B. W. Mathews

Soil macronutrient distribution in rotationally stocked kikuyugrass paddocks with short and long grazing periods

Abstract Grazing management affects plant growth and animal production and it may influence the redistribution and cycling of nutrients excreted in dung and urine. Unfortunately, the soil component of pasture systems has received little attention in most grazing trials, and when considered has been evaluated on pastures smaller than those used commercially. A naturalized kikuyu (Pennisetum clandestinum Hochst. ex Chiov.) grassland was grazed by heifers (Bos taurus) for 2 yr in Experiment 1 to determine the effects of two rotational stocking methods (short vs. long grazing periods) on soil distribution of extractable nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) in 4‐ha paddocks with natural shade. Additionally, in Experiment 2, kikuyugrass‐greenleaf desmodium (Desmodium intortum Urb.) paddocks were used to evaluate the effect of distance from waterers on soil nutrient distribution in rotationally stocked paddocks (long grazing periods) without shade in a cooler,...

MACRONUTRIENT, SOIL ORGANIC CARBON, AND EARTHWORM DISTRIBUTION IN SUBTROPICAL PASTURES ON AN ANDISOL WITH AND WITHOUT LONG-TERM FERTILIZATION

Pasture fertilization affects plant growth and animal production, and it may influence the redistribution and cycling of nutrients excreted in dung and urine. Kikuyugrass (Pennisetum clandestinum Hochst. ex Chiov.) pastures on a high organic carbon (C) Typic Hydrudand soil with and without (control) annual nitrogen (N) and periodic phosphorus (P) and potassium (K) fertilizations were stocked with Hereford and crossbred cattle (Bos taurus) for 33 years. The pastures were divided into 1.2-ha paddocks for rotational stocking after the 15th year. Selected fertilized paddocks that were uniformly managed over the years were paired with control paddocks to determine management effects on soil organic C; soil and plant N, P, and K; and earthworm distribution. Responses were assessed using a zonal sampling procedure based on distance from the waterer because the paddocks lacked shade. Soil organic C, organic N, and organic P did not statistically differ between managements or zones in any horizon. Relative to the control, however, an apparent recovery of 25% of the total N applied to the fertilized paddocks was obtained as soil organic N within the 80 cm profile depth examined. Inorganic N (NH4-N + NO3-N) was greater in the Ap1 and Bw1 horizons of fertilized paddocks, and there was a trend in the Ap1 horizon toward greater concentrations within 15 m of the waterer. Additionally, substantial inorganic P accumulated within 30 m of the waterers in the Ap1 and Bw1 horizons of fertilized paddocks while minimal P accumulation occurred within 15 m of the waterer in control paddocks. The magnitude of K accumulation near waterers was also considerably greater in the Ap1 horizon of fertilized paddocks. It is suggested that fertilization increases the magnitude of P and K accumulation near waterers due to the combination of increased forage P and K concentrations and pasture carrying capacity. Management and zone effects for forage N, P, and K tended to follow patterns relatively similar to the soil Ap1 horizon data for the inorganic forms of these nutrients. Earthworm populations did not differ among zones, but populations in fertilized paddocks were double those of control paddocks.

Proximate Analysis, in Vitro Organic Matter Digestibility, and Energy Content of Common Guava (Psidium guajava L.) and Yellow, Strawberry Guava (Psidium cattleianum Var. lucidum) Tree Parts and Fruits as Potential Forage

The nutrient composition of common guava, Psidium guajava L., and strawberry guava (waiwi), Psidium cattleianum var. lucidum, tree parts and fruits was determined during three seasons for six locations in Hawaii to assess guava as a potential feed for cattle. All guava plant parts were higher (p < 0.001) in crude protein than waiwi, but there were no differences in the fiber and energy densities for bark, shoots, and branches. Guava leaves were higher in fiber and had lower energy densities (p < 0.05) than waiwi. Ripe and breaker stage fruits were lower (p < 0.05) in fiber, similar in protein (CP), and higher (p < 0.05) in energy density than immature fruits. Guava fruits were higher in CP (p < 0.05) and organic matter (p < 0.001) and lower in ash (p < 0.001) than waiwi fruits. The primary nutritional concern with guava is low in vitro organic matter digestibility as compared to tropical forage grasses; therefore, it is not recommended as a feedstock for livestock.

In vitro digestibility and nutrient concentration of bermudagrass under rotational stocking, continuous stocking, and clipping

Abstract Grazing method effects on bermudagrass [Cynodon dactylon (L.) Pers.] nutritive value have received little attention. To examine the effects of three grazing methods and a hay system on herbage digestibility, nitrogen (N), and mineral concentration, a 2‐yr study was conducted using ‘Callie’ bermudagrass pastures growing on a Florida flatwoods soil with a seasonally high water table. Grazed pastures were stocked with Holstein heifers (Bos taurus) and grazing methods were i) rotational stocking with short grazing periods (1.5 to 2.5 d per paddock), ii) rotational stocking with long grazing periods (10 to 14 d per paddock), and iii) continuous stocking. Herbage samples (above a 15 cm height) were collected from all pastures and hay areas on four sampling dates per year (26 to 28 d of regrowth). Despite differences in leaf percentage as great as 18 units, in vitro digestible organic matter concentration averaged 565 g/kg OM and did not differ among managements by more than 32 g/kg OM in either year. G...

Phosphorus response of sericea lespedeza on a georgia ultisol

Abstract A field study was initiated on a Davidson sandy clay loam, clayey, kaolinitic, thermic Rhodic Paleudult soil in central Georgia in 1982 to evaluate P response of high‐ and low‐tannin sericea lespedeza (Lespedeza cuneata(Dumont) G. Don) cultivars. Following application of 0, 35, 70 or 105 kg ha‐1P, soil test values at the 0–15 cm depth ranged from 10.0 mg kg‐1in the control plots to 42 mg kg‐1at the 105 kg ha‐1P application rate. Yields of five sericea lespedeza cultivars were not significantly (P>0.05) affected by soil P level during the four years (1983–1986) and averaged from 3500 kg ha‐1in 1986 to 7200 kg ha‐1in 1984. Soil samples collected from 0–60 cm in 15‐cm increments indicated that applied P did not move below the surface 15 cm but that adequate soil solution P for plant growth was present below this level. Profile excavation indicated that roots of all cultivars proliferated to the 60‐cm depth regardless of the P application rate. In a comparison of Mehlich I and Bray 2 extractants for ...

Mineral Composition and Soil-Plant Relationships for Common Guava (Psidium guajava L.) and Yellow Strawberry Guava (Psidium cattleianum var. lucidum) Tree Parts and Fruits

The mineral compositions of the fruit and tree parts of common guava, Psidium guajava L., and strawberry guava, Psidium cattleianum var. lucidum, were determined. The study occurred during three seasons at six locations in Hawaii to assess guava as feed for livestock. Guava bark contained the greatest concentrations of calcium (Ca) and ash; leaves the greatest concentrations of magnesium (Mg), sulfur (S), sodium (Na), boron (B), and manganese (Mn); and the shoots had the greatest concentrations of nitrogen (N), phosphorus (P), and potassium (K). The leaves and the shoots had the greatest concentrations of copper (Cu) and iron (Fe). Between guava and waiwi, guava had greater concentrations of most minerals except for Na in all plant parts, and Mg and ash in the leaves. Guava leaves and shoots meet the macromineral requirements for various phases of sheep, goat, and beef cattle life cycles with the exception of P and Na. Guava shoots do not meet Mn requirements for lactating cows.

Edible plant tissue and soil calcium:magnesium ratios: data too sparse to assess implications for human health

Abstract. Unlike yield, the plant calcium (Ca) : magnesium (Mg) ratio increases at higher soil Ca : Mg and decreases at lower soil Ca : Mg. Edible plant tissue Ca : Mg at various soil ratios has not been robustly studied. Such studies are appropriate because high Ca : Mg dietary ratios may be associated with increased risk of chronic diseases such as cardiovascular disease and diabetes, and human dietary Ca : Mg ratio is rising as populations integrate more processed foods into traditional diets. This review explores whether increasing the soil Ca : Mg ratio is likely to increase edible plant tissue Ca : Mg ratio, a result that could, if substantial, affect human health. A literature search gathered published articles reporting Ca and Mg values for plants grown in soils or nutrient solutions with various Ca : Mg ratios. For each study, soil or solution ratio was plotted against plant ratio, and Pearson’s r and 2-tailed P values were calculated. Findings reveal that reporting Ca and Mg content of edible plant tissues is rare in studies assessing the impact of soil Ca : Mg on crop yields, nutrient uptake or crop quality; Ca : Mg of whole plants and most shoots increases as soil Ca : Mg rises; leaf Ca : Mg of some but not all crops increases as soil Ca : Mg rises; Ca : Mg ratios of edible grain, fruit and root tissues are smaller than those of leaves or shoots of the same crop; and Ca : Mg of grain, bean and fruit tissue may not respond to changes in soil Ca : Mg as much as Ca : Mg of plants, shoots and leaves. However, the data are too sparse for conclusions or even speculation. Further measurements of Ca and Mg in edible tissues destined for human consumption are necessary to asses any impact of soil Ca : Mg on the rising dietary Ca : Mg of humans and its health consequences.

In Vitro Digestibility and Chemical Composition of Kikuyugrass as Influenced by Soil Silicon, Liming, and Genotype

Kikuyugrass (Pennisetum clandestinum Hochst. ex Chiov.) is an active silicon (Si) accumulator, and Si can reduce the organic‐matter digestibility of forage grasses. Calcium carbonate (crushed coral) applications to a low Si Maile silt loam soil (Acrudoxic Hydrudands) had no effect on the in vitro digestible organic matter (IVDOM) concentration of 3‐week‐old (4.5‐leaf‐per‐tiller stage of development) ‘Whittet’ kikuyugrass regrowth, whereas calcium silicate (wollastonite) applied at the calcium equivalent of the calcium carbonate rates produced a curvilinear (crescent‐shaped quadratic) IVDOM response. Whittet IVDOM decreased when grass Si concentration exceeded about 22 g kg−1 or when 0.5 M acetic acid–extractable soil Si exceeded about 230 mg kg−1. Common and ‘Hosaka’ kikuyugrass regrowth on the Maile soil had less Si and greater IVDOM concentrations than those observed for high‐Si Kohala (Humic Dystrustepts) and Waialua (Pachic Haplustolls) silty clay soils. Whittet had greater crude protein and IVDOM concentrations and lesser fiber concentrations than common.

Use of Dilute Oxalate to Recover Exchangeable Aluminum Immobilized by Sulfate Salt Addition to Rhodic Kandiudult Subsoil

While SO4 salts have been shown to be effective in reducing exchangeable aluminum (Al) and solution Al activity in acidic subsoils, few attempts have been made in the laboratory to recover exchangeable Al immobilized by the suggested mechanisms of Al–OH–SO4 mineral precipitation or co-sorption on sesquioxide surfaces with SO4 and cations added in the salt (salt sorption). Some low-molecular-weight aliphatic acids such as oxalate are well-known for their ability to increase the solubility of Al in soils and oxalate has often been identified as the dominant or one of the dominant organic anions in subsoils. Oxalate is also well-known for its ability to form soluble complexes and a precipitate with calcium (Ca). Therefore, the objective of this study was to investigate the effects of dilute oxalate on the apparent recovery of exchangeable Al immobilized in response to the addition of gypsum (CaSO4·2H2O) and langbeinite (K2SO4·2MgSO4). Following a 6-month equilibration in the laboratory, gypsum and langbeinite added at 15 mmol SO4 kg−1 were equally effective in decreasing exchangeable Al in soil collected from the Bt1 horizon of a Paaloa silty clay (clayey, oxidic, isothermic Rhodic Kandiudult). However, an oxalate loading rate of 16 mmol kg−1 appeared to recover 100% of the exchangeable Al immobilized by langbeinite but only 38% of that immobilized by gypsum. This result was likely due to the formation of an oxalate precipitate or complexes with Ca in the gypsum treatment. It is suggested that the longevity of gypsum effects on reduced exchangeable Al under field conditions may be due in part to the role of Ca in oxalate complexation.