Differential leaching of cations and sulfate in gypsum amended soils

Abstract

An adequate supply of available Ca in the soil solution of the pegging zone during fruit development is required for production of high yields of high quality peanuts (Arachis hypogaea L.). On low Ca soils, application of gypsum during early bloom is recommended in order to ascertain adequate availability of Ca. Reaction of gypsum in soils under leaching conditions vary considerably and play an important role in fruit development and yield of peanuts. A laboratory study was conducted in leaching soil columns to investigate the effects of one gypsum amendment on leaching of Ca, K, Mg, and SO₄ to a depth of 8 cm (fruiting zone of peanut). Six soils of varying physical and chemical properties representative of major peanut growing soils in Georgia were utilized. Following leaching with 15 cm water through gypsum‐amended soil columns, 50% to 56% and 74% to 77% of applied Ca and SO₄, respectively, were leached below 8 cm in the sandy‐Carnegie, Dothan, Fuquay and Tifton soils. The respective values for the sandy clay loam‐Greenville and Faceville soils were 28% to 36% and 58% to 69%. Lower initial Ca status and greater leaching of Ca from the applied gypsum in the sandy soils as compared to sandy clay loam soils suggest greater beneficial effects of supplemental gypsum application for peanut production in the former soils than in the latter soils. Leaching of K or Mg (as percentage of Mehlich 1 extractable K or Mg) in gypsum‐amended treatment was considerably greater in sandy soils than that in the sandy clay loam soils. In view of the reported adverse effects of high concentrations of soil K and Mg in the fruiting zone on the yield and quality of peanuts, greater leaching of K and Mg from the fruiting zone in gypsum amended sandy soils enable them to maintain a favorable cation balance for the production of high yields of quality peanuts.     

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.     

Combined Effects on Nitrogen Fertilization and Soil of CaCO3 Contents on Corn Performance in Al-Marj Soil,Libya

A two-year field trial was conducted at Al-Marj Research Center, northeast Libya, during the summers of 1996 and 1997 to examine the effect of nitrogen (N) fertilizers on corn (Zea mays L.) growth in a Libyan soil (fine mixed thermic, Typic Haploxerolls) amended with different calcium carbonate (CaCO₃) levels. Two N fertilizer sources (urea and diammonium phosphate, or DAP) were used at three application rates (0, 80, and 160 kg N/ha). The CaCO₃ treatments were 1%, 6%, and 12% based on the soil weight of a 15 cm furrow slice. A basal phosphorus (P) dose of 46 kg P₂O₅/ha as triple superphosphate was applied to all experimental plots before planting. The experimental plots were arranged in a randomized split-split plot design with three replications. The parameters measured included corn grain weight, plant dry-matter content, leaf contents of N, P, potassium (K), calcium (Ca), and magnesium (Mg). The plant dry matter and corn-grain yield were significantly decreased by CaCO₃, but were significantly increased by N fertilizer rates. Average grain yield dropped from 8 to 3 Mg/ha at 1% and 12% soil CaCO₃ content, respectively. Generally, the N source did not have a significant effect on dry matter or on grain yield. The negative effect of CaCO₃ on yield was associated with concomitant significant reduction in leaf N, P, K, and Mg contents, and an increase in Ca content. However, the leaf levels of these nutrients were considered sufficient for corn growth. Therefore, the reduction of leaf-N by CaCO₃ in fertilized soils might have been the major cause of corn dry-matter and grain-yield reductions.     

Effect of gypsum on soil potassium and magnesium status and growth of alfalfa

Abstract

Though surface‐applied gypsum has been shown to be useful in reducing the subsoil acidity syndrome, excessive application could reduce the availability of other essential cations in soil. This study was conducted to determine the effects of surface‐applied gypsum on the availability of potassium (K) and magnesium (Mg) in field soils. Field experiments were conducted on Davidson and Tifton series soils in the southeastern United States with 6 main ameliorant treatments (0, 2, 5, and 10 t gypsum/ha, soil profile mixed to 1 m without lime incorporation and, mixed with lime to 1‐m depth), and 2 levels of Mg (0 and 100 kg Mg/ha) and 4 levels of K (0, 125, 250, and 375 kg K/ha) in a split‐split plot configuration. Alfalfa was grown on the Tifton soil and sorghum on the Davidson soil. Yields of alfalfa and sorghum increased with 2 t gypsum/ha but were adversely affected above 5 t gypsum/ha. Gypsum amendment at 2 t/ha reduced topsoil exchangeable Mg and K in both soils. In the soil profile study, exchangeable Mg was reduced throughout the upper 52.5‐cm depth, while no reduction of K was observed below the 22.5‐cm depth in either soil. The study indicates that Mg is more susceptible to leaching loss than K after surface application of gypsum. It is also suggested that surface‐applied gypsum be used as a soil ameliorant along with proper management of Mg and K fertilizers.     

Relationship between soil‐test P and K and yield response of runner peanuts to fertilizer

Abstract

Direct fertilization of peanuts (Arachis hypogaeaL.) with P and K has generally shown few yield responses, resulting in only limited information concerning critical soil‐test levels of P and K. The purpose of the experiments in this report was to determine the critical soil‐test levels of P and K for runner peanuts using the double‐acid extraction procedure. Fertilizer experiments were conducted on farmers’ fields from 1973 to 1986. Site selection was based on soil test data that indicated “medium”; or “low”; levels of available P or K but “high”; in Ca and Mg. Phosphorus and potassium were applied together at all sites at rates of 20 and 74 kg/ha, respectively, as concentrated superphosphate and potassium chloride.

There were yield increases to fertilizer in 6 of the 39 experiments. Soil‐test P for these six ranged between 4 and 53 kg/ha; soil‐test K ranged between 10 and 31 kg/ha. Delineating the yield effect into their P and K components with the aid of multiple regressions of yield on soil test values showed that yield increases were due to the K component of the fertilizer. The critical soil‐test K value was calculated to be 37 kg/ha. Sound mature kernels (SMK) were generally unaffected by fertilizer.     

Preliminary studies on triticale,wheat, barley,and rye responses to lime and N.

Abstract

The lime and N requirements for triticale (X Triticosecale Wittmack) have not been established because of the relatively short history of the crop. This study was designed to evaluate the effects of lime and high N rates on triticale, wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and rye (Secale cereale L.) on Dickson silt loam (Typic Paleudult) and Decatur silty clay loam (Rhodic Paleudult) in 1974–1976. The soils had pH values of 4.9 and 5.5 with no lime and 5.4 and 5.8, respectively, when limed as recommended. The fertilizer rates were 112, 140, and 170 kg N/ha. Yields and N, P, K, Ca, Mg, Mn, Fe, Al, Zn, Cu, and B were determined in straw and grain. Liming the Dickson soil increased the straw yields of barley at 112 kg N/ha and grain yields of the cultivars generally at the 170 kg N/ha rate. Liming the Decatur soil did not have consistent effects on straw yields but increased the grain yields of the wheat and rye cultivars. Increasing N rate increased the straw yields of wheat on Dickson but decreased the grain yields of barley in the same soil with no lime. Nitrogen fertilization did not have consistent effects on the Decatur soil. The N, P, K, Ca, Mg, and Mn compositions suggested that more differences occured at the species level than at the cultivar level.     

Effect of fertilization and irrigation upon NPK composition of corn leaves,on corn yields,and available k in soil

Abstract

Corn (Zea mays L.) was grown for three consecutive years on Congaree loam to measure the effects of rates of N, P, and K fertilization and irrigation on the nutrient concentration of leaves, the level of available K in the soil, and on the yield of corn. Plant nutrients consisting of 0, 56, 140, 224, and 280 kg N/ha; 0, 15, 37.5, 60, and 75 kg P/ha, and 0, 28, 70, 112, and 140 kg K/ha were applied in a central composite rotatable design in each of the three years. All plant residue was removed each year when the corn was harvested, and the plots remained fallow during the winter months. One half of the experiment was irrigated when there was a 50% depletion of available soil moisture in the 0‐ to 46‐cm soil depth.

Leaf composition was affected by fertilization and irrigation. A rapid decrease in available soil K in the 0‐ to 15‐cm depth was evident the first year with all rates of added K. The decline in available soil K was unaffected by irrigation and levels of applied N and P.

There were consistent yield responses each year to added N, no response to added P, and a response to added K only during the second year.     

Irrigation frequency effects on leaching of cations from gypsum amended coastal plain surface soils

In low Ca soils, gypsum is applied at flowering of peanut (Arachis hypogaea L.) to insure adequate availability of Ca in the fruiting zone (0 to 8 cm soil depth) during pod development. Effects of 15.2 cm water applied as 1, 2, 4 or 12 split applications over 28-d period following the application of gypsum on the distribution of Ca and other cations in the fruiting zone and immediately below the fruiting zone (8 to 16 cm depth) were investigated on the Lakeland and Tifton soils under controlled conditions in rainout shelter plots. In Lakeland soil, the fruiting zone Ca concentration was greater for the high frequency (15.2 cm in 4 or 12 split applications) irrigation treatments than for the low frequency (15.2 cm in 1 or 2 split applications) treatments at 7 d. Those differences became non-significant after 14 d. In Tifton soil, leaching of Ca below the fruiting zone was significantly greater for the low frequency irrigation treatments than for the high frequency treatments throughout the duration of this e experiment. High frequency irrigation of moderate quantities should result in low Ca losses from the fruiting zone. Irrigation following gypsum application decreased K and Mg concentrations in the fruiting zone for both soils. The gypsum-induced leaching of K or Mg was lower in high frequency irrigation treatments than in low frequency treatments. High frequency irrigation following gypsum application resulted in a decrease in soil pH during the initial 7 d.     

Effect of Mg And Zn fertilization on soil test levels,ear leaf composition,and yields of corn in northern West Virginia

Abstract

A corn fertility study was conducted at two locations in northern West Virginia to determine the response of corn (Zea mays L.) to applied Mg and Zn on two soils testing low in Mg by the ammonium acetate and Baker tests and low in Zn by the Baker test. The study consisted of three rates of Mg (0, 112, and 224 kg/ha) and three rates of Zn (0, 3.36, and 6.72 kg/ha) applied in a factorial design. The soil at the Morgantown location was medium textured with a CEC of 22.4, and the soil at the Reedsville location was coarse textured with a CEC of 15.8. Yield responses to applied Mg were obtained only on the coarse textured soil at the Reedsville location where exchangeable Mg was less than 5% of the CEC and equilibrium Mg was less than 9.0 10 ^‐4M. No yield response to Zn was obtained at either location.     

Gypsum material effects on peanut and soil calcium

Abstract

Adequate availability of calcium (Ca) in the upper 7–10 cm of soil is extremely important for pod development and therefore for production of quality peanut (Arachis hypogaea L.). Supplemental Ca is usually applied as gypsum, however, availability of Ca may depend on the type of gypsum. The objective of a laboratory study was to evaluate recovery of Ca in Mehlich I, 0.01 M NaNO₃ and deionized water extractants from seven gypsum materials which varied physically from fine and coarse powders to crystals, granules and pellets. Overall, recovery of Ca was much greater in Mehlich I (89.5–99.6% of total Ca) than in either 0.01 M NaNO₃ (81.0–98.4%) or deionized water (78.7–97.5%). However, for 3 sources, recovery of Ca was very similar in NaNO₃ solution and deionized water.

Field experiments were conducted on Lakeland sand (Mehlich I Ca = 127 kg/ha, 0–15 cm) and Tifton loamy sand (Mehlich I Ca = 665 kg/ha) soils to study the effects of the gypsum materials on Florunner peanut grade and yield. Effects of gypsum treatments on Mehlich I‐ and 0.01 M NaNO₃‐extractable soil Ca were also evaluated during peanut pod development. On the Lakeland soil, Mehlich I Ca increased from 127 to a range of 420–737 kg/ha following application of gypsum depending on the type of gypsum material. Percent sound mature kernels were significantly greater where gypsum was applied than in the control treatment, regardless of source. Total sound mature kernel yield and gross return were greatest for the more soluble sources. The yield vs. soil test Ca relationship 90 d after planting revealed that yield response was very minimal if soil Ca was greater than 290 and 85 kg/ha of Mehlich I and 0,01 M NaNO₃‐extractable Ca, respectively. Application of gypsum to the Tifton soil, regardless of type of material, had no significant effect on yield, grade or gross return because Mehlich I extractable Ca in the control treatment was well over 560 kg/ha; the critical soil test Ca for runner peanut according to the current Georgia soil test recommendation.     

Stand recovery of coastal bermudagrass following stand loss induced by potassium deficiency

Abstract

‘Coastal’ bermudagrass (Cynodon dactylon L. Pers.) stand loss resulting from K deficiency has been reported. The recovery of this perennial grass from K deficiency could very well take a significant time after the deficiency is corrected. Experiments were conducted on two soils, Darco (Grossarenic Paleudult; loamy, siliceous, thermic) and Cuthbert (Typic Hapludult; clayey, mixed, thermic). Previous P and K factorial rate studies had been conducted on the experimental sites. Annual K and P fertility rates used on prior studies were 0, 112, and 224 kg/ha K and 0 to 136 kg/ha P. These earlier treatments were overlaid with rates of 112 and 224 kg/ha of P and K, respectively. Data were taken for yield, stem length, stem weight, and rhizome production. Yield was found to be related directly to stand. Yield was also related to plant height under severe stand loss. Yield loss was not related to stem weight. Rhizome production recovered after two years. Yield had recovered by the end of the first year.     

The effect of nitrogen and boron soil applications on raspberry leaf N,B and Mn concentrations and on selected soil analyses

Abstract

Four years after yearly applications of N (0, 67, 134 and 268 kg/ha in a N rate trial) soil pH and soil extractable K, Ca and Mg were reduced. Boron application (1 kg/ha in a N x B interaction trial) increased hot water extractable soil B and soil extractable Mg. Old and new cane leaf N concentration was increased by N application but B application resulted in only a very small effect. Both N and B applications increased leaf B concentrations. Leaf Mn was increased by N application, probably because of the reduced soil pH. Boron had little effect on leaf Mn. It was concluded that leaf tissue is not suitable for determining the requirements of N and B fertilizer because of the instability of B concentrations in the leaves within and between seasons. Sampling of new cane leaves in July showed promise for diagnosing Mn requirements since the concentration during that month was relatively stable in three separate years of sampling.     

Response of rice to basic slag,lime, and leaching in two saline-acid sulfate soils in pot experiments

Pot experiments were conducted to evaluate the effects of basic slag (6 to 18 t/ha), lime (CaCO₃: 3 to 9 t/ha), lime (3 t/ha) plus MnO₂ (100 mg/kg), and leaching (1.8 L/kg soils) on the growth, yield, and nutrition of rice plants grown on two saline-acid sulfate soils. The Sulfic Fluvaquent (Chakaria series) and Typic Sulfaquent (Badarkhali series) respectively showed low pH (4, 4.3); high electrical conductivity (16.2, 14.2 mS/cm), sodium adsorption ratio (13.6, 12.8), and water soluble SO₄2^? (4.6, 4.9 cmol/kg). The growth and yield response of rice to the treatments were found better in Chakaria than in Badarkhali soil. The leaching treatment was found to be the best to produce the maximum straw, and grain yield (869% increase over the control) and the highest dose of basic slag (18 t/ha) was ranked second (728%) in Badarkhali soil. But in Chakaria soil, the best response (928%) was determined with the highest dose of lime (6 t/ha) followed by the leaching (900%) treatment. The additional application of Mn0₂ (100 mg/kg) with lime (3 t/ha) significantly increased the straw and grain yields of rice by 42–47% compared with the lime 3 t/ha in both the soils. Similar effects were observed for N, P, and K concentrations in plant straw at maturity. Leaching, basic slag, and lime treatments exerted significant decrease of the Fe, Mn, Zn, and S concentrations in plants, increase of soil solution pH and optimization of some element concentrations in the plants and soil solutions.     

Response of tall fescue to fertilizer placement at different levels of phosphorus,potassium, and soil pH 1

Fertilizer application, particularly nitrogen (N), is important in cool‐season grass forage production. Subsurface (knife) placement of N often has resulted in higher forage yield and N uptake of tall fescue (Festuca arundinacea Schreb.) compared to surface‐broadcast fertilization, but further studies were needed to indicate whether soil pH, phosphorus (P), or potassium (K) modifies the response. Experiment I tested responses of forage yield and N and P concentration to N, P, and K amount and placement. Two types of fertilizer placement ‐ broadcast and knife ‐ were used with 13, 112, or 168 kg N; 0 or 19 kg P; and 0 or 37 kg K/ha in a factorial arrangement. Yields increased by 53% as N fertilization went from 13 to 112 kg/ha and by 69% as N increased from 13 to 168 kg N/ha. Forage yield was increased 26% from knife compared to broadcast fertilizer placement. P application increased forage production by 13%, but K application had no effect on yield. Forage N concentrations increased by 25% as N fertilization went from 13 to 112 kg/ha and by 38% as N increased from 13 to 168 kg N/ha. Effects of added P and fertilizer placement on N concentration often resulted in interactions among factors. Forage P generally was increased by added P, with some effects of interactions among N rate, P rate, and placement. In Experiment II, fescue responses to N placement were tested where different soil characteristics had been established by previous lime and fertility treatments. Forage yield, N concentration, and N uptake were highest where 9.36 Mg/ha of lime were applied as compared to the control. Previous fertility treatments had no significant (P<0.05) effect. When N was knifed, forage yield was related positively to available soil P but not to pH or K. Yield and forage N concentration and uptake were increased by 20, 11, and 33%, respectively, as a result of knife versus broadcast N application.     

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.     

Effets des engrais N,P et K sur le rendement et la qualite de l'ensilage ue mais

Abstract

Thirteen fertility trials were made throughout Quebec's corn growing region during 1972–74. These included eleven fertilizer combinations with corn silage as the test crop and were carried out on nine soils. Total dry matter and digestible nutrients (TDN) varied greatly from year to year, though, mean yields increased by 23 and 30 percent respectively with the 50 kg N/ha treatment, compared to control receiving no nitrogen fertilization. However, 150 kg N/ha was required to attain a maximum yield of 1250 kg/ha crude protein. Despite a 0.2 percent nitrate content found in the silage grown on the most northerly site, a 120 kg P/ha combined with 100 kg N and K gave the highest mean TDN production (9580 kg/ha).

Potassium fertilization affected plant K content of corn grown at the most northerly site only, where a 0.5 percent was found with the control on a suit containing low potassium levels. Further, striking increases in Ca and Mg concentrations were observed with corn grown on that soil. However, magnesium concentration ranging from 0.11 to 0.14 percent were found with nine field trials out of twelve. Also, low K:(Ca + Mg) ratios were found on three trials, which were increased with potassium fertilization levels of 150 kg K/ha. Accordingly, it is suggested that uptakes of 200, 48, 200, 30 and 30 kg/ha of N, P, K, Ca and Mg are required for good corn silage crops.     

Soil solution and extractable calcium in gypsumamended coastal plain soils used for peanut culture

Abstract

Peanut (Arachis hypogaea L.) fruits absorb Ca directly from the soil solution; therefore, the concentration of soil solution Ca in the fruiting zone (0–8 cm) is important in determining the availability of adequate Ca during fruit development. Since the critical period for Ca requirement for peanut fruit may extend from 25–65 d after flowering, a measure of extractable Ca (Quantity factor) is also important in determining the replenishment of soil solution Ca over the fruiting period. A laboratory study was conducted to evaluate the effects of varying soil moisture regimes on soil solution and extractable Ca in gypsumamended Bonifay sand (loamy, siliceous, thermic, grossarenic, Plinthic Paleudult) and Greenville sandy loam (clayey, kaolinitic, thermic, Rhodic Kandiudult) soils over a 70‐d period. Soil solution Ca increased in both soils with increasing soil moisture, 14 d after incubation of gypsum‐amended soils. Subsequently, the soil solution Ca decreased for all moisture regimes in the Bonifay soil, but only in the driest regime in the Greenville soil. Soil solution Ca concentrations were 1.0 and 3.2 cmolc/L in the Bonifay soil and 2.7 and 1.6 cmolc/L in the Greenville soil for the wettest and driest regimes, respectively, 70 d after incubation. Gypsum amendment also increased the concentrations of K and Mg in soil solution in both soils; therefore, leaching of excess K and Mg below the fruiting zone may be facilitated in field situations.     

Tolerance of spring wheat to a salt‐fluxing residue containing potassium and magnesium

Abstract

Field and greenhouse studies were conducted in Idaho in 1985 to document the maximum levels of a salt fluxing residue (slag) material that can be safely applied to agricultural soils without reducing spring wheat (Triticum aestivum) growth. The slag material, which contains significant quantities of Mg and K, was applied to Mission (coarse‐silty, mixed, frigid Andic Fragiochrepts) and Palouse (fine‐silty, mixed, mesic Pachic Ultic Haploxerolls) silt loam soils at rates ranging from 0 to 40,000 kg/ha. Parameters evaluated included: (1) germination, (2) plant vigor, (3) yield, and (4) soil and plant tissue K, Ca and Mg.

Under field conditions slag application rates of 4,000 and 8,000 kg/ha reduced wheat stands and vigor; however, yields were not adversely affected when compared with the control. Application rates in excess of 8,000 kg/ha resulted in reduced germination, plant vigor, and yield and are consequently not recommended. Greenhouse studies provided further evidence to substantiate the field results.     

Effects of nitrogen carriers,nitrogen rates,and maturity on composition of smooth bromegrass

Abstract

Magnesium and Ca concentrations in smooth bromegrass (Bromus inermis L) were not affected by late‐winter applications of N. Magnesium concentrations were constant until rapid growth in mid‐May then they declined until early June harvest. Highest seasonal concentrations were found in the fall regrowth. Calcium concentrations declined as plants matured in spring. Highest seasonal Ca concentrations were found in the fall regrowth. Nitrogen, P, and K concentrations and K/(Ca+Mg) ratios were increased by N applications during early spring but did not differ significantly by early June harvest. Nitrogen and P concentrations decreased as plants matured in spring and fall. K concentrations and K/(Ca+Mg) ratios changed inconsistently from sampling date to sampling date. Forage yields were approximately doubled by 67 kg N/ha and tripled by 202 kg N/ha. Significant yield differences were related to different N carriers.     

Yield,forage quality,and nitrogen recovery rates of double‐cropped millet and ryegrass

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.