Mixtures of annual weeds emerging 1 week after and competing all season with potatoes (Solanum tuberosum L.) reduced tuber yields by an average of 54% compared to 16% in comparable treatments in which weeds emerged 3 weeks after potatoes. Weeds reduced tuber yields 19% 8 weeks after potatoes emerged and 25 to 45% 10 weeks after emergence. After full-season competition, for each additional 10% of the total dry biomass represented by weeds, there was a decrease of 12% in fresh tuber yield. This relationship was not valid if potatoes were harvested early, which reduced the deleterious effect of weeds on potato yields. Weed competition reduced both size and number of tubers, but had little effect on specific gravity of tubers. In some instances, the reduction in tuber size by weeds reduced the percentage of tubers that were marketable.

The response of 22 potato (Solanum tuberosum L.) cultivars to soil-incorporated and foliar applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one] at rates of 0.5 and 1.0 kg ai/ha, was evaluated in field experiments from 1979 to 1982. Metribuzin significantly reduced the yield of marketable tubers in several potato cultivars. Foliar applications generally resulted in more injury than soil applications. Yields were reduced primarily through stand reduction and a decreased number of tubers per plant. Neither tuber size nor specific gravity of tubers was significantly reduced in the cultivars studied. The most susceptible cultivar was ‘Alaska Red’, followed by ‘Rhine Red’, F72117, ‘Caribe’, and ‘Shepody’. Other cultivars evaluated were highly tolerant to metribuzin, irrespective of rate or method of application. There was an increase in hollow heart in cultivars ‘Atlantic’ and ‘Lemhi Russet’ following treatment with metribuzin.

The effects of metribuzin herbicide and phorate insecticide were studied on summer harvest chipping-potatoes at Muscatine, IA, from 1989 to 1991. Phorate at 1.5 kg/ha increased total and ‘A’-size tuber yield and tuber specific gravity. Metribuzin applied at 0.56 kg/ha postemergence decreased total and ‘A’-size tuber yield. Metribuzin applied at 0.56 kg/ha preemergence and 0.28 kg/ha postemergence did not reduce Atlantic cultivar yield. Metribuzin did not affect ‘B’-size tuber yield or specific gravity. Phorate in combination with metribuzin did not increase plant injury or reduce tuber yield.

Twenty-four lactating Holstein dairy cows (12 first lactation and 12 multiparous; day in milk = 11 ± 5 days) were allotted to a randomised complete block design in a 2 × 3 factorial with four replicates per treatment to evaluate the effects of two methods of alfalfa feeding (dry and reconstituted to achieve a theoretical dry matter (DM) content of 350 g/kg) and three geometric mean (GM) particle sizes of alfalfa (9.13, 4.51 and 1.20 mm) on performance of dairy cows for a period of 28 days. Diets were offered for ad libitum intake as total mixed rations (TMR). The GM particle size, its standard deviation, and the values of physical effectiveness factor of alfalfa and TMR decreased as alfalfa particle size decreased. Reduction of particle size and reconstitution of alfalfa increased the bulk density and the functional specific gravity of alfalfa and rations. Reduction of particle size decreased insoluble dry matter, water-holding capacity, and hydration rate of alfalfa. As particle size decreased, the amount of physically effective NDF in the ration (g/kg) decreased but the daily intake of physically effective NDF (kg/day) increased. Reduction of particle size and reconstitution increased dry matter intake (DMI) and ruminal passage rate, but reduced NDF and ash digestibilities, ruminal pH, N-NH3, milk fat, total chewing activity, rumination and eating time, total and ruminal mean retention time, and time delay of marker. Increased functional specific gravity, from reduced forage particle size and the reconstitution of alfalfa, was the most important factor influencing DMI, milk composition, and chewing activity.

Plastic particles of defined length (2, 5 mm) and specific gravity (sp.gr. 1.10, 1.34, 1.77) were administered just before feeding into the reticulo-rumen of four cattle and four swamp buffaloes given a diet predominantly of rice straw ad lib. Simultaneously, doses of ground rice straw marked with Cr and Yb were likewise given. Plastic particles were recovered from faeces for 12 d after dosing, and divided into non-ruminated (NR) and ruminated (R) particles. Excretion data of plastic particles were interpreted using a four-pool model incorporating passage of NR (kp) and R from the reticulo-rumen, post-ruminal passage, rate of chewing (kr) and two lag times. An inverse relationship was found between kr and sp.gr. The kr was higher for 5 mm than that for 2 mm particles. In contrast, kp was greatest for particles of sp.gr. 1.34, with higher kp for 2 mm than for 5 mm particles. Rates of passage and rumination (kp, kr) were higher for buffaloes than for cattle. Rumination time was related to kr, most highly (r2 0.96) with kr of 2 mm, 1.10 sp.gr. particles. Fragmentation of 5 mm particles by rumination tended to increase the rate of passage from the rumen. Ruminal passage rates of Yb and Cr markers were poorly correlated with each other and with kp of any of the plastic markers. Reanalysis of published data from plastic particle studies supported the relationships between sp.gr., size, kp and kr. In view of the additional information (kr) obtained using plastic particles, we suggest their use may be appropriate in studies which investigate specific differences in digestive function, while being less suitable for investigating differences between diets.