Scientific abstracts

Phosphorus and Potassium Fertilization Effects on Soybean Seed Quality and Composition

The effects of P and K fertilization on soybean [Glycine max (L.) Merr.] seed quality are unclear. Fertilization rates can have a positive effect on yield and composition in some growing locations and years but not in others. As the cost of soybean seed production increases, seed companies are interested in improving seed quality of soybeans possibly through increased soil fertilization. The objectives of this study were to determine the effect of different levels of P and K fertilization on soybean seed quality defined as seed viability, vigor, and seed composition. Seed samples were obtained from a long-term P and K fertilization trial. Phosphorus and K treatments were 0, 28, or 56 kg P ha⁻¹ yr⁻¹ and 0, 66, or 132 kg K ha⁻¹ yr⁻¹. Results indicated that excessive levels of P and K fertility decreased seed quality. Seed composition changed across sites and treatments, but changes were generally inconsistent. Total seed protein and oil were not significantly affected by P and K fertilization in most locations. However, linolenic acid concentrations increased with excessively high P and K fertilization while linoleic acid concentrations decreased only with P. These results indicate that excessively high levels of soil fertility may have negatively impacted seed quality.

Potassium Dynamics of a Forest Soil Developed on a Weathered Schist Regolith

Soils of the humid tropics are poor in available potassium due to intensive weathering and leaching of nutrients. A study was conducted to investigate the mineralogy and potassium supplying capacity of a forest soil developed on a weathered schist regolith. The quantity-intensity (Q/I) approach was used in this study. The schist regolith showed deep weathering and intense leaching throughout the profile, resulting in low cation exchange capacity (CEC) and available K in soil and saprolite layers. The mineralogy of the regolith was dominated by kaolinite, gibbsite and goethite. Feldspar, mica and mica-smectite minerals were observed in the lower saprolite layers. The Q/I parameters showed that the soils and saprolites were low in K supply power. This observation was attributed to weathering and intense leaching. The free energy values of K replacement (ΔG _r°) also suggest that soils and saprolites of the schist regolith were deficient in K. The Q/I parameters significantly correlated with organic carbon and clay content, CEC, pH and exchangeable K.

Long-term Effects of Nitrogen and Potassium Fertilization on Perennial Ryegrass Turf

Research on the effects of potassium (K) fertilization on turfgrass growth and its relationship to tissue K and soil K have been inconsistent due to the many factors affecting tissue K such as nitrogen (N) fertilization. This 5-yr study was initiated in 2004 to better understand N (as urea) and K (as K₂SO₄) effects on soil and plant response of perennial ryegrass (Lolium perenne L. ‘Brightstar’). A field study was conducted to evaluate five rate levels of N (49, 147, 245, 343, or 441 kg ha^-1 yr^-1) with three rate levels of K (49, 245, or 441 kg ha^-1 yr^-1). Clipping yield (CY), leaf tissue K, soil pH, rooting (in 2004 and 2005 only), and soil K were assessed in spring of each year. Leaf K and soil K increased linearly with K applied, whereas leaf K and CY regression slopes with soil K increased with greater N applied. Leaf K and CY increased linearly with N, whereas rooting, soil pH, and soil K decreased linearly with increased N. Rooting was inversely related to CY. Luxury consumption of K was observed in the latter years of the test (2006) at N rates of 245 kg N ha^-1 yr^-1 and lower. The strength of the regression (r²) and covariation between CY and leaf K increased with N rate and decreased with year of the test. There were no observed changes in shoot and root growth in response to K fertilization even at low soil test K levels (50 mg kg^-1).

Phosphorus and Potassium Fertilizer Effects on Alfalfa and Soil in a Non-Limited Soil

Fertilization strategies for high-yielding alfalfa (Medicago sativa L.) should take in account the increase in soil nutritional status that occurred during the last decades in areas with intensive agricultural use. A field study was conducted at the University of Padova, northeastern Italy, to determine the response of alfalfa yield and nutritive value to various combinations of P and K rates in a soil lacking nutrient deficiency. Alfalfa cultivar Delta was seeded in March 2005 on a silt loam soil having 38 mg kg⁻¹ available P and 178 mg kg⁻¹ exchangeable K. Nine treatments deriving from the combination of three P fertilization rates (0, 100, and 200 kg ha⁻¹ P₂O₅) and three K rates (0, 300, and 600 kg ha⁻¹ K₂O) were compared in a randomized complete block design. Plots were harvested at bud stage during three growing seasons (2005-2007) and dry matter (DM) yield, forage nutritive value, P and K contents, canopy height, and stem density were measured at each harvest. Soil samples were collected at the end of the research period for determination of available P and exchangeable K. The results demonstrated that P application had no impact on yield and did not interact with K in determining productivity, while K had a positive effect on yield. However, the 300 kg ha⁻¹ K₂O rate appeared sufficient to maximize yield, without adverse effects on the forage nutritive value. Data from soil analyses showed that alfalfa has a high K uptake even when it is fertilized at high rates.

Corn Nutrient Uptake as Affected by In-Furrow Starter Fertilizer for Three Soils

Placing fertilizer with the corn (Zea mays L.) seed is a common practice in northern climates to increase early season growth and nutrient uptake. While there are many options for commercially available fertilizers, there are no clear guidelines as to which products are best suited for different soil types. The objective of this study was to evaluate fertilizer source effects on plant mass and N, P, K, and S concentrations and uptake on clay loam (CL), fine sand (FS), and silt loam (SiL) soil in the greenhouse. Eleven commercially available liquid and dry fertilizer sources were applied in direct contact with the seed at six rates. The above-ground portions of plants were harvested 14 d after emergence to determine average plant mass and nutrient concentration and uptake. Fertilizer sources containing P increased or maintained plant mass and nutrient uptake in all soils compared with the control. Fertilizer sources containing N, K, and S generally reduced plant mass, with the exception of some sources containing K and S, which resulted in a greater uptake of K and S on FS when applied at low rates. The concentrations of N, P, K, and S in plant tissue increased even when plant mass and nutrient uptake decreased. Choosing a fertilizer source for seed placement can be important relative to the nutrient supply of the soil to maximize the potential positive benefits of increased plant mass and nutrient uptake at early growth stages.