SUMMARYWinter wheat cultivars Apollo, Hornet, Longbow and Norman were each sown at 50, 100, 200, 400, 800 and 1600 seeds/m2 in a field experiment conducted in Northern Ireland over the 1989/90 crop year. No growth regulators were applied and the wheat received 178 kgN/ha top-dressing in the spring. Hourly rainfall, windspeed and wind direction data were recorded and lodging was visually assessed from the end of May to harvest. Lodging first occurred in the 1600 seed-rate plots as the ears were emerging in early June and then progressively increased in the 800, 400 and 200 plots during June, July and August. Lodging did not occur suddenly but took several hours, with the stems first lying at an angle before lodging completely. Stem buckling or breakage did not appear to be the principal form of structural failure. The longest strawed cultivar, Longbow, lodged most severely. The shorter-strawed Norman also lodged badly in contrast with Hornet which had a similar straw length. Apollo, which was taller than Norman and Hornet and produced more ears per square metre than the other cultivars, lodged least but tended to lean at c. 30° from the vertical. Lodging occurred during or within 24 h of periods of rainfall which, in many cases, coincided with windspeeds at crop height averaging > 25 km/h and occasionally > 50 km/h. Lodging also occurred following rainfall when the windspeed did not exceed 16 km/h. The grain yield was negatively correlated with the average lodging from ear emergence to harvest, there being a 1 t/ha decline in yield for each 10% increase in average area lodged. The 50 and 100 seed-rate plots yielded 10 t/ha and had little or no lodging. The decline in yield with increased lodging and seed rate was attributed to the effect of lodging rather than to seed rate and was associated with a fall in the number of grains/ear and 1000-grain weight from 56 and 53·5 g at the lowest seed rate to 15 and 42·7 g at the highest, respectively. A comparison of the plants from lodged and unlodged plots of the 1600 and 800 seed rates, and subsequently of the 800 and 400 seed rates, indicated that at the higher seed rate, lodged plots had less fresh weight per unit area, basal internodes with smaller diameters, fewer support roots per stem, and a lower root dry weight per stem.

The effects of growing forage maize (Zea mays) with or without plastic mulching treatments on the dry‐matter (DM) yield, cob yield, DM content and starch content was investigated in Northern Ireland in 1996 and 1997. Cultivars differing in maturity characteristics were sown in spring at a range of dates in three replicated plot experiments and were used to compare the effects of two plastic mulches and an untreated control: one plastic mulch completely covered the rows (floating); the other had holes punched in the plastic, through which the plants grew (punch). Between April and October in 1996 and 1997, the Ontario heat units (OU) received were above average at 2489 and 2660 respectively; in those years without plastic mulches, the earliest maturing cultivar, Melody, yielded 11·0 and 13·6 t DM ha–1, with dry‐matter contents of 214 and 215 g kg–1 respectively. Mean daily increases in soil and air temperature under plastic mulches of up to 6°C and 11°C, respectively, were closely related to solar radiation. Under plastic mulches, 15% fewer OU were required to reach silking, and 33% more OU were available between silking and harvest. Meaned over three experiments, two years and three cultivars, plastic mulches, when compared with the unmulched control, increased maize yield from 12·0 to 14·7 t DM ha–1, cob yield from 3·7 to 6·8 t DM ha–1, dry‐matter content from 230 to 270 g kg–1 and starch content from 198 to 272 g kg–1. The effect of plastic mulch on the maturation of the crop was greatest at earlier sowings. In 1997, plants from an early sowing date (10 April) that had recently emerged through the punch plastic mulch were damaged by frost, whereas those in the floating plastic mulch plots were unaffected. When the floating plastic mulch was left on after the six‐ to eight‐leaf stage of the first‐early maize cultivar Hudson, the plants were physically damaged and the yield reduced, but DM and starch contents continued to increase. The increases in yield and dry‐matter content under the plastic mulch were greater in Diamant (second‐early cultivar) than in Melody (first‐early cultivar). It was concluded that, under marginal climatic conditions, plastic mulches ought to be used to improve the reliability of early cultivars rather than growing later maturing cultivars.

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Harrison (1995) found that the physical properties of a silt loam of pH 6.5 could be improved with high applica-Land application of sewage biosolids is a cheap disposal method tion rates of N-viro soil. In a glasshouse study, Pierzynski that permits recycling of plant nutrients, but there are concerns about its long-term agronomic value and environmental effects. This study and Schwab (1993) found that N-viro soil applied at the investigated the fertilizer value of alkaline-stabilized biosolids applied rate of 5 Mg DM ha Ϫ1 decreased Zn in the soil labile annually to spring barley (Hordeum vulgare L.). Dewatered biosolids fraction and Zn, Cd, and Pb concentrations in soybean [320-350 g kg Ϫ1 dry matter (DM)] were alkaline stabilized by mixing [Glycine max (L.) Merr.] plants. Sloan and Basta (1995) them with cement kiln dust and composting aerobically. The product reported that N-viro soil effectively remediated soil had some liming value (300 g kg Ϫ1 DM CaCO 3 equivalent on average) acidity and Al toxicity in three highly acidic soils. Wong and contained an average of 7.2, 2.3, and 19.5 g kg Ϫ1 DM of N, P, (1995) showed that mixtures of alkaline fly ash and and K. Two field experiments compared the P or K value of the biosolids mixed with loam soil decreased the availability biosolids with inorganic fertilizer P or K for seven consecutive annual spring barley crops on two contrasting soils. All biosolid and fertilizer of Zn, Cu, and Cd to tall wheatgrass [Elytrigia elongata treatments gave higher yields than the controls. Biosolids gave higher (Host) Nevski] plants in a pot experiment and increased grain and straw yields than fertilizer P, similar grain and straw yields plant yield. In contrast, Sajwan et al. (1995) found into fertilizer K, and higher grain weights and more grains per ear than creased concentrations of Cu and Zn in sorghum/sufertilizer P or K. These effects may have been due to, inter alia, dangrass hybrid plants in a loamy sand amended with higher soil pH and S inputs. An increasing soil pH from biosolid a mixture of coal fly ash and sewage biosolids. One application was associated with lower shoot Mn concentrations, but problem with using coal fly ash is its relatively high no Mn deficiency symptoms were observed. Alkaline biosolids acted concentration of B. Relatively low concentrations of B as a slow-release P fertilizer, and biosolid P was at least as availablecan be phytotoxic, especially to cereals, and B may affect to the crops as inorganic fertilizer P. Biosolid K was also as available as fertilizer K. A calculation of nutrient balances indicated that current plant growth when high application rates of biosolids fertilizer P recommendations could be lowered. P. Christie, Agric. and Environ. Sci. Division, Dep. of Agric. and for agricultural use by using rural batches of sewage Rural Dev. for N. Ireland, Newforge Lane, Belfast, United Kingdom biosolids with lower metal loadings than urban or indus-

SummaryExperiments were carried out to determine the tensile properties of mature wheat roots and the force necessary to pull roots from undisturbed soils at a range of moisture contents using an Instron materials testing rig. Roots decreased in cross sectional area from 1.5 to 0.1 mm2and in tensile strength from 7.0 to 2.3 Newtons (N) along the first 12 cm of their length. Breaking strain was constant along the root but the breaking stress increased. Increased seeding rate decreased root diameter and tensile strength but plant growth regulators and fertiliser nitrogen level did not affect the tensile properties. Roots were pulled from mesh tubes of soil (25 mm ± 75 mm) into which they had grown. The peak loads for sandy clay loam and sandy loam soils were 4.8 and 3.9 N respectively and increasing the soil moisture from 17% to 26% reduced the peak load from 5.2 N to 3.5 N. With the drier soil the inner stele pulled free leaving the outer periderm in the soil in a higher proportion of the roots indicating a stronger root/soil bond than in the wetter soil. The load us displacement relationship when pulling roots from soil resembled that for a fibre reinforced composite material. The presence of branch roots resulted in an uneven trace in which there were a number of sub‐peaks as branch roots gave way. It is suggested that soil wetting could contribute to lodging of wheat by reducing the resistance of roots to slippage and breaking.