Twenty-two field experiments in England, done between 1986 and 2000, tested the effects of phosphorus (P) fertilizers on number of tubers and tuber yield in Solanum tuberosum. Applying P fertilizer resulted in statistically significant increases in tuber yield in six experiments and the optimal P application rate ranged from c. 90 to 180 kg P/ha. Statistically significant increases in yield in response to application of P fertilizers were found only in soils that contained < 26 mg Olsen-P/l (< Index 3) and appeared to be associated with increases in ground cover. Statistically significant increases in the number of tubers in response to application of P fertilizer were found only in soils that contained < 16 mg Olsen-P/l (< Index 2) and appeared to be associated with an increase in ground cover by the time of tuber initiation (c. 5–6 week after planting). Each tonne of tuber fresh-weight yield was, on average, associated with removal of 0·39 kg P but regression analysis showed that this value increased as soil Olsen-P increased. Re-analysis of published data showed that whilst the probability of a response to P fertilizer and the optimum P application rate may have been overestimated, some statistically significant responses to P fertilizer did occur when Olsen-P was > 26 mg/l. The absence of yield responses on P Index 3 soils found in the current experiments was attributed to increased use of irrigation that may have increased the availability of soil P. Re-interpretation of data from long-term experiments showed that the agronomic benefits of increasing soil P status by applying more P than is removed by harvested crop parts, are small. Since large P residues, estimated by Olsen-P or degree of soil P saturation, are associated with desorption of P and consequent loss to drainage water it is inadvisable to increase soil P above Index 3. For these reasons, no P fertilizer is recommended for Index 4 soils, an amount equivalent to replacement is recommended for Index 3 soils but up to 110–130 kg P/ha should be applied to Index 0 soils. Applications of foliar P had no effect on number of tubers or tuber yield and this practice cannot be recommended.

Between 1995 and 1999, eight response experiments tested the effects of magnesium (Mg) fertilizers on the yield of potato crops grown in East Anglia, the Midlands, the West and Southwest of England. In addition, a further six experiments tested the effects of varying nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca) supply on the tuber concentrations and uptake of Mg by potato crops. The experiments were done on soils that contained varying amounts of exchangeable Mg and K but were still typical of soils used for potato production.

In the eight response experiments, use of Mg fertilizer had no effect on total tuber fresh weight yield even though yields were often much larger than the national average yield. Increasing the N supply to the crop was often associated with an increase in the concentration of Mg in leaves and stems. This may have been due to N facilitating Mg uptake or a consequence of N delaying canopy senescence and, thus, delaying the translocation of Mg from haulm to tubers. Compared with the effects of N, varying the Mg and K supply to the crop had small and inconsistent effects on crop Mg uptake. Since the experiments also showed that Ca supply and soil K[ratio ]Mg ratio had no effect on crop yield and erratic effects on tissue Mg concentration, fertilizer recommendation systems based on ratios of nutrients in the soil cannot be endorsed. When these current experiments and older, published experiments are taken into account there is little justification for applying Mg fertilizer to soils with Mg Indices > 0 and on soils with Mg Index 0 an application of c. 50 kg Mg/ha would be sufficient.

The genic male-sterile rice (GMSR) sensitive to photoperiod during the panicle development period is a novel type of germplasm in rice, which is sterile under the long-day condition but fertile under the short-day condition. The fertility is also affected by temperature. A number of GMSR lines have been popularly used in commercial seed production of hybrid rice in China. Because the sterility is decided by environmental factors, a set of fertility conversion indices has been proposed to evaluate the usability and to determine the suitable regions for safe application of these male sterile lines. In the present experiment, 13 photoperiod-sensitive (PGMSR) lines that are dominant in China were sown by stages in the field at Hainan Island (18° 14′ N), Quiyang (26° 35′ N) and Wuhan (30° 38′ N) in China. The fertility and sterility were distinguished on the percentage of seed-setting on the bagged panicles (PBS). The fertility conversion indices were determined on the day-length and temperature regimes and on a fertility quantifying model, and comparison was made between the two methods. Results showed that it was feasible to determine the fertility conversion index of GMSR lines based on data of bagged seed-setting rates in experiments of sowing at different times in the field. Of the 13 sterile lines observed, two of the PGMSR were found to be completely sterile when the length of the day exceeded 12·3 h. Five temperature-sensitive (TGMSR) lines had fertility conversion indices of 24 °C. One of the photoperiod- and temperature-sensitive (PTGMSR) lines showed that steady fertility conversion occurred under the short day in spite of high or low temperature. These GMSR lines are adaptable to the conditions of day-length and temperature in the main rice-growing regions of China and thus of high value in application to seed production.

The effects of five stake weights (50, 63, 75, 88 and 100 g) of three cassava cultivars (TMS 30572, TMS 91934 and NR 8083) on the growth and yield of cassava were studied for 2 years (1992/93 and 1993/94) in Nigeria. The leaf area index (LAI), crop growth rate (CGR), net assimilation rate (NAR), leaf area duration (LAD), harvest yield and harvest index (HI) were dependent on the weight of stake planted and were greatest at the stake weight of 88 g (875 kg/ha) irrespective of cassava cultivar. Variations in LAI, LAD and HI of stake weights between 75 and 100 g were non-significant. The profusely branching cassava cultivars, TMS 30572 and NR 8083, achieved greater LAI, CGR, NAR and LAD relative to the sparsely branching cultivar, TMS 91934. The significant growth and yield differences among the stake weights with the optimum at a stake weight of 88 g (875 kg/ha) indicates the need to adopt this stake weight for sustainable and improved growth and yield in cassava production.

Incomplete block (IB) analysis of lentil yield trials in lattice block designs substantially reduced experimental error variability compared to randomized complete block (RCB) analysis. Spatial variability, which may exist in two dimensions in the field, can be modelled using various alternative covariance structures for the plot errors. To investigate the adequacy of the incomplete block analysis, we fitted a first order autocorrelation error structure (AR1) in both the column direction and the row direction after allowing for the variance model of the lattice design. We also considered random splines in columns. The best model was selected on the basis of the residual deviance of each of the 53 trials we examined. Gains in efficiency (over RCB) for pair-wise comparison of genotypes and selection gains were obtained for the selected models and for the lattice blocks (considered as a control model). Spatial models where the plot error was modelled as AR1 in columns or as AR1×AR1 in rows and columns after allowing for random effects of lattice blocks were most frequently selected. Models with spatial errors were found best in 74% of the trials when used with random effects of lattice block and in the remaining trials when used without lattice blocks. The average gain in efficiency over RCB analysis by using the best models at the analysis stage was around 50%. The best models were also, on average, more efficient than the lattice model. Expected average genetic gain due to selection of the top five lines was approximately 20% for the best models. The predicted genotype means showed less change in rank when comparing RCB with lattice analysis than when comparing RCB with the best method. Use of spatial models resulted in different genotypes being selected, giving a higher genetic advance. Since the use of spatial models requires only a change in computation together with knowledge of the field layout, the use of spatial methods together with good experimental design is recommended as a cost-effective method for achieving improved genetic progress.

The possibility of increasing seed yield in chickpeas was studied by changing sowing time from spring to autumn in an experiment conducted in central Greece over 4 years. Six chickpea varieties, two susceptible to Ascochyta blight and Sclerotinia diseases and four resistant, were evaluated in two sowing seasons (autumn and spring).

Results showed that autumn sowing in comparison with spring influenced reproductive and growth periods of the varieties as follows: advanced initiation of flowering (April instead of May), increased flowering duration of the varieties from 7 to 13 days and advanced time for harvest, on average up to 4 days when an exceptionally rainy spring prevailed and up to 30 days when exceptionally dry. Due to the above changes induced by autumn sowing, varieties yielded on average from 23–188% (655–1015 kg/ha) more than if they were sown in spring. The largest per cent increase was observed during the year with the driest spring and the smallest during the year with the wettest spring. The two susceptible varieties ‘Thiva’ and ‘Gravia’ when infected by Ascochyta blight and Sclerotinia diseases in autumn sowing, had yields similar to the spring sowing. However, during the years without infection these two varieties yielded more in autumn sowing.

Cotton (Gossypium hirsutum L.) yield and quality is affected by altered fruiting patterns with progress in season. The present study was conducted to analyse normal and altered (abnormal) boll (fruit) development at maturation phase. Both normal and abnormal bolls of the same age groups were analysed for growth in terms of dry weight, water content and endogenous abscisic acid (ABA) content of fibre and seed. Endogenous level of ABA was estimated by using antibodies raised against ABA–protein conjugate. To amplify the reaction, indirect ELISA (Enzyme Linked Immuno Sorbent Assay) was performed. A marked decrease in dry matter accumulation (DMA) of seed and fibre was observed in abnormal bolls as the season progressed. Fibre from the abnormal bolls showed marked variation in endogenous ABA content, however, in abnormal seeds water content and endogenous abscisic acid content showed significant variation compared to that of normal bolls. From the results, it is concluded that a marked decrease in seed dry weight may be because of a decrease in water content and accumulation of higher endogenous abscisic acid content, whereas, the major reason for reduced fibre weight may be due to accumulation of endogenous abscisic acid.

The tropical perennial clover, T. semipilosum, and the species, T. repens, exhibited both similarities and differences in their nodulation characteristics following Rhizobium inoculation. Both T. semipilosum and T. repens were infected via root hairs, formed indeterminate nodules and commenced active nitrogen-fixation approximately 1 week after inoculation. Effective Rhizobium strains produced on average four nitrogen-fixing nodules per T. semipilosum plant, predominantly in the upper region of the tap root. In contrast, 65% of the average 15 nodules per T. repens plant were induced on lateral roots. The Rhizobium strain-ANU843, effective (Nod+Fix+) on T. repens, caused root hair branching and twisting on T. semipilosum, although plants did not fix nitrogen, indicative of an ineffective host–strain interaction. Such ineffective interactions were associated with increased total numbers of nodule-like structures on T. semipilosum; these nodules were atypically associated with, or in close proximity to, lateral roots. Using a GUS gene-modified rhizobia to monitor nodule occupancy, a third of the total nodule-like structures formed from the incompatible interactions showed a positive GUS reaction, indicating that colonization by Rhizobium strains of some of the nodule-like structures had occurred. Moreover, about 70% of the GUS positive nodule-like structures from the incompatible interactions were localized at the junction between the tap and lateral roots. These observations are consistent with an atypical infection route by the incompatible strains.

It has been previously shown in this laboratory that feeding a model condensed tannin, quebracho tannin, reduces the small intestinal nematode burden in sheep and rats. The aim of the current programme was to determine whether this occurs through direct toxicity against the parasites. Both in vivo and in vitro studies were conducted. The first study compared the effect of dietary quebracho tannin (40 g/kg) on the establishment of the parasitic nematodes Nippostrongylus brasiliensis and Trichinella spiralis in the rat small intestine. The burden of N. brasiliensis, which, although closely associated with the mucosa, actually dwells within the small intestinal lumen, was significantly reduced (P<0·001) by dietary quebracho tannin. In contrast, T. spiralis, which penetrates into the small intestinal mucosa, was unaffected (>0·05) by the dietary inclusion of quebracho tannin. The second study involved monitoring the survival of adult N. brasiliensis and T. spiralis when incubated in vitro in varying concentrations of quebracho tannin in Hanks’ balanced salt solution. The survival of N. brasiliensis was compromised at concentrations as low as 0·01% (w/v) quebracho tannin but improved with the addition of 0·1% (w/v) polyethylene glycol, which binds to, and inactivates, tannin. T. spiralis was similarly affected, but much more rapidly. These results suggest that dietary quebracho tannin may reduce nematode worm burdens through a toxic effect that requires direct contact between parasite and tannin. This raises the possibility that feeding locally available plant material containing condensed tannins may be an alternative method for controlling parasite infections, especially in areas such as the tropics and subtropics.

Four steers, average body weight 260±15 kg, fitted with portal catheters were used in a 4×4 Latin Square design to evaluate the influence of dietary protein degradability in the rumen on peptide and amino acid fluxes across the gastrointestinal tract. Dietary protein degradability was regulated by using different protein sources and the diets were calculated to contain 130 g CP/kg and 9·62 MJ ME per kg DM. Plasma concentrations of amino acids were analysed before and after acid hydrolysis of samples first subjected to chemical deproteinization and physical ultrafiltration, and peptide amino acids (PAA) were calculated as the difference between total and free amino acids (FAA). Portal blood flow and arterial concentrations of FAA and PAA were not affected by protein degradability or by diet. Venoarterial concentration difference and net portal flux of FAA tended to increase (P < 0·10) with increase of degradable protein intake. Portal-arterial concentration difference (P < 0·05) and net portal flux (P < 0·10) of PAA increased linearly as dietary protein degradability increased. The proportion of PAA in total amino acid (FAA+PAA) net flux was not modified by dietary protein degradability or by diet, and the mean value as a proportion was 0·32. The major PAA absorbed were glutamate, leucine, aspartate and lysine for all diets, accounting in total for 0·50 of PAA flux. The results demonstrate that PAA may contribute significantly to AA flux across the portal-drained viscera (PDV) of steers, and both FAA and PAA net fluxes can be affected by degradable protein intake.