Potassium concentration in leaf‐blades and petioles as affected by potassium fertilization and stage of maturity of cotton

Abstract

Analysis of data obtained from samples collected in the Delta area of Mississippi showed that the potassium concentration of young mature and old mature cotton leaf‐blades correlated better with soil test potassium than did that of the apical immature leaf‐blades.

Results from field studies indicated that the old mature petiole was the most sensitive indicator of the potassium status of the cotton plants. The potassium concentration in both leaf‐blades and petioles decreased with stage of maturity from early square to early half‐grown boll. Potassium concentration did not fluctuate with sampling at different times of the day. The rate of decline of potassium concentration was greater in petioles of mature cotton leaves than in the leaf‐blades. For mature leaves, the potassium concentration of leaf‐blades was highly correlated with that in petioles, but for immature leaves, the correlation was poor. The rate of decline of potassium concentration in both cotton leaf‐blades and petioles was not affected by potassium fertilization but was a function of maturity stage.     

Dry matter yield and nitrogen recovery from bromegrass in south‐central Alberta as affected by rate of long‐term nitrogen applications

Abstract

A field experiment was conducted on a Thin Black Chemozemic soil at Crossfield in south‐central Alberta to determine the effect of long‐term application of ammonium nitrate on dry matter yield (DMY), protein yield (PY), protein concentration, N use efficiency and recovery of N applied to bromegrass (Bromus inermis Leyss.) grown for hay. The N fertilizer was applied at 0, 56, 112, 168, 224, 280, and 336 kg N/ha in early spring of every year from 1968 to 1986. The DMY increased with applied N achieving a maximum at 224 kg N/ha, though the rate of increase in DMY from N fertilization was greatest with the first two increments applied (i.e. 56 and 112 kg N/ha). Protein yield and protein concentration maximized at 336 kg N/ha. The DMY was greater with a single‐cut system than with a double‐cut system. The DMY varied from year to year, but it was not closely related to precipitation received during the April to August period (R² = 0.37). However, in some years low DMYs were associated with low precipitation, or a lack of timeliness of rainfall, or a combination of both. The N use efficiency and % N recovery in bromegrass decreased with increasing N rate. The maximum DMY calculated from quadratic regressions ranged from 3.16 t/ha to 7.91 t/ha, and maximum N rate ranged from 205 to 258 kg N/ha. In summary, DMY, PY, and protein concentration increased, and N use efficiency and % N recovery decreased with increasing N rate in this 19‐year study.     

A re‐examination of exchangeable acidity as extracted by potassium chloride and potassium fluoride

Abstract

In order to better understand some of the factors likely to affect measurements of KC1 extractable acidity, experiments were conducted using synthetic solutions and extracts from a wide range of contrasting soils. The reagents used for measuring exchangeable acidity (i.e., KC1 and KF) were also examined to evaluate the effects of chemical impurities on acidity measurements. Two commonly used titrimetric methods were adapted and tested to determine the accuracy and precision of acidity measurements. The exchangeable acidity of soil extracts was investigated by extraction methods, extractant concentration, and extractant volume. Results from the soil extract experiments indicated that continuous shaking has no significant effect on acidity measurements. Filtration, however, is critical, especially for acidic organic‐rich soils, since aluminum (Al) ions can be lost during centrifugation. Extractant concentration and volume had variable effects on the acidity measurements for individual soils. In general, the modified Yuan's method is preferable to the modified Thomas’ method for estimating exchangeable Al. To ensure successful determination of exchangeable acidity, we recommend using a wider KCl:soil ratio (>15:1, v/w) for organic soils with low base saturation and allophanic Andisols. In sum, potassium chloride and potassium fluoride extraction for estimating exchangeable acidity is applicable for most soils.     

Variation of early growth and nutrient content of no‐till corn and soybean in relation to soil phosphorus and potassium supplies

Abstract

Knowledge of relationships between variation in early plant growth and soil nutrient supply is needed for effective site‐specific management of no‐till fields. This study assessed relationships between soil test phosphorus (STP) and potassium (STK) with early plant growth and P or K content of young corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] plants in eight no‐till fields. Composite soil (0–15 cm depth) and plant (V5‐V6 growth stages) samples were collected from 400‐m² areas at the center of 0.14‐ha cells of a 16‐cell square grid and from 2‐m² areas spaced 3 m along each of two 150‐m intersecting transects. Correlation, regression, multivariate factor analyses were used to study the relationships between the variables. Variability was higher for samples collected from the transects. Plant dry weight (DW), P uptake (PU), and K uptake (KU) usually were correlated with STP and STK but the correlations varied markedly among fields. Relationships between soil and plant variables could not always be explained by known nutrient sufficiency levels for grain production. Plant P concentration (PC) was not always correlated with STP and sometimes it increased linearly with STP, but other times increased curvilinearly until a maximum was reached. Plant K concentration (KC) usually was correlated with STK, however, and increased linearly with increasing STK even in fields with above‐optimum STK. The results suggest greater susceptibility of early growth to STP than to STK and greater plant capacity to accumulate K compared with P over a wide range of soil nutrient supplies. Variation in STK likely is a major direct cause of variation in KC over a wide range of conditions but variation in STP is not likely a major direct cause of variation in PC when high STP predominates.     

Tomato response to long‐term potassium and lime application on a sandy ultisol high in non‐exchangeable potassium

In a ten‐year study of potassium (K) and lime application to a Kalmia sandy loam (fine‐loamy, siliceous, thermic Typic Hapludult), a soil high in nonexchangeable K, corn (Zea mays L.) and soybean [Glycine max (L.) Herr.] have not responded to applied K. The objectives of this study were to determine if a high K‐requiring crop such as tomato (Lycocersicon esculentum Mill. cv. Redpak) would respond to KCl fertilizer rate or lime type (dolomitic, calcitic, and mixed) and rate on such a soil. Potassium was applied at 0, 56, and 112 kg K/ha every year for ten years. Lime was applied at 0, 2, and 9 Mg/ha in calcitic, mixed, and dolomitic forms twice in ten years (1970 and 1973). In 1980, the tenth year of the study, tomato fruit was harvested by hand once‐over to simulate machine harvest and divided into four maturity groups by color. Soil pH was higher with dolomitic than calcitic lime. Soil K saturation was not influenced by lime rate or type. Fruit yield and leaf phosphorus (P), calcium (Ca), and magnesium (Mg) concentrations increased with increasing lime rates. Leaf K, manganese (Mn), iron (Fe), boron (B), copper (Cu), zinc (Zn), barium (Ba), strontium (Sr), and aluminum (Al) concentrations decreased with increasing lime rate. Leaf Mn, Ba, and Sr concentrations were lower with dolomitic than with calcitic lime. Lime type had no effect on tomato yield. Wide ranges in basic cation saturation ratios had little effect on yield. Soil K saturation and leaf K, Zn, and Ba concentrations increased with increasing K rate. Soil Ca and leaf Ca, Mg, and Al concentrations decreased with increasing K rate. Applied K had no effect on total yield but onceover marketable yield increased linearly with increasing K rate. Marketable yield increased 14% with an increase in K rate from 0 to 56 kg/ha. Thus, fruit maturity was apparently hastened by K fertilization.     

Soil chemical properties after long‐term n fertilization of bromegrass: Nitrogen rate

Abstract

Nitrogen (N) fertilizers increase yield and quality of grass forage, and may also alter soil chemical properties. A field experiment was conducted in south‐central Alberta to determine the effect of long‐term application of ammonium nitrate to bromegrass on concentration and downward mobility of soluble NO₃‐N, extractable NH₄‐N, P, Ca, Mg, and K, and total C and N in a Thin Black Chernozemic loam soil. The fertilizer was applied annually in early spring for 16 years at 0 to 336 kg N/ha. There was little accumulation of NO₃‐N in the soil at N rates of 112 kg/ha or less. However, at rates higher than 112 kg N/ha there was accumulation of NO₃‐N in the 15–30 and 30–60 cm layers, but very little in the 90–120 cm depth. The NH₄‐N accumulated in the 0–5 cm layer when the fertilizer was applied at rates between 168 to 280 kg N/ha and in the 5–10 cm layer at N rates exceeding 280 kg/ha. There was a decline in extractable P in soil with N application up to 84 kg N/ha rate, while it increased with high N rates. The increasing amounts of applied N resulted in a decline in extractable soil Ca, Mg and K, and this decrease was more pronounced in the 0–5,5–10,10–15, and 15–30 cm layers for K, 0–5 and 5–10 cm layers for Ca, and 0–5, 5–10, and 10–15 cm layers for Mg. There was a build‐up of total C and N in the surface soil with increasing rate of applied N.     

Phosphorus sorption by four soils receiving long‐term applications of fertilizer

Abstract

A laboratory study was conducted to evaluate P sorption in the Ap horizon of four soil series in the Ultisol order (Benndale Is, Hartsells fsl, Lucedale fsl, and Dewey sicl) receiving the same fertility treatments since 1929. Soil was collected in the spring of 1985 from 4 treatments: i) no‐lime, plus P (total fertilizer P = 1584 kg/ha from 1929 to 1985); ii) no‐K, plus P (total fertilizer P = 1584 kg/ha); iii) low‐P (total fertilizer P = 442 kg/ha); 4) standard treatment (total fertilizer P = 2376 kg/ha). The soils and treatments within a soil varied in pH, total P, Mehlich 1 extractable P, K, Ca and Mg, and KC1 extractable Al. The four soils had large differences in P sorption capacity which increased with increasing clay content. The Dewey (27 % clay) soil had the highest P sorption capacity and the Benndale (4 % clay) soil had the smallest P sorption capacity. Sorption of P within a soil was affected by the rate of added P and past fertility treatment. Treatment differences in P sorption were due primarily to the level of extractable P and soil pH. Within a given soil, P sorption (at a given rate of added P) generally decreased as the level of extractable P increased. Regression analysis of P sorption data for equilibrium P concentrations of 1 to 32 μmol/L showed that the parti‐ tioning between sorbed and solution P (buffer power) had not been changed by 56 years of annual applications of P. The maximum P sorption capacity of the four soils was decreased slightly by P fertilization.     

Mycorrhizal colonization and nutrition of wheat and sweet corn grown in manure‐treated and untreated topsoil and subsoil

Dry bean yields (Phaseolus vulgaris L.) were raised to similar levels as the topsoil by manure application to eroded or leveled Portneuf silt loam soil (coarse‐silty mixed mesic Durixerollic Calciorthid). Only soil organic matter and zinc (Zn) content of leaf tissue were correlated with improved yields. Manure application increased mycorrhizal colonization and Zn uptake in pot experiments with dry bean which would explain the increased yields in the field. A field study was conducted to see if similar effects of manure and mycorrhizal colonization could be observed in field grown spring wheat (Triticum aestivum L.) and sweet corn (Zea mays L.). This study was conducted on existing experiments established in the spring of 1991 at the USDA‐ARS farm in Kimberly, Idaho, to study crop rotation/organic matter amendment treatments on exposed subsoils and focused on mycorrhizal colonization as related to topsoils and subsoils treated with conventional fertilizer (untreated) or dairy manure. Mycorrhizal root colonization was higher with untreated than with manure‐treated wheat and sweet corn. Root colonization was also higher in subsoil than in topsoil for wheat, but there were no differences between soils for sweet corn. Shoot Zn and manganese (Mn) concentrations generally increased with increased root colonization for both species (except between soils with corn Mn contents). Wheat shoot potassium (K) concentration was increased by manure application, but the affect declined with time, was the opposite of colonization and was not observed with sweet com. Phosphorus (P), calcium (Ca), magnesium (Mg), iron (Fe), and copper (Cu) concentrations either were not influenced or were erratically affected by mycorrhizal colonization. Yields of wheat were highest for manure‐treated subsoil and topsoil compared to untreated soils. Mycorrhizal colonization was different between conventional and manure‐treated soils and between topsoil and subsoil and these differences increased Zn and Mn uptake, but they did not explain the improvement in wheat yields obtained with manure application.     

Evaluation of the growth and quality of the “Ife Plum” tomato as affected by boron and calcium fertilization

A local variety of tomato (Lycopersicon esculentum, Ife plum cv. 51691) was grown in soil culture for 5 months and treated with B at concentrations of 0, 1, 2, 4, 8, and 16 ppm as H₃BO₃, and Ca at 0, 40, 80, and 160 ppm as Ca(OH)₂. A significantly positive correlation was established between organic matter and water ‐ soluble B (r = 0.970), while the relationship between pH and B was negative (r = ‐0.490). Application of B at 2 ppm improved all growth parameters studied. Boron application higher than 2 ppm, induced leaf chlorosis and later necrosis of nodes and roots. Fruit yield correlated positively with soil ‐ B, stem diameter and floral number (r = 0.597, r = 0.650 and r = 0.812, respectively). Soil‐ and plant‐B were positively correlated (r = 0.790). Calcium when applied singly at higher levels increased total chlorophyll content of the leaf. Tomato fruit yield was optimum at B:Ca treatment concentration of 2 ppm B (4.48 kg/ha B) and 160 ppm Ca (358.4 kg/ha Ca), corresponding to a B:Ca fertilizer ratio of 1.80.     

Dynamics of maize straw–derived nitrogen in soil aggregates as affected by fertilization

Journal of Soils and Sediments - The addition of maize residue nitrogen (N) to the soil strongly influences soil N accumulations, but the specific contributions of maize residue N to soil...     

Soil organic carbon as affected by direct drilling and mulching in sugar beet – wheat rotations

The effect of conventional ploughing, mulching, and direct drilling on the soil organic C (soil C_org) contents through the soil profile and on total soil C_org stocks (0–45 cm) was investigated at five different German sites. All sites showed similar results: after 10–13 years, soil C_org contents in the surface soil (0–10 cm) were 15–71% and 33–42% higher under direct drilling and mulching, respectively, than under ploughing (8–18 g kg^?1). Under ploughing, the soil C_org contents were distributed homogenously through the soil profile. Either mulching or direct drilling resulted in 3–28% higher soil C_org stocks than ploughing (49–116 t ha^?1). However, the tillage management was no significant factor since the sites showed the effects to different extents but were the mathematical replications. Five to six years later, trends and values were similar. We concluded that the main effect of mulching or direct drilling was the stratification with higher soil C_org contents in the surface soil. Since this is a positive means for soil protection, we suggested that the use of mulching or direct drilling can contribute to a sustainable soil management in crop rotations with sugar beet which are characterized by a strong physical impact on the soil during harvest.     

Phytotoxicity of organic acids as influenced by montmorillonite,hydroxy‐Al montmorillonite and phosphate fertilization

Abstract

The germination and growth of wheat seedlings were studied at pH 5.5 in liquid growth media with organic acids in concentrations ranging from 800 to 1200 ppm, before and after interaction of the organic acids with montmorillonite and hydroxy‐Al montmorillonite. Germination was not affected by the organic acids, but subsequent growth was dependent on the kind and concentration of organic acid in the growth medium. Acetic acid was more inhibitory than citric acid. Gallic acid polymerized at pH 5.5 and was phytotoxic at 1200 ppm. Interaction of organic acids with montmorillonite and hydroxy‐Al montmorillonite reduced the concentration of organic acids in solution by adsorption. Despite this reduction in concentration the phytotoxicity of the growth media was enhanced after the interaction. This was caused by the dissolution of surface Al and the effect was more pronounced in cases where hydroxy‐Al interlayered montmorillonite was the adsorbent. Additions of P as KH₂PO₄ alleviated the phytotoxicity of organic acids but not the associated Al toxicity. The amount of P lost by adsorption or precipitation was dependent on the form of Al in the growth media.     

Seasonal sucrose,drymatter, and cation concentrations of sugarbeet as influenced by variety and N‐fertilization

Abstract

This study evaluated the effect of variety and nitrogen (N) fertilization on sucrose, dry‐matter, and cation concentrations in sugarbeet (Beta vulgaris L.) root tissue. A field experiment was conducted on a non‐saline, calcareous Nunn clay loam soil (Aridic argiustoll) using a factorial experimental design with three N‐rates, two varieties, and four replications. Beets were harvested nine times during the growing season. The first and final harvests were on June 25 and October 11, respectively. In addition to the above measurements, purity and extractable sucrose also were measured at the final harvest. Dry‐matter content, sucrose, sums of monovalent and divalent cations, and the monovalent:divalent cation ratios all were influenced significantly by variety, N‐fertilization, and date of harvest. Sucrose concentration was negatively correlated to the sum of monovalent and divalent cations. Root drymatter content was negatively correlated to the monovalent:divalent cation ratio. A relationship of cation concentration to the organic‐ and inorganic‐ anions that influence purity is discussed.     

Effects of long‐term nitrogen dioxide fumigation and nitrate supply on nitrite and Leghemoglobin concentrations,pH, and nitrogenase activity of soybean root nodules

Exposing 12‐day‐old soybean plants to 0.2 ppm nitrogen dioxide (NO₂) for four weeks increased the nitrite concentration and acidity, and decreased the Leghemoglobin (LHb) concentration and the nitrogenase activity of root nodules. The supply of 1 mol.m^‐3 nitrate to the roots intensified the nitrite accumulation, decreased the acidity of the nodules, and alleviated the inhibition of nitrogenase activity by NO₂ fumigation. These results suggested that the inhibition of nitrogen (N₂) fixation by N fertilizer supply might relate to the acid‐alkali balance in nodules.     

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

Abstract

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

Response of corn to plowed‐down and disked‐in Zn as zinc sulfate

Abstract

A field investigation was conducted to compare the efficacy of plowed‐down and disked‐in Zn as ZnSO₄.H₂O in correcting Zn deficiency of corn (Zea mays L.). The soil, Buchanan fine sandy loam, was nearneutral in pH and contained 0.7 ppm of EDTA‐extractable Zn and 1.4 ppm of dilute HCl‐H₂SO₄ extractable P. Application of 6.72 kg Zn/ha as ZnSO₄.H₂O corrected Zn deficiency of corn plants on the soil. Corn grain yields and Zn concentrations in tissue samples indicated that the plowed‐down and disked‐in Zn were about equally effective in correcting Zn deficiency where the level of Zn application was 6.72 kg/ha.     

Quantity‐intensity parameters of potassium in relation to uptake by guinea‐corn in representative soils of the ecological zones of Nigeria

Abstract

Quantity‐intensity (Q‐I) relation studies were often used to supplement information obtained from conventional soil tests for the estimation of potassium (K) needs of crops. With a view to ascertaining the reliability of the Q‐I relation parameters for comprehensive characterization of K dynamics in typical Nigerian soils, K values derived from Q‐I isotherms were related to neutral normal ammonium acetate (1 N NH₄OAc, pH 7.0) (exchangeable) K, other soil K forms [non‐exchangeable (K_ne), exchange (K_e), mineral K (K _m ), and solution K (K_s)] and the K uptake by Guinea‐corn (Sorghum bicolor, var. LS 187) subjected to weekly cuts in Neubauer cultivation vessels. Most of the soil K (about 98%) was in the form of soil minerals while less than 1% was plant available whereas about 1% was trapped within the interlattice layers of the clay minerals (as fixed K or K_ne). Mineral K (K_m) content was closely related to total K (K_t), but not to the other forms, K_ne, K_e, and K_s. A close relationship was noted between the two components of labile K (K_e and K_s). Except for % K saturation, the relationships between the K measurements with plant response were poor. The results of these investigations clearly demonstrate that the Q‐I relation could not adequately characterize the K dynamics of these tropical soils.     

Chemical fractionation,water solubility and temporal distribution of sheep faecal sulphur fractions in grazed pastures receiving long‐term sulphate fertilization

Abstract

Although over 40% of excretal S is returned to intensively sheep ‐grazed pastures as faecal S, limited information is available on faecal S fractions, their water solubility and temporal distribution. This study reports results obtained from sheep faeces returned to grazed pastures which have received long‐term annual sulphate applications for 15–20 years. Five freshly‐voided sheep faecal samples (<100 g moist faeces per sample) per sampling were randomly collected at approximately one month intervals over a one‐year growing season. Faeces were fractionated into total S, inorganic SO₄ ^2‐, ester SO₄ ^2‐, Hi‐reducible S and C‐bonded S. Results obtained showed that faecal total S, ester SO₄ ^2‐ Hi‐reducible S and C‐bonded S fractions varied significantly throughout the year. Carbon‐bonded S was the dominant (>80%) faecal S fraction, regardless of faecal total S content or the time of year faecal samples were deposited. Faecal ester SO₄ ^2‐ and inorganic _SO₄ ^2‐fractions accounted for 3.3–7.1% and 0.1–14% of faecal total S respectively. Thus approximately 3.4–21.1% of faecal total S was estimated to be potentially leached or readily available to pasture plants. The Hi‐reducible faecal S fraction was significantly‐correlated (r = 0.59***; *** = P ≤ 0.001) with HCl‐extractable faecal inorganic S, which was considered to represent faecal total SO₄ ^2‐ (ester SO₄ ^2‐ and inorganic SO₄ ^2‐ fractions).

The solubility of different faecal S fractions was determined by sequential extraction of ground (< 1 mm) faeces three times (30 minutes per extraction) with water or 0.01 M Ca(H₂PO₄)₂ solution (1: 5 ratio of faecal DM: extractant). Both amounts of water‐extractable and Ca(H₂PO₄)‐extractable faecal S fractions were found to vary significantly throughout the year. Ca(H₂PO₄)₂ tended to extract more inorganic faecal S than water, attributed to the presence of phosphate and the low pH (pH=4) of Ca(H₂PO₄)₂ extractant. A significant proportion (15–25%) of faecal S was extracted by water and most (70%) of this water‐extractable faecal S was in the organic S fraction. Water‐extractable inorganic faecal S probably originated from the faecal total SO₄ ^2‐ fraction as shown by their significant correlation (r = 0.45** ‐0.63***; ** = P≤ 0.01; *** = P≤ 0.001). Some of the faecal S in water extracts may also originate from the faecal C‐bonded S fraction, as a significant correlation was obtained between C‐bonded faecal S and either water‐extractable faecal organic S (r = 0.53–0.57***; *** = P ≤ 0.001) or water‐extractable faecal inorganic S (r = 0.40–0.41*; * = P ≤ 0.05).

Significant amounts of faecal inorganic SO₄ ^2‐ and ester SO₄ ^2‐ fractions were removed by Ca(H₂PO₄)₂ extractant. The Ca(H₂PO₄)₂‐extractable faecal inorganic S was significantly correlated (r = 0.73***^; *** = P ≤ 0.001) with water‐extractable faecal inorganic S.     

Forage yield and crude protein of interseeded legume‐bermudagrass mixtures as affected by phosphorus fertilizer 1

Bermudagrass (Cynodon dactylon L.) is a warm season perennial that is well adapted in the southern Great Plains. It is one of the region's most important forage crops used for livestock production, and is commonly grown without legume interseeding. Recent research has investigated ways of improving the quality and quantity of this forage. The objectives of this study were to determine the effect of interseeded legumes and phosphorus (P) fertilizer on bermudagrass pasture forage yield and crude protein content. One experiment was initiated in 1993 in eastern Oklahoma in an established bermudagrass pasture. Red clover (Trifolium pratense L.), ladino clover (Trifolium repens L.), and two varieties of alfalfa (Medicago sativah), ’alfagraze’ and'common’, were interseeded by hand into an established stand of bermudagrass. The effect of P on forage yield and crude protein was evaluated using a 30‐kg P ha^‐1 rate applied at establishment versus no applied P. Forage yield was collected three times throughout the growing season each year from 1994 through 1997. When both alfalfa varieties were interseeded into a bermudagrass pasture without applying additional P fertilizer, forage yields for the legume‐grass mixtures decreased below those obtained from the monoculture bermudagrass in the first year of the stand. The alfalfa variety ‘alfagraze’ interseeded into established bermudagrass decreased total forage yield over the entire 4‐yr study. Interseeded red clover and ladino clover increased crude protein of the forage compared with monoculture bermudagrass the first two years of the study, with red clover continuing to increase crude protein in the fourth year. However, when 30 kg P ha^‐1 was applied to the bermudagrass prior to establishment of the legumes, no change in yield or protein was observed for both alfalfa varieties’ interseeding treatments versus the unfertilized mixtures. Although forage yield may not be increased, interseeding legumes into established bermudagrass could provide an efficient way to improve pasture crude protein without the use of inorganic fertilizers. However, if alfalfa ('common’ or ‘alfagraze') is interseeded, additional P may need to be applied at legume establishment to prevent possible yield decreases.     

Effect of potassium salts on alleviation of lime‐induced chlorosis in soybean 1

Studies were conducted to determine the efficacy of K salts in alleviating lime‐induced chlorosis. Greenhouse studies using a Gibbon silt loam [fine‐silty, mixed (calcareous), mesic Typic Haplaquoll] and a 1: 1 mixture of Gibbon soil and washed sand were conducted with KCl, KNO₃, K₂SO₄, K₂HPO₄, or KHCO₃ applied at rates of 0, 250, and 500 mg K/kg soil. An FeEDDHA treatment was included for comparison. Similar studies were conducted at two field sites known to produce lime‐induced chlorosis. Potassium salts were applied at 0, 20, and 40 g K/m of row. In the greenhouse, plants treated with KCl, KNO₃, and K₂SO₄ on Gibbon soil were less chlorotic than controls or plants treated with K₂HPO₄, or KHCO₃. No K treatment totally alleviated chlorosis except FeEDDHA. Chlorophyll correlated positively with chlorosis rating. No relationship was found between leaf Fe uptake and chlorosis. Plants grown in soil/sand exhibited no chlorosis and had lower Fe uptake than plants grown in Gibbon soil. Thus chlorosis was not due strictly to low soil‐Fe availability or inadequate Fe uptake. Bicarbonate in the soil solutions of both growth media treated with KCl was lower than controls which may explain the reduced chlorosis associated with this treatment.

One field site showed positive effects of K treatments on chlorosis rating, chlorophyll concentration, and seed yield. No treatment was as effective as FeEDDHA in influencing plant growth or yield. Total leaf Fe concentration was unrelated to leaf chlorophyll concentration. Inorganic cation/anion ratios in the plant were from 4.4–8.4 which could cause net H⁺ efflux by the plant and alkalinization of plant tissues. One possibility is that H⁺ efflux solubilizes P in the rhizosphere, which after uptake could immobilize Fe in the plant. Application of KCl, KNO₃, and K₂SO₄ generally lowered HCO₃ content of the upper 15 cm of both soils. High bicarbonate could increase rhizosphere P availability and increase immobilization of Fe in the plant.