The resolution at which variability in soil test and yield parameters exist is fundamental to the efficient use of real-time sensor-based variable rate technology. This study was conducted to determine the optimum field element size for maximum yields in winter wheat (Triticum aestivum L.), using variable nitrogen (N) rates based on sensor readings. The effect of applying N at four different resolutions (0.84, 3.34, 13.38, and 53.51 m2) on grain yield, N uptake and efficiency of use was investigated at Haskell, Hennessey, Perkins, and Tipton, Oklahoma. At Feekes growth stage 5 an optical sensor developed at Oklahoma State University measured red (670 ± 6 nm) and near-infrared (NIR, 780 ± 6 nm) reflectance in each subplot. A normalized-difference-vegetative-index (NDVI) was calculated from the sensor measurements. Nitrogen was applied based on a NDVI–N rate calibration. Nitrogen rate, yield, N uptake, and efficiency of use responses to treatment resolution and applied N fertilizer differed in the 3 years of this experiment. In the first year, no significant influence of resolution on N rate, yield, N uptake, or efficiency of use was observed, likely a result of a late freeze that drastically reduced yields. In the second year of the experiment, there was a trend for a lower N rate and a higher efficiency of use for the 0.84 m2 resolution. In the third year of this study, there was a trend for a higher yield and a higher efficiency of use for the 53.51 m2 resolution at both sites. In general, the finer resolutions tended to have increased efficiency of use in high yielding environments (>2300 kg ha?1), and decreased yields in low yielding environments. This study indicates that application of prescribed fertilizer rates based on spatial variability at resolutions finer than 53.51 m2 could lead to increased yields, decreased grower costs, and decreased environmental impact of excess fertilizers.  相似文献   

7.
Abstract

Nitrogen applications to dallisgrass grown on Olivier silt loam, an Aquic Fragiudalf, increased forage yield, forage digestibility, nutrient concentrations and nutrient contents as N rates increased to 896 kg ha‐1. Expressing yield as a function of N application rate resulted in quadratic prediction equations that accounted for 75 to 98% of the variability in yield during five years. Eighty‐six percent of the maximum yield was obtained during the five years at 448 kg of N ha‐1. Plant concentrations of N, Ca and Mg were increased more than concentrations of the other macronutrients as N rates increased. Plant contents of N, Ca and Mg in the forage increased 4.0, 3.2 and 3.5‐fold as N rates increased to 448 kg ha‐1, while that of P, K and S increased 2.5 to 2.8‐fold. Residual N accumulations in the soil profile were apparent at the 896 kg ha‐1 rate at the end of the growing seasons but were not detected the following March, indicating N losses by leaching and/or denitrification occurred at that N rate. Phosphorus applications increased forage P concentrations but did not increase forage yield nor available P levels in the surface 15 cm of soil. Maximum yields were obtained at forage P concentrations and Bray No. 2 soil P levels as low as 2.0 g kg‐1 and 17 mg kg‐1, respectively.  相似文献   

8.
The primary constraint of predicting the economic optimum nitrogen rate (EONR) for corn (Zea mays L.) is the high variability of soil nitrogen (N) supply due to environments, soil types, manure, and cropping histories. Portable instruments have been developed to measure leaf and canopy optical characteristics for determining plant N status. The objectives of this field study were to: (1) evaluate leaf and canopy optical properties including transmittance, reflectance, and fluorescence as indicators of corn N status with soil types, developmental stages, and N‐application rates, (2) compare the efficiency of two commercial radiometers that are designed to measure canopy reflectance, and (3) assess the constraints of these crop‐based indicators as a possible guide for real‐time N sidedressing in corn. Field experiments with different levels of N, soil types, and corn hybrids were conducted at three sites in Ottawa, ON, Canada, in 2004 and 2005. Leaf chlorophyll concentrations (SPAD chlorophyll meter), chlorophyll fluorescence (OS‐30), leaf area, and canopy reflectance (NDVI measured by CropScan and GreenSeeker radiometers) were simultaneously measured at several growth stages, while grain yield was determined at harvest. Our results show that canopy reflectance (NDVI) displayed similar efficiency as an indicator of N status on both soil types and corn hybrids in the two consecutive years. The chlorophyll readings often differentiated N‐deficient from N‐sufficient plots and therefore were a promising indicator for predicting corn N requirements. The fluorometer device evaluated in this study was unable to characterize corn N status.  相似文献   

9.
Abstract

Sensor‐based technologies for in‐season application of nitrogen (N) to winter wheat (Triticum aestivum L.) have been developed and are in use in the southern Great Plains. Questions arise about the suitability of this technology for spring wheat production in the northern Great Plains. A field experiment was established in Brookings, SD, to evaluate the GreenSeeker Hand Held optical sensor (NTech Industries, Ukiah, CA) for predicting in‐season N status on three spring wheat cultivars (Ingot, Oxen, and Walworth) across five N treatments. Nitrogen rates were 0, 34, 68, 102, and 136 kg N ha?1 applied preplant as ammonium nitrate. Sensor readings and plant biomass samples were collected at Feekes 6 and Feekes 10 growth stages. The sensor measures reflectance in the red and near infrared (NIR) regions of the electromagnetic spectrum. A normalized difference vegetation index (NDVI) was calculated. The ability of the sensor readings to predict biomass, plant N concentration, and plant N uptake for each sampling date was determined. In general, biomass, plant N concentration, and N uptake increased with increasing N rate for both sampling dates. Readings collected at Feekes 6 and Feekes 10 showed a significant relationship with plant biomass, N concentration, and N uptake for all varieties. Plant N uptake and NDVI resulted in a higher regression coefficients compared to biomass and plant N concentration for all varieties. Results suggest that existing sensor‐based variable nitrogen technology developed for winter wheat could be utilized in the northern Great Plains for estimating in‐season N need for spring wheat.  相似文献   

10.
Current methods of determining nitrogen (N) fertilization rates in winter wheat (Triticum aestivum L.) are based on farmer projected yield goals and fixed N removal rates per unit of grain produced. This work reports on an alternative method of determining fertilizer N rates using estimates of early-season plant N uptake and potential yield determined from in-season spectral measurements collected between January and April. Reflectance measurements under daytime lighting in the red and near infrared regions of the spectra were used to compute the normalized difference vegetation index (NDVI). Using a modified daytime lighting reflectance sensor, early-season plant N uptake between Feekes physiological growth stages 4 (leaf sheaths lengthen) through 6 (first node of stem visible) was found to be highly correlated with NDVI. Further analyses showed that dividing the NDVI sensor measurements between Feekes growth stages 4 and 6, by the days from planting to sensing date was highly correlated with final grain yield. This in-season estimate of yield (INSEY) was subsequently used to compute the potential N that could be removed in the grain. In-season N fertilization needs were then considered to be equal to the amount of predicted grain N uptake (potential yield times grain N) minus predicted early-season plant N uptake (at the time of sensing), divided by an efficiency factor of 0.70. This method of determining in-season fertilizer need has been shown to decrease large area N rates while also increasing wheat grain yields when each 1m2 area was sensed and treated independently.  相似文献   

11.
《Journal of plant nutrition》2013,36(10):2285-2294
ABSTRACT

Inorganic soil profile nitrogen (N) levels can increase with application rates greater than those necessary for maximum cereal grain yields. Forage systems are different than grain production systems in that harvest is generally prior to anthesis and gaseous plant N loss is not allowed to occur. This promotes removal of more total N from the system and results in higher nitrogen use efficiencies (NUE).Nitrogen rates representing increased profile N accumulation as well as those below this threshold were evaluated from a long-term rye–wheat–ryegrass production experiment. Nitrogen rates from 1979–1993 were 0, 56, 84, 112, 168, and 224 kg N ha?1.Rates were doubled in 1994 in an effort to add N at a rate above which no increase in forage production would be expected.Wheat was eliminated from the winter seeding mix in 1994, as it was an extremely small portion of the total harvested forage. Deep soil cores (0–366 cm) were taken during the early summer of 1996 from plots with a history of continuous fertilization and forage production since 1979.Cores were split into 15 cm (0–60 cm) or 30 cm increments (60–366 cm) and analyzed for NO3–N, NH4–N, and pH.Total inorganic N accumulations were calculated by adding NO3–N and NH4–N.Surface accumulations of NH4–N were significant with annual N rates of 224 kg N ha?1 or more. No differences in NH4–N were noted at lower depths, thus movement through the profile was not observed. Nitrate–N at the highest N rate was significantly higher than check levels down to 270 cm increasing the risk of groundwater contamination.It should be noted that the maximum N rate was increased to 448 kg ha?1 in 1994 in an attempt to determine a level above which no yield response would be noted. No increase in forage production has been consistently noted with rates over 224 kg N ha?1 and at this level the only adverse effect is increased NO3–N in the surface 90 cm. These long-term experimental results support the conclusion that nitrogen fertilizer additions at recommended rates do not increase the risk of NO3–N leaching.  相似文献   

12.
Abstract

Pearl millet and annual ryegrass were continually doubled‐cropped on Olivier silt loam soil for seven years at six levels of N, applied as ammonium nitrate in three applications to millet and in two applications to ryegrass. Forage yields increased as N application rates increased. During seven years at the 0 and 448 kg/ha N rate, millet produced 35% and 95%, respectively, as much yield as it produced at the 800 kg/ha N rate, while comparable values for ryegrass were 19% and 83%. At 448 kg/ha of N the two grasses produced a combined yield of over 20 Mg/ha of dry forage per year. Ryegrass yields following millet were consistently lower than yields previously obtained at this site.

Nitrogen applications consistently increased concentrations of N, Ca, and Mg in both forage grasses, while effects on P and K were variable and S concentrations were unaffected. The amounts of all nutrients removed in the forages were increased as yields increased with N application rates. Nitrate‐N levels considered to be toxic to ruminant animals occurred only where N applications exceeded 170 kg/ha at any one time. In vitro digestibility of each grass was consistently increased by N applications.

The percentage of fertilizer N that was removed in the crops ranged from 66% to 68% for millet and from 35 to 52% for ryegrass as N applications increased up to 448 kg/ha. Residual ammonium and nitrate levels in the top 1.2 m of soil were not increased by N rates of 448 kg/ha or lower. At the 800 kg/ha N‐rate, the apparent N recovery rate decreased and residual ammonium and nitrate levels increased throughout the soil profile.  相似文献   

13.
Abstract

Nitrogen (N) fertilization for cereal crop production does not follow any kind of generalized methodology that guarantees maximum nitrogen use efficiency (NUE). The objective of this work was to amalgamate some of the current concepts for N management in cereal production into an applied algorithm. This work at Oklahoma State University from 1992 to present has focused primarily on the use of optical sensors in red and near infrared bands for predicting yield, and using that information in an algorithm to estimate fertilizer requirements. The current algorithm, “WheatN.1.0,” may be separated into several discreet components: 1) mid‐season prediction of grain yield, determined by dividing the normalized difference vegetative index (NDVI) by the number of days from planting to sensing (estimate of biomass produced per day on the specific date when sensor readings are collected); 2) estimating temporally dependent responsiveness to applied N by placing non‐N‐limiting strips in production fields each year, and comparing these to the farmer practice (response index); and 3) determining the spatial variability within each 0.4 m2 area using the coefficient of variation (CV) from NDVI readings. These components are then integrated into a functional algorithm to estimate application rate whereby N removal is estimated based on the predicted yield potential for each 0.4 m2 area and adjusted for the seasonally dependent responsiveness to applied N. This work shows that yield potential prediction equations for winter wheat can be reliably established with only 2 years of field data. Furthermore, basing mid‐season N fertilizer rates on predicted yield potential and a response index can increase NUE by over 15% in winter wheat when compared to conventional methods. Using our optical sensor‐based algorithm that employs yield prediction and N responsiveness by location (0.4 m2 resolution) can increase yields and decrease environmental contamination due to excessive N fertilization.  相似文献   

14.
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.  相似文献   

15.
 A routine soil testing procedure for soil N mineralization is needed that is rapid and precise. Not accounting for N mineralization can result in the over-application of N, especially in soils with a history of manure application. Our objectives were to compare results from a recently proposed rapid laboratory procedure with: (1) long-term N mineralization under standard laboratory conditions, and (2) actual forage N uptake from soil receiving dairy cattle (Bos taurus) manure in a 2-year field study. The rapid procedure is based on the quantity of CO2-C evolved during 24 h under optimum laboratory conditions following the rewetting of dried soil. Dairy cattle manure was surface applied beginning in 1992 at annual rates of 0, 112, 224, or 448 kg N ha–1 to field plots on a Windthorst fine sandy loam soil (fine, mixed, thermic Udic Paleustalf) near Stephenville, Texas (32°N, 98°W). Results of the one-day CO2 procedure were highly correlated with soil N mineralized from samples collected in March of 1995 (P=0.004) and 1996 (P<0.001) and with forage N uptake (P<0.001) both years of the study. Residual inorganic N in the same soil samples was poorly correlated with soil N mineralization and forage N uptake. Received: 23 February 2000  相似文献   

16.
Abstract

A cotton (Gossypium hirsutum)–peanut (Arachis hypogaea L.) rotation is widely practiced in the southern coastal plain following the reemergence of cotton as a major crop in the 1990s. Very few plant nutrition studies have been conducted in the coastal plain (CP) with modern cotton varieties and none with the cotton–peanut rotation. Experiments with varying rates of nitrogen (N), phosphorus (P), and potassium (K) were conducted to determine if the recommendations from soil tests provide adequate nutrition for maximizing profit when yield goals are Georgia state averages, due to other conditions. From 1996 through 1998, N, P, and K experiments were conducted in cotton crops, and P and K experiments were conducted in peanut crops on Tifton loamy sand. Initial Mehlich‐1 P was 2 to 3 mg/kg (“low”) and Mehlich‐1 K was 50 to 64 mg/kg (“medium” for cotton and “high” for peanut). Each crop was grown each year. State average yields of cotton and peanuts were produced. There was no response in cotton yield to N rates from 34 to 136 kg N/ha. Lack of response may have been due to the fact that the field had not been in production for several years prior to 1996 and there was ample soil mineral N. In 1997 and 1998, residual N provided by N fixation by the previous peanut crop appeared to be sufficient. Maximum profit from P fertilization in cotton was attained at 50 kg P/ha, the recommendation from the soil test. However, a University of Georgia Cooperative Extension Service recommendation to double the P rate for new land with a “low” Mehlich‐1 P soil test was not validated. Cotton yield did not respond to K fertilization even though an application of 55 kg K/ha/year was recommended from the soil test. Peanut yield and grade did not respond to either P or K fertilization. The recommendation from the soil test was 40 kg P/ha/year and no K. Estimates of P removal were 11 kg/ha for cotton and 8 mg/ha for peanut crops. Estimates of K removal were 25 kg/ha for cotton and 22 kg/ha for peanut crops. Over 3 years, soil P was not depleted, but soil K was depleted. Approximately 12 kg P/ha were required to raise soil test P 1 mg/kg and 18 kg K/ha were required to raise soil test K 1 mg/kg (49 lb. P2O5 to increase the P test 1 lb./acre, 38 lb. K2O to raise the K test 1 lb./acre). Additional studies are needed, but the current studies suggest that revisions in recommendations are needed for both cotton and peanut crops.  相似文献   

17.
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   

18.
Abstract

The use of conservation tillage methods, including ridge tillage, has increased dramatically in recent years. At the present time, there is great concern that farmers are applying more nitrogen (N) fertilizer than is environmentally or economically sound. In order to determine if N requirement for optimum yield differs with tillage system, tests were initiated to study tillage and N effects on N content, soil moisture content, and yield of corn (Zea mays L.). The study was established in 1987 on two soil types, an Estelline soil (Pachic Haploboroll) and an Egan soil (Udic Haplustoll), located in eastern South Dakota. Five rates of N (0, 65, 130, 195, and 260 kg ha?1) were applied to plots managed with 3 tillage systems: chisel plow, moldboard plow, and ridge. On the Estelline soil, in both 1988 and 1989, ridge‐tilled plots contained a greater amount of water in the soil profile at emergence and at mid silk than did plots in the other two tillage systems. Soil moisture content at mid silk was significantly correlated with earleaf N, total N uptake, and grain yield in 1988 and earleaf N and grain yield in 1989. However, the correlation coefficients were higher in 1988 than in 1989. On the Egan soil, there were no significant differences in soil moisture content among tillage systems. On the Estelline soil, corn grain yield was affected by a tillage x N‐rate interaction in 1988. Maximum yield within the ridge system was achieved with the 130 kg ha?1 rate. In 1989 on the Estelline soil, yield was affected by tillage and N rate, but there was no interaction between factors. When averaged over N rates, yields were 7.1, 6.6, and 6.5 Mg ha?1 in the ridge, moldboard, and chisel systems, respectively. In 1988 plant total N uptake was greater in the ridge system than the moldboard or chisel systems; in 1989 uptake was affected by N rate alone. On the Egan soil, tillage did not affect soil moisture, total N uptake or grain yield in either year. Corn grain yield increased with increasing N rate up to the 195 kg ha?1 rate. This study indicates that, on some soil types, ridge tillage can improve soil water holding capacity, N utilization and yield of corn.  相似文献   

19.
Abstract

A soil test for mineralizable soil N had been calibrated for winter wheat in the Willamette Valley of western Oregon. Seventy‐eight percent of the variation in spring N uptake by unfertilized wheat was explained by N mineralized from mid‐winter soil samples incubated anaerobically for 7 days at 40°C. Mineralizable N (Nmin) ranged from 10 to 30 mg N kg?1 and was used to predict N fertilizer needs. Recommended rates of N were correlated (R2=0.87) with maximum economic rates of N fertilizer. Subsequent farmer adoption of no‐till sowing and a high frequency of soil tests>30 mg N kg?1 prompted reevaluation of the soil test. Four N fertilizer rates [0, 56, G, and G+56 kg N ha?1] were compared in 12 m×150 m farmer‐managed plots. Grower's N rates (G) ranged from 90 to 180 kg N ha?1 and were based on Nmin and NH4‐N plus NO3‐N soil tests. Averaged across ten no‐till and five conventionally tilled sites, grain yield and crop N uptake were maximized at the recommended rate of N. Results demonstrate that N fertilizer needs for winter wheat can be predicted over a wide range of mineralizable soil N (10 to 75 mg N kg?1) and that the same soil test calibration can be used for conventionally sown and direct‐seeded winter wheat.  相似文献   

20.
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   

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