Maturity and quality of alfalfa as affected by phosphorus fertility

Abstract

Environmental stresses adversely affect alfalfa (Medicago sativa L.) forage quality through altered plant development; however, the effects of soil nutrient stress on forage quality are not well known. The objective of this study was to determine what effect low soil phosphorus (P) had on alfalfa forage quality. Three preplant incorporated rates of P (0, 29, or 59 kg/ha) followed by five topdressed (during each production year) rates of P (0, 7, 15, 29, or 59 kg/ha)were applied to alfalfa established in two experiments in fall of 1988 and 1989. At each harvest in 1989 and 1990, mean stage by weight (MSW) was determined and forage samples were taken for neutral detergent fiber (NDF) and in vitro true digestibility (IVTD) analysis. In the 0‐ to 15‐cm soil layer, soil P concentrations averaged 6, 11, and 22 mg/kg of dry soil with 0, 29, and 59 kg P, respectively, incorporated. Soil P was not changed in the 15‐ to 30‐cm soil layer. Alfalfa herbage increased in P concentration with increasing P fertility level at some, but not all, harvests analyzed. Alfalfa maturity at harvest and NDF concentration increased with increasing P fertilizer rate, whereas IVTD decreased. Differences among treatments in NDF and IVTD probably were due to differences in plant maturity.     

Chlorophyll meter predicts nitrogen status of tall fescue

The nitrogen (N) status of a crop can be used to predict yield and supplemental N fertilizer requirements, and rapid techniques for evaluating the N status of crops are needed. A study was conducted to determine the feasibility of using a hand held chlorophyll meter (SPAD 502, Minolta Co. Ltd., Japan) to monitor N status of tall fescue (Festuca arundinacea Schreb.). Four diverse tall fescue genotypes were grown at three locations in Alabama and fertilized at four N‐rates from 0 to 336 kg ha^‐1. A similar experiment was conducted in the greenhouse using soil from the same field sites. Chlorophyll meter readings (SPAD) were taken, and extractable chlorophyll content, tissue N concentration and dry matter yield were determined at harvest. SPAD, extractable chlorophyll content, tissue N concentration, and dry matter yield increased quadratically (0.67 < R² < 0.99) with increasing N fertilization in both experiments. All genotypes responded similarly to applied N, with some differences in magnitude. Relationships between SPAD meter readings and extractable chlorophyll and tissue N concentrations were linear with r² > 0.95. An additional independent variable, the square root of the inverse of SPAD, lowered the residual mean square by 11 and 16%, respectively, for tissue‐N and chlorophyll concentrations, but did not increase the R². This would be preferred for predictive purposes. Tissue N concentrations at higher N‐rates were sufficient for maximum yield which occurred at 290 and 248 kg N ha^‐1 for greenhouse and field, respectively, but were lower than previously reported sufficiency values. The chlorophyll meter is an easy and efficient method of detecting tall fescue N status.     

Influence of surfactants on potassium uptake and yield response of cotton to foliar potassium nitrate

Foliar potassium (K) applications are intended to supplement soil K uptake, and thereby, increase cotton (Gossypium hirsutum L.) yields. Considerable research has been conducted to evaluate yield response to foliar K, but research evaluating surfactant effects on foliar uptake has been limited. Research was initiated in West Tennessee in 1991 to evaluate effects of foliar applied potassium nitrate (KNO₃) with and without surfactants on leaf and petiole K concentrations and on lint yield. Field research was conducted on three sites over a four year period using upland cotton ‘DPL 50’. Treatments included a check (no foliar treatment), 4.1 kg K/ha in water, 4.1 kg K/ha with Penetrator Plus, 4.1 kg K/ha with X‐77, 2.0 kg K/ha with Penetrator Plus, and 2.0 kg K/ha with X‐77. Surfactants were added to KNO₃ solutions at 1.25% v/v for Penetrator Plus and 0.5% v/v for X‐77. Kinetic was substituted for X‐77 after 1991 and was applied at 0.12% v/v. Cotton leaves and petioles were collected one, three, and seven days after each foliar application for K concentration determinations. Applying 4.1 kg K/ha (high‐K rate) as KNO₃ in water increased four‐year average leaf K but not petiole K concentrations in tissue collected 24 h after treatment relative to the check. Applying the high‐K rate with a surfactant increased the four‐year average concentration of leaves and petioles collected one, three, and seven days after application relative to the check or to the high‐K rate applied with water. Increases in both leaf and petiole K concentrations varied with year, with significant increases in two of the four years of the study. Yearly K concentrations of the day‐one and day‐three petioles were higher after applying the high‐K rate with Penetrator Plus relative to the check. Petiole K was not increased by applying low‐K rates with surfactants or the high‐K rate in water. First harvest lint yields were generally unaffected by foliar treatments. Second harvest and total yields were increased by applying the high‐K rate with Penetrator Plus relative to the other treatments. Yield responses may have been due in part to the nitrate anion (NO₃‐) being applied with the K+ cation, but higher K concentrations generally accompanied higher yields. These results suggest that surfactants may enhance K uptake and yield, but that more research is needed to determine why responses vary from year to year.     

Influence of high rates of topdressed KCl and K2SO4 on recovery of K,Cl, and SO4‐S by alfalfa and residual amount remaining in the soil

Abstract

This study was conducted to ascertain the percent of available K, Cl, and SO₄‐S recovered by alfalfa (Medicago sativa L. cv. ‘Vernal') herbage when various rates of K as KCl and K₂SO₄ were topdressed and also to determine where residual K, Cl, and SO₄‐S accumulated in the soil profile. An established stand of alfalfa growing on low fertility silt loam soil was topdressed in the spring of each of two harvest years with 0, 448, 896, 1344, and 1792 kg/ha of K as KCl or K₂SO₄. Four harvests were taken during each harvest year (1972 and 1973). Soil samples were taken during the autumn of 1973 to a depth of 91.4 cm in KCl‐fertilized plots, and to a depth of 76.2 cm in K₂SO₄‐fertilized and control plots.

Potassium recovery by alfalfa during two harvest years where K as KCl was applied at 448, 896, 1344, and 1792 kg/ha/yr was 56, 33, 20, and 17%, respectively. Recovery of available Cl from those same treatments was 30, 17, 12, and 10%, respectively. Where K as K₂SO₄ was applied at 448, 896, 1344, and 1792 kg/ha/yr, 55, 35, 27, and 22%, respectively, of available K was recovered. Recovery of available SO₄‐S from those same treatments was 16, 9, 7, and 5%, respectively. At the end of two years, a majority of the residual K was in the top 15.2 cm of soil. Residual Cl and SO₄‐S were concentrated at a depth of 30.5 to 76.2 cm in the soil profile.     

Effect of foliar and soil applied zinc on soil test levels,herbage composition,and yields of alfalfa

Abstract

Forages in the Northeast generally do not contain enough Zn to meet the National Research Council (NRC) recommended allowance for dairy cattle (40 mg/kg Zn). A study was undertaken to determine if foliar or soil application of Zn could increase Zn levels in alfalfa herbage to the NRC recommended allowance.

Alfalfa was treated with Zn by foliar applications of 0.34 and 0.68 kg/ha and soil application of 4.07 kg/ha. An untreated check was also included in the study. Average herbage Zn levels were 33.1 and 50.1 mg/kg for the low and high foliar applications, respectively. These levels were significantly higher than that of the check, 18.9 kg/ha. Average herbage Zn levels for the soil applied Zn treatment was 23.4 mg/kg. This level was also significantly higher than that of the check.

Although foliar Zn application significantly raised herbage Zn levels above those of the check, the results were erratic. The 40 mg/kg level was reached only one‐third of the time with the 0.34 kg/ha foliar application and two‐thirds of the time with the 0.68 kg/ha foliar application. Due to lower yields in comparison with cut 1, foliar application was more effective in raising herbage Zn levels in cuts 2 and 3. Foliar application of Zn does not appear to be a reliable means of insuring adequate herbage Zn levels for dairy cattle.     

Yield of alfalfa as influenced by levels of P and K fertilization

Abstract

This study was conducted to ascertain further the need for P and K fertilizers to obtain maximum herbage yields from alfalfa (Medicago sativa L.). Vernal alfalfa was established on a low K Piano silt loam (Typic Argiudoll) soil and topdressed with zero, 22.4, and 44.8 kg/ha of P in autumn of seeding year and with zero, 224, and 672 kg/ha of K as KC1 each autumn. The harvest schedule was three cuts annually at first flower; a schedule widely recommended in the North Lake states. No statistical significance was found for P levels nor for the P x K interaction; significance was found only for K levels. Maximum herbage yield was obtained with 224 kg/ha of K in the first harvest year, but with the 672 kg/ha of K rate in the second harvest year. Herbage K and Cl percentages and amounts removed from the soil increased significantly each year with each increase in K applied. Herbage P and N percentages were decreased significantly with the first increment of K. Residual herbage yields showed dramatically the influence of K fertilization on winter survival. All alfalfa stands with no K fertilization were killed completely. Residual yields and stands increased with each increase in K applied. Yield increase over the control was significant only with the second increment of K, while stands increased significantly with each increase in K applied. These data continue to confirm that high levels of soil K are needed for stand survival as well as for high herbage yields.     

Chlorine concentrations in alfalfa herbage and soil with KCl topdressing of a low fertility silt loam soil

Abstract

The purpose of this study was to determine the amount of Cl in plants and soil following topdressing of alfalfa with increasing amounts of KCl (0–0–60). The study was conducted with Ranger alfalfa on a low K Piano silt loam soil that had been topdressed twice during three years with a total of zero, 203, 406, 1220, and 2034 kg/ha of Cl as KCl (0, 224, 448, 1334, and 2240 kg/ha of K). Herbage was harvested annually three times at first flower plus an early October cut (4 cuts). The 3‐year average herbage yields were highest with 1220 kg/ha of topdressed Cl. Herbage yields decreased with 2034 kg/ha of Cl, but not significantly below that at 1220 kg/ha. Weakened and yellowed plants were noted in the spring of the second harvest year after 2034 kg/ha of Cl had been applied, and the first‐flower herbage contained 1.90% Cl. It was concluded that the weakened condition of the alfalfa was due to excess Cl.

Movement of Cl through the silt loam soil was rapid. The largest concentrations of Cl in the soil two years after the last KCl application were at the 76 to 91‐cm soil depth, the deepest soil sample tested.     

Phosphorus source effects on alfalfa yield,total nitrogen content,and soil test phosphorus

Abstract

Recent studies showing a lack of response by alfalfa (Medicago sativa L.) to phosphorus (P) fertilization have raised concerns about the efficacy of commonly used P fertilizer materials in the southwestern United States. Studies were conducted between 1982 and 1985 in southeastern New Mexico to evaluate (i) alfalfa yield response to different P sources, (ii) the effect of P fertilizer source on forage total nitrogen (N) content and leafiness, and (iii) the effect of P fertilizer source on soil test P. Nine P sources were applied annually from 1982 through 1984 at a rate of 58 kg P/ha. Alfalfa was grown during 1985 without fertilization to examine the residual effect of P sources. Triple superphosphate (TSP) and monoammonium phosphate (MAP) gave the highest alfalfa forage yields over the 3‐year application period, but no residual fertilizer effects were observed when fertilization was discontinued. Fertilization did not affect forage leafiness. Except for a small N response in forage total N content in 1984, neither P nor concomitant applied N had a significant effect on forage N content over the 3‐year period. Phosphorus fertilization significantly increased average soil test P for the 3‐year period, but there were no significant differences between treatments. Currently used P materials (TSP and MAP) still appear to be the most efficacious for alfalfa production.     

Effectiveness of different sources of manganese foliar sprays in alleviating manganese deficiency of Lupinus angustifolius L. grown on manganese deficient soils in western Australia

Responses of narrow‐leafed sweet lupins (Lupinus angustifolius L.) to foliar sprays of different sources of manganese (Mn) were compared in field experiments in three years at six sites in Western Australia. The relative effectiveness of manganese chelate (EDTA; 14% Mn) and manganese sulfate (25% Mn) applied as foliar sprays for alleviating Mn deficiency of lupins was assessed. Each source was sprayed at six levels of Mn (0, 0.125, 0.250, 0.50, 1.0, and 2 kg Mn/ha) when pods on the main stem were 2–3 cm long to define the relationship between seed and the amount of foliar Mn applied for lupins grown on Mn‐deficient soil. Manganese chelate, manganese sulfate, and the Mangasol sprays were equally effective. For all sources, 1.0 kg Mn/ha sprayed on the foliage was required to produce maximum seed yield and reduce split seed to an acceptable level (<4%). In all years, manganese sulfate banded with the seed produced similar seed yields as Mn sprayed on the foliage.     

Effect of potassium and boron upon yield and nutrient concentration of alfalfa

An alfalfa experiment was conducted to determine the effect of rates of K applied in the fall and rates of K applied, one‐half in the fall and one‐half after first harvest, upon yield and chemical composition. Three rates of B applied in the fall and also one‐half in the fall and one‐half after first harvest at the highest K rate (560 kg/ha) were also included. Herbage samples were taken from each plot at each harvest and analyzed for N, P, K, Ca, Mg, B, Cu, Fe, Mn and Zn. Significant effects of fertility upon yield and nutrient content were observed. Harvest x fertility interactions also affected many parameters. The Cu concentration of herbage was relatively uniform and not significantly affected by any factors studied.     

Potassium fertilization effects on yield and longevity of established alfalfa

Abstract

Limited information is available which describes the response of established alfalfa (Medicago sativa L.) to topdressing applications of K fertilizer in the Southeastern United States. Field experiments were conducted for three years to determine alfalfa response to rates and time of K application. The experiments were established in two‐year old stands of alfalfa on a Decatur silty clay loam (clayey, kaolinitic, thermic Rhodic Paleudults) and a Hartsells fine sandy loam (fine loamy, siliceous, thermic Typic Hapludults) located in northern Alabama. Potassium as KCl was broadcast in the spring prior to regrowth. For split application treatments, the K was applied in early spring and after the second cutting. Annual total K rates ranged from 56 to 596 kg/ha. Potassium fertilization maintained alfalfa stand density on both soils, but the experiment on the Decatur soil was discontinued after two years due to severe stand loss when the lowest rate of added K was used. Alfalfa yields were increased by the application of K and maximum yields occurred when K was applied according to soil test recommendations made by the Auburn University soil testing laboratory. Potassium applications increased the concentration of K, decreased the concentration of Ca and Mg and had little effect on the concentration of N in tissue from the two cuttings sampled. The split application of K did not consistently increase forage production. There was little movement of K below 25 cm in either soil when K rates of 56 to 596 kg/ha/yr were repeated yearly for up to three years.     

Effects of liming on yield,forage cation composition,and tetany potential of wheat in Kansas

Abstract

We studied the effects of liming on dry matter production, nutrient composition, and grain yields of wheat in field experiments conducted on two soil types at three locations during the 1976–77 and 1977–78 growing seasons. Lime sources were commercial agricultural lime, finely divided stack dust, and dolomitic limestone (which contained 10.6% Mg). Lime applied at 2,800 kg/ha in the 1976–77 and 10,750 kg/ha in the 1977–78 experiments provided Mg from the dolomite at rates of 300 and 1,140 kg/ha, respectively.

Soil pH was significantly increased by liming, but Mg saturation percentages were significantly greater only at the 1,140 kg/ha rate. Forage dry matter and grain yields were not increased by lime applied at the lower rate, but significant increases were found in dry‐matter production in the late fall and spring samplings of the 1977–78 experiment. Those increases in plant growth and dry matter production were probably due to reductions in the soluble Mn and Al concentrations in the soil. Forage N and P concentrations were generally not influenced by liming. Potassium concentrations in forage from the limed plots were usually equal to or greater than those in forage from unlimed plots. Calcitic limestone sources generally increased forage Ca concentrations, but liming with dolomite more often than not depressed Ca concentrations below levels found in the check plots. Dolomite, when applied at the 1,140 kg/ha rate, effectively increased the forage Mg concentration, although the concentration exceeded 0.2% only during the early growth stages. Liming generally showed no significant reduction in the tetany potential of the wheat forage as predicted by the equivalent ratio K/(Ca + Mg).     

Interactions of gamma‐irradiated sewage,nitrogen and phosphorus for Sorghum on a calcareous soil

Abstract

The interaction of gamma‐irradiated sewage sludge, nitrogen and phosphorus fertilizers on dry matter production, phosphorus concentration and phosphorus uptake of sorghum was examined. Three crops of sorghum were grown in the greenhouse in 19 1 plastic buckets. The phosphorus and sludge treatments were applied at the initiation of the experiment only. Nitrogen was applied to the corresponding nitrogen treatment pots before each of the three croppings.

There was a significant nitrogen x sewage interaction for dry matter production, phosphorus concentration and phosphorus uptake in each harvest. There was a significant phosphorus sewage sludge interaction in the first harvest for phosphorus uptake. All other possible interactions were not statistically significant. The 67 metric ton/ha sludge rate produced nearly the same yield as the nitrogen treatment. In the first harvest, sludge significantly increased plant phosphorus uptake from the fertilizer phosphorus. The phosphorus uptake in sorghum from 472 and 944 kg P/ha from the sludge treatments was comparable to that from 1299 and 2598 kg P/ha from triple superphosphate.     

Use of an N-tester chlorophyll meter to tune a late third nitrogen application to wheat under humid Mediterranean conditions

In Northern Spain, winter wheat is usually fertilized with 180–220 kg N/ha split in two applications. To reduce this rate, a strategy was tested which comprised three nitrogen (N)-applications, the latter being tuned to the nutritional needs of the crop using a chlorophyll meter. N-fertilization experiments were performed on winter wheat (Soissons variety). Treatments consisted of three N-broadcasts of 40, 60, and either 0, 40, 60, or 80 kg N/ha respectively applied at Zadoks scale growth stages 21, 30, and 37. An over-fertilized treatment of 220 kg N/ha was included for normalization of chlorophyll-meter values. Chlorophyll-meter readings were performed at growth stage 37, before fertilization. When normalized chlorophyll-meter values were below 92%, yield and grain protein contents attained with 40+60+0 kg N/ha could be respectively enhanced with third applications of 60 or 80 kg N/ha and 40 kg N/ha.     

Effect of manganese and soil pH on the iron content of crops grown on podzol soils

In a greenhouse study on three podzol soils with pH values of 5.4–5.6, liming to pH 7.6 or higher decreased the Fe concentration of pea plant tissues from 47 to 42 ppm. In the case of barley, liming the soil increased the mean tissue Fe concentration from 104 to 119 ppm at pH 7.6 and to 107 ppm at pH 7.7. Field experiments on wheat, oats, alfalfa, and timothy showed that Mn applied to the soil or as foliar spray did not affect the Fe concentration of cereal or forage plant tissues. Liming did not affect the Fe concentration of cereal kernels but on a few locations it increased the Fe concentration of the boot stage tissue. The Fe concentration in oats was higher than that in wheat. Based on the results of a survey, it was found that forage legumes contained more Fe than did timothy. The survey also showed that a few Fe values in timothy and cereals would be considered low, although Fe deficiency has not been experienced in this region. A number of the samples would be in the deficiency range from the animal nutrition standpoint.     

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.     

水、磷对紫花苜蓿产量及水肥利用效率的影响

【目的】紫花苜蓿作为畜牧业生产中最主要的优质绿色饲料,是发展草食畜牧业的物质基础,同时它也是一种需水需肥较多的作物。如何从技术方面提高单位面积苜蓿产量,实现苜蓿高产栽培是科学研究人员及生产者研究的重点。北京市东南部接壤的蓟县、宝坻及南部接壤的廊坊、武清等地区,是北京市在生态和环境优先发展原则下畜牧养殖业外移的重要承接区域,苜蓿在当地种植缺乏科学指导,年干重产量仅为7500~10000 kg/hm2,盐碱地年产量更低,为4500~6000 kg/hm2。本研究通过苜蓿水肥试验确立紫花苜蓿达到高产的最佳磷肥施用水平和灌水量,为京南地区苜蓿高产及水肥的高效利用提供可借鉴的水肥管理技术。【方法】实验在低磷砂壤土条件下进行,选用紫花苜蓿中苜2号品种,设置全生育期不灌水（W0）、以及返青后及第1、2茬刈割后灌水且每次灌水25 mm （W1）、50 mm （W2）、75 mm （W3）4个灌水处理;每个灌水处理下设置不施磷（F0）、施P2O5 105 kg/hm2（F1）、210 kg/hm2（F2）3个施磷量处理,研究了灌水和施磷对紫花苜蓿产量、水分和磷肥利用效率的影响。【结果】1）灌水对1、2茬苜蓿产量的影响有显著差异,对3、4茬及全年产量的影响无显著差异;施磷肥对第3茬苜蓿产量没有显著影响,但对第1、2、4茬及全年苜蓿产量的影响均存在显著差异。2）灌水和施磷肥对紫花苜蓿的水分和肥料利用效率均有显著影响,随着施磷量的增加,苜蓿的水分利用率逐渐增大,说明施磷可以提高水分利用效率;随着灌水量的增加,苜蓿的磷肥利用效率呈先增加后降低的趋势,说明适当的增加灌水量可以提高苜蓿的磷肥利用效率。【结论】综合考虑紫花苜蓿产量、水分和肥料利用效率等指标,最优试验处理为每次灌水量50 mm,施P2O5 210 kg/hm2,其次为每次灌水量25 mm, 施P2O5 210 kg/hm2。     

Effect of B,Mn and Zn on nodulation and N2‐fixation in southernpeas

Abstract

Two greenhouse studies were conducted to evaluate the effect of B, Mn and Zn on nodulation and N₂‐fixation of southernpea (Vigna unguiculata (L.) Halp.) cultivars ‘Freezegreen’, ‘Mississippi Silver’ and ‘Pinkeye Purple Hull’. The cultivars were grown in plastic pots with a Norfolk sandy loam (fine, loamy siliceous thermic, Typic Paleudult) soil treated with B, Mn and Zn at rates of 0, 5, 10 and 20 kg/ha each at pH levels 5.5, 6.0 and 6.5. At pH 6.5 all micronutrient treatments significantly increased nodulation and N₂‐fixation over the control (no micronutrient applied). The effects of B, Mn and Zn on nodulation and N₂‐fixation depended on the cultivar and soil pH. For plants given the 5 kg/ha B and Mn treatments, ‘Mississippi Silver’ produced the highest number of nodules and ‘Pinkeye Purple Hull’ the least. At 20 kg/ha Zn, nodulation of ‘Freezegreen’ was highest and ‘Pinkeye Purple Hull’ the lowest. As a whole, maximum nodulation was at 5 kg/ha B and Mn and 20 kg/ha for Zn. Nitrogen fixation rates responded similarly except that the optimum rate for Zn was 10 kg/ha. Seed yield of plants peaked at 5 kg/ha for B and 10 kg/ha for Zn, indicating a possible relation of N₂‐fixation to seed yield.     

Determination of cotton nitrogen status with a handheld chlorophyll meter

The ability of a hand‐held chlorophyll meter (SPAD‐502 Chlorophyll Meter³, Minolta Camera Co., Ltd., Japan) to determine the N status of cotton (Gossypium hirsutum L.) was studied at field sites in Alabama and Missouri. Meter readings on the uppermost fully‐expanded leaf were compared to leaf‐blade N and petiole NO₃‐N at first square, first bloom and midbloom as to their seed cotton yield predictive capability. Nitrogen was applied at rates of 0, 45, 90, 135, 180 and 225 kg ha^‐1 to establish a range of cotton chlorophyll levels, tissue N concentrations, and seed cotton yields. A typical curvilinear cotton yield response to N fertilizer was observed in Alabama experiments.

Because of adverse weather conditions, cotton yield in Missouri experiments did not respond to N. Chlorophyll meter readings were significantly correlated to leaf‐blade N concentration at all three stages of growth for all experiments. In Alabama, chlorophyll meter readings compared favorably to leaf‐blade N and petiole NO₃‐N with respect to their seed cotton yield predictive capability at all three stages of growth. It appears that hand‐held chlorophyll meters would be as reliable as leaf‐blade N and petiole NO₃‐N for predicting supplemental N fertilization requirements of cotton. However, more research will be required prior to use of chlorophyll meter readings for routine cotton‐N recommendation purposes.     

Chlorophyll meter as nitrogen management tool in malting barley

Abstract

Variable precipitation in many regions makes it difficult to predict yield goals and nitrogen (N) rates for malting grade barley (Hordeum vulgare L.). During years with below normal growing season precipitation, barley fertilized at the recommended rate often exhibits grain protein concentrations exceeding what is acceptable for malting. A study was conducted to evaluate the chlorophyll meter as a N management tool. Barley was grown under several N rates in the field. Chlorophyll meter readings and N additions were made at the Haun 4 to 5 growth stage, and grain yield and protein concentrations were evaluated at maturity. Chlorophyll meter readings, normalized as meter reading from treatment plot divided by that from a plot receiving a full N treatment at the Haun 4 to 5 growth stage, were correlated with grain yield (r²=0.67). Stands having normalized chlorophyll meter readings below 95% responded to N additions with yields equivalent to the fully fertilized stand and grain protein concentrations acceptable for malting. A N management strategy is proposed whereby 40 to 50% of the N calculated for the yield goal is applied at planting and a fully fertilized reference strip is included for each variety or soil type. At the Haun 4 to 5 growth stage, chlorophyll meter readings are taken in the reference strip and in the field. Normalized chlorophyll meter readings below 95% of the reference strip indicate a need for additional N fertilizer. This strategy will provide producers with additional time (up to a month) to evaluate growing season conditions before investing in additional crop inputs and will improve the likelihood that a barley crop acceptable for malting will be produced.