Since many soils used for growing potatoes in the UK are likely to be close to their plastic limit for cultivation during early spring, there exists the potential for soil compaction to occur during planting which will restrict root penetration. A series of experiments showed that soil compaction delayed emergence, reduced rate of leaf appearance and ground cover expansion, shortened canopy cover duration and restricted light interception, which combined to reduce tuber yield. Rooting density and maximum depth of rooting were reduced, particularly where compaction was shallow. In some soils, irrigation helped alleviate some of the effects of compaction but in others it exacerbated their severity. Using a cone penetrometer, relationships between rate of root penetration and soil resistance (Ω) were established from a number of experiments and replicated blocks in commercial fields and an overall relationship of the form y=16·3–4·08Ω mm/day was produced. Root penetration rates of c. 20 mm/day were measured in the intensively-cultivated ridge zone but growth rates were halved at a Ω of 1·5 MPa. A survey of 602 commercial fields showed that two thirds of fields had Ωs ⩾3 MPa (where root growth rates would be <2 mm/day) within the top 0·55 m of the soil profile. Thus, rooting depth is likely to be considerably shallower than desirable and lead to inefficiency of water and nutrient utilization. The use of powered cultivators to separate stones and clods from beds or ridges and produce a fine seedbed is now almost universally adopted in the UK. However, the system is both time and energy inefficient and increases the risk of creating soil compaction, particularly at shallow depths. All cultivation equipment has been shown to cause compaction and it is suggested that the consequences of the shortening of the growing season from delaying planting by a few days to allow the soil to dry are far less than the yield and quality losses caused by compaction.

Four experiments conducted over three seasons (2002–05) at the Crops Research Unit, University of Reading, investigated effects of canopy management of autumn sown oilseed rape (Brassica napus L. ssp. oleifera var. biennis (DC.) Metzg.) on competition with grass weeds. Emphasis was placed on the effect of the crop on the weeds.

Rape canopy size was manipulated using sowing date, seed rate and the application of autumn fertilizer. Lolium multiflorum Lam., L.×boucheanum Kunth and Alopecurus myosuroides Huds. were sown as indicative grass weeds.

The effects of sowing date, seed rate and autumn nitrogen on crop competitive ability were correlated with rape biomass and fractional interception of photosynthetically active radiation (PAR) by the rape floral layer, to the extent that by spring there was good evidence of crop: weed replacement.

An increase in seed rate up to the highest plant densities tested increased both rape biomass and competitiveness, e.g. in 2002/3, L. multiflorum head density was reduced from 539 to 245 heads/m2 and spikelet density from 13 170 to 5960 spikelets/m2 when rape plant density was increased from 16 to 81 plants/m2. Spikelets/head of Lolium spp. was little affected by rape seed rate, but the length of heads of A. myosuroides was reduced by 9% when plant density was increased from 29–51 plants/m2.

Autumn nitrogen increased rape biomass and reduced L. multiflorum head density (415 and 336 heads/m2 without and with autumn nitrogen, respectively) and spikelet density (9990 and 8220 spikelets/m2 without and with autumn nitrogen, respectively). The number of spikelets/head was not significantly affected by autumn nitrogen.

Early sowing could increase biomass and competitiveness, but poor crop establishment sometimes overrode the effect. Where crop and weed establishment was similar for both sowing dates, a 2-week delay (i.e. early September to mid-September) increased L. multiflorum head density from 226 to 633 heads/m2 and spikelet density from 5780 to 15 060 spikelets/m2.

Three experiments conducted over two years (2002–04) at the Crops Research Unit, University of Reading, investigated competition between autumn sown oilseed rape cultivars (Brassica napus L. ssp. oleifera var. biennis (DC.) Metzg.) and Lolium multiflorum Lam., L.×boucheanum Kunth and Alopecurus myosuroides Huds., sown as indicative grass weeds.

Rape cultivar (cv.) had a substantial effect on grass weed seed return. Over the six cultivars tested, L. multiflorum spikelet production ranged from just under 400 spikelets/m2 in the presence of cv. Winner to nearly 5800 in competition with cv. Lutin. Cultivar competitiveness was associated with high biomass, large dense floral layers and early stem extension. There was some evidence of differential competitive tolerance between rape cultivars.

The results suggested that rape cultivars could be screened for competitiveness by measuring floral layer interception of photosynthetic active radiation.

L.×boucheanum cultivars varied in ability to compete with rape. In the absence of inter-specific competition, spikelet density was similar for Aberecho and Polly (circa 31 000 spikelets/m2) but when grown with rape Polly outyielded Aberecho (i.e. 12 090 and 7990 spikelets/m2 respectively).

The objective of the present study was to determine the optimum plant density of four pigeonpea genotypes, representing early, medium and late maturing types, grown in five contrasting environments in Tanzania. ICPL 86005 (early), Kat 50/3 and QP 37 (medium) and Local (late) were grown at four plant densities (40 000–320 000 plants/ha) in irrigated and rainfed conditions at Ilonga and under rainfed conditions at Kibaha, Selian and Ismani. At maturity, total above-ground biomass and seed yield (SY) were measured. The highest yields were obtained in the irrigated experiment at Ilonga, where the medium/late genotypes produced 25 t biomass/ha and 5·6 t seed/ha. The lowest SY were at Kibaha, 0·58 to 1·76 t/ha, where a severe drought occurred. In nearly all cases the response to density was linear or asymptotic. The response of ICPL 86005 was significantly different from the other three genotypes. The optimum density for SY varied from 37 000 to 227 000 plants/ha in ICPL 86005, compared with 3000 to 101 000 plants/ha in the medium/late genotypes. The highest optimum density was at Selian and Ismani and the lowest at Ilonga and Kibaha, where drought occurred. Optimum densities therefore varied greatly with genotype (duration) and environment, and this variation needs to be considered when planning trials.

Ethiopian mustard (Brassica carinata) genotypes with different contents of oleic acid (C18:1) in the seed oil could be useful for food and industrial applications. The objectives of the present research were to study the inheritance of high C18:1 in the seed oil of different lines of Ethiopian mustard and its relationship with erucic acid content (C22:1). The low C18:1/high C22:1 mutant line L-1806, the high C18:1/high C22:1 mutant line L-482, the high C18:1/low C22:1 mutant line L-2890 and the low C18:1/very high C22:1 mutant line L-1630 were isolated after a chemical mutagen treatment of C-101 seeds (about 94 g C18:1/kg and 450 g C22:1/kg). The high C18:1/zero C22:1 line L-25X-1 was obtained by interspecific crosses of Ethiopian mustard with rapeseed and Indian mustard. Plants of lines L-2890×C-101, L-482×L-2890, L-1630×L-25X-1, L-1630×L-2890 and L-482×L-1806 were reciprocally crossed and F2 and the BC1F1 generations were obtained. Cytoplasmic effects were not observed in any of the crosses. The segregation pattern in F2 and BC1F1 populations differed in the crosses studied. The inheritance of C18:1 content in crosses segregating for this fatty acid was that expected for one (crosses between L-482×L-1806), two (L-2890×C-101) or three (L-1630×L-2890, L-1630×L-25X-1 and L-482×2890) loci. Oleic acid segregation indicated control of accumulation by two segregating genetic systems, one acting on chain elongation from C18:1 to C22:1 and the other involving desaturation from C18:1 to linoleic acid (C18:2). Accumulations of C18:1 and C22:1 were influenced by the same loci (M1, M2, E1 and E2), which control the chain elongation steps leading from C18:1 to C22:1. In addition, C18:1 was influenced by one additional locus (tentatively named OL) involved in control of desaturation of C18:1 to form C18:2. The genetic constitution of the parent lines would be OlOlE1E1E2E2m1m1m2m2 for L-2890, OlOlE1E1E2E2M1M1M2M2 for C-101, ololE1E1E2E2M1M1M2M2 for L-1630, OlOle1e1e2e2M1M1M2M2 for L-25X-1, ol1ol1E1E1E2E2M1M1M2M2 for L-482 and Ol1Ol1E1E1E2E2M1M1M2M2 for L-1806. Transgressive recombinants were obtained from the cross L-1630×L-25X-1, with about three-fold increase of the C18:1 content of the parents (>643 g/kg) and free of C22:1 content, which represent a high potential for commercial exploitation.

Since the 1970s, the delivered sugar yield per hectare has risen at an average annual rate of 0·111 t/ha, while the sugar yield in the official variety trials has increased at an average annual rate of 0·204 t/ha. These increases are usually considered to be the result of improvements in varieties and in beet agronomy. The present paper considers the possible impact of recent changes in climate on UK sugar yields by using the Broom's Barn Crop Growth Model and daily weather data collected over the last 30 years. Simulations of sugar yield using weather in eastern England since 1976 increased by an average annual rate of 0·139 t/ha, which accounted for about two thirds of the rate in the official variety trials. This increase was not an artefact of the accuracy of weather recording but it was, in part, accounted for by the trend to earlier sowing. Although it was not statistically significant, the earlier sowing trend was associated with an increase of 0·025 t/ha per year and was an indirect effect of the climate change. The annual deviations from these trends have not tended to become significantly bigger or smaller over the three decades. The model is not variety-specific, so it makes no allowance for variety improvements during the last 30 years. Clearly, varieties have improved so the implication must be that some of the changes in agronomy have tended to decrease the yields significantly. The changes in agronomic practice most likely to be responsible are the extension of the crop processing campaign, leading to greater post-harvest storage losses, and a decrease in the irrigated area.

Sugar beet (Beta vulgaris L.) is one of the most important sugar crops worldwide. Despite the fact that sugar beet crop has high requirements for boron (B), the effect of B applications on seed yield and on seed quality is not known. A 2-year field study was conducted to determine whether soil and foliar B applications during anthesis increase seed set, final seed yield and improve seed quality of sugar beets. Boron solutions were applied at four rates (0, 245, 490 and 735 mg/l of B) as foliar applications and at two rates (1·5 and 3 kg/ha of B) as soil applications to field plots exhibiting no vegetative symptoms of B deficiency. Foliar B application increased the concentration of B in vegetative and reproductive tissues much more than soil application. In addition, foliar B application increased the seed yield by an average of 10% in the first year and by an average of 44% in the second year. The mean seed weight was affected by B application as it was increased in both years. The proportion of larger seeds (>5·00 and 4·5–5·00 mm) increased with increasing application of B. Moreover, seed quality was affected and the proportion of abnormal seedlings was decreased with B application. However, seed vigour was not affected by B application. These data indicate that foliar B application can improve seed yield and seed quality of sugar beet grown for seed production. However, the physiological basis of this effect remains unknown.

Animal manures are a valuable resource, providing readily available plant nutrients; however, runoff from lands receiving animal manure has been shown to contribute to water pollution. Understanding the loss of nutrients from slow release fertilizers, such as animal manure, after application is critical in determining and designing practices to reduce and/or control the temporal availability and potential offsite transport of NO3-N and NH4-N after application. A block study was designed to compare and contrast the temporal losses of NO3-N and NH4-N from three slow release fertilizers (sulphur-coated urea, composted dairy manure, and poultry litter) and one fast release fertilizer (ammonium nitrate) applied to bermudagrass (Cynodon dactylon L. Pers.) turf. Cumulative NO3-N loss from plots receiving application of the manufactured (NH4NO3 and sulphur-coated urea) products was significantly (P<0·05) greater than the measured losses from plots receiving application of natural products (composted dairy manure and poultry litter). The cumulative NO3-N recovered in the runoff expressed as a proportion of applied N was 0·37 for ammonium nitrate, 0·25 for sulphur-coated urea, 0·10 for composted dairy manure, and 0·07 for poultry litter during the 10-week study period. Cumulative NH4-N recovery fractions were an order of magnitude less than the cumulative NO3-N fractions and no significant differences (P>0·05) were measured across treatments. Significant differences (P<0·05) in NH4-N and NO3-N loss through time were measured for the four treatments. The findings of the present study indicate that land-applied animal manures are less susceptible to initial losses of N when compared to manufactured fertilizers.

Fifteen indigenous nondescript kids (8·2 kg; 8 months initial age), randomly allotted into three equal groups, were used to study the effects of supplementation of extra iodine on their performance when fed a leucaena (Leucaena leucocephala) leaf meal containing diet. Group I (CON) was fed a control concentrate supplement consisting of a conventional protein source whereas the other two groups (LL and LLI) were fed a concentrate containing leucaena leaf meal so as to supply 0·5 of the net crude protein (CP) requirements. Additionally, animals in group LLI were given supplemental iodine (as potassium iodide solution) at 0·25 mg/head/day. Wheat straw was provided ad libitum as the sole source of roughage during the 120 days of the experimental period. A metabolism trial, conducted at the end of the feeding trial, revealed no variation in the dry matter intake (DMI) among the groups. A significant (P<0·01) decline was evident in digestibility of CP in both the leucaena-fed groups (0·463 and 0·482 versus 0·586) whilst that of the other organic components remained unaffected. Animals on the LL diet exhibited lower (P<0·01) nitrogen retention and average daily gain (ADG) in live weight (LW). Blood collected periodically was analysed for the thyroid hormones triiodothyronine (T3) and thyroxine (T4) as well as other biochemical parameters. At the end of the experimental feeding, the cell-mediated immune (CMI) response of the goats was assessed by intra-dermal inoculation of phytohaemagglutinin-P and measuring the change in skin thickness at various post-inoculation hours. The results revealed that the serum concentration of glucose was significantly (P<0·05) higher in the LLI group of animals fed leucaena with iodine. The concentration of cholesterol in serum of LL animals increased significantly (P<0·05) compared to the CON and LLI groups. No variation due to dietary interventions was evident in other indices of metabolic profile. While the concentration of circulating T3 remained unaffected due to dietary intervention, that of T4 reduced significantly (P<0·05) in the LL group. Moreover, the T4 concentration in the LLI group remained similar to that of control indicative of positive impact of iodine supplementation. The immune response revealed that the skin thickness of animals in the LL group was lower (P<0·05) as compared to the control, indicating a compromise of CMI response due to feeding of leucaena leaf meal. Supplementation of iodine appeared to be partially effective in potentiating the response. In conclusion, iodine supplementation could be adopted as a strategic management strategy to ameliorate the negative impacts of feeding leucaena leaf meal in growing kids.

Four Karan/Friesian crossbred (Holstein×Tharparkar) dairy cows in late lactation (>200 days) were fed a basic diet of green maize and concentrates with an increasing proportion of Leucaena leucocephala (leucaena) leaf meal (LLM). The proportion was gradually increased from 0·25 of the dry matter intake (DMI) in the first week to 0·50 in the second, 0·75 in the third and ad libitum in the fourth week. Mimosine, 3,4-dihydroxy pyridine (3,4-DHP) and 2,3-dihydroxy pyridone (2,3-DHP) levels were determined in milk, serum, urine and faecal samples. On average DMI of leucaena was 0·023–0·025, 0·025–0·027, 0·027–0·028 and 0·022–0·025 of live weight (LW) during the first, second, third and fourth week, respectively. Mimosine, 3,4-DHP and 2,3-DHP appeared in the blood serum during leucaena feeding and continued appearing up to sixth week of experimental feeding even after the withdrawal of leucaena from the 34th day onwards. Similarly, excretion of mimosine, 3,4-DHP and 2,3-DHP were observed even after withdrawal of leucaena from the diet. The feeding of LLM resulted in a reduced level of T3 (Triiodothyronine) and T4 (Thyroxine) within a week of LLM feeding. The level of T3 and T4 improved to normal after withdrawal of LLM from the diet. The serum aspartate transferase (AST) and serum alanine transferase (ALT) activities were within the normal range. Leucaena feeding improved milk yield and composition only up to 3 weeks of feeding. The concentration of mimosine, 3,4-DHP and 2,3-DHP in milk was 0·33, 0·05 and 0·02 that of blood, respectively. The secretion of mimosine, 3,4-DHP and 2,3-DHP in the milk might be a concern for health of the offspring of leucaena-fed animals as well as human beings consuming such milk.