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.     

Grassland plants affect dissolved organic carbon and nitrogen dynamics in soil

Dissolved organic carbon (DOC) and nitrogen (DON) are central in many nutrient cycles within soil and they play an important role in many pedogenic processes. Plants provide a primary input of DOC and DON into soil via root turnover and exudation. Under controlled conditions we investigated the influence of 11 grass species alongside an unplanted control on the amount and nature of DOC and DON in soil. Our results showed that while the presence of plants significantly increases the size of a number of dissolved nutrient pools in comparison to the unplanted soil (e.g. DOC, total phenolics in solution) it has little affect on other pools (e.g. free amino acids). Grass species, however, had little effect on the composition of the DOC, DON or inorganic N pools. While the concentration of free amino acids was the same in the planted and unplanted soil, the flux through this pool was significantly faster in the presence of plants. The presence of plants also affected the biodegradability of the DOC pool. We conclude that while the presence of plants significantly affects the quantity and cycling of DOC and DON in soil, comparatively, individual grass species exerts less influence.     

Fruit set and quality of loquats (Eriobotrya japonica) as effected by pollinations under sub-humid Mediterranean

A field experiment was conducted during 2005 and 2006 growing seasons at Ras Munif (32°22′N, 35°45′E), Ajloun, Jordan, to evaluate different pollination treatments and their effects on fruit set and quality of loquat fruit grown under Mediterranean conditions. Open, supplemental, rain, and covered pollination treatments were imposed on the selected trees. Results showed that under supplemental and open-pollination, extremely higher fruit set was obtained compared with rain and covered treatments. In spite of a heavy crop load, fruits obtained under open and supplemental pollination were also heavier and larger, this could be partly due to a significant increase in seeds and flesh weight. Sugar content was good for both open and supplemental pollination. Wind plays little or no role in loquat pollination process. Loquat flowers attracted very limited number of bee visitors, A. mellifera, Anthophora albigena and Xylocopa violocea of family Apidae and Halictus quadricinctus of family Halictidae were recorded the only loquat flower visitors. They showed a variation in their visiting time but loquat flowers attracted the highest rate and number during the mid of the day.     

Differential Utilization of Dissolved Organic and Inorganic Nitrogen by Wheat (Triticum Aestivum L.)

A study was conducted under greenhouse conditions on wheat to investigate the utilization of dissolved organic nitrogen (N) in comparison with conventionally applied inorganic N sources (INS). Nitrogen was applied at a rate of 90 kg N ha^?1 in an inorganic form, an organic high molecular weight (MW) form (casein, haemoglobin, albumin), and an organic low MW amino acid form (glycine, alanine, valine). Inorganic N sources recorded the maximum response (126% to 150%) in total dry matter (DM) production while dissolved organic nitrogen (DON) sources showed 61% to 116% increase in comparison to the control treatment. Glycine gave the maximum DM production, which was comparable with both INS treatments. In hydroponics, greater utilization occurred and the shoots had a higher N content in comparison to those grown in soil. The concentration of DON and NO₃^? in soil after wheat harvest was similar in all the treatments.