An account is given of large-scale trials of the use of saline water for the trickle irrigation of forest trees in the desert areas of Abu Dhabi, in eastern Arabia. Water of salinities up to an equivalent of 16,000 ppm have been used on Casuarine glauca and Eucalyptus camaldulensis. Growth rates ranged from 1.7 m in 7 years on salinities of 16,000 ppm to 10–12 m in 8 years on salinities of 2000–2500 ppm. Trickle irrigation appears to allow the use of more saline water than can be used with other systems, perhaps because plant roots are not subject to the fluctuations in moisture stress that occur under all other systems.

Soil phosphorus fractions, maize and cassava P uptakes in natural regrowth fallow and Pueraria phaseoloides fallow systems, as affected by the duration (1–3 years) of fallow, were assessed in 1998 and 1999 in a long-term fallow management trial, established in 1989 at the International Institute of Tropical Agriculture, Ibadan, Nigeria. After one and three years fallow respectively, the mean P accumulation in fallow vegetation was 4.2 and 9.4 kg ha−1 in 1998, and 8.9 and 12.1 kg ha−1 in 1999 for natural fallow. For Pueraria, the corresponding values were 6.3 and 7.4 kg ha−1 in 1998 and 6.1 and 13.5 kg ha−1 in 1999. The positive effects of fallow lengths on dry matter and P accumulation were not as pronounced under Pueraria. Continuous cropping reduced soil pH and depleted Olsen P more than crop-fallow rotations under both fallow systems. An increase in fallow duration enhanced the availability of resin P, NaHCO3-, and NaOH- extractable P fractions, especially under natural fallow. Continuous cropping in a natural fallow system resulted in lower resin inorganic P (Pi) and NaHCO3-extractable inorganic and organic P (Po) fractions, and higher refractory P fractions (concentrated HCl-extractable Pi and Po and residual P) as compared to crop-fallow rotations. Although continuous cropping in the Pueraria system resulted in higher refractory P fractions than the crop-fallow rotations, the effects of fallow length on P fractions were not consistent or pronounced. Maize and cassava P uptakes increased with fallow duration. Phosphorous in maize grain was positively correlated with fallow vegetation P accumulation. Total P uptake by maize was positively but weakly correlated with NaHCO3-Po, Olsen P and fallow vegetation P accumulation.

Experiments on okra to determine the economic loss caused by insect damage to the leaves or by harvesting young leaves as a vegetable are described. Leaf harvests at 1-weekly intervals yielded 30-50% more fresh leaf than harvests at 2 or 3-weekly intervals. Removing a quarter of each leaf or single leaves from the upper or lower parts of the plant at 3-weekly intervals did not affect marketable fruit yield, but yield was reduced by about 30% when one young leaf was harvested at 1 or 2-weekly intervals or when two or three leaves were harvested at S-weekly intervals. Removing more than one quarter of each leaf or two or three fully expanded leaves from the lower three-quarters of the plant at 3-weekly intervals also caused up to 40% yield loss.Harvesting single leaves at S-weekly intervals is therefore recommended if okra is to be grown for both leaves and pods. The plant can tolerate at least 25% defoliation, as can happen with insect damage, before any yield loss occurs.

F. O. Olasantan: Efecto de la deshojadura sobre el crecimiento y rendimiento del gombo (Abelmoschus esculentus,) y su importancia para modelos de cosecha de hojas y dano causado porplagas.

Clearing cotton stalks after picking is enforced by law in the Sudan to stop the spread of black-arm and leaf curl diseases. The magnitude of pull and lift requirements to uproot a single plant are important parameters in designing an efficient stalk-pulling machine. With the help of a specially built apparatus, 186 plants selected at random were uprooted and measurements of the magnitude of pull and plant lift were recorded. A magnitude of 121 kg pull, accompanied by a short lift of 4·9 cm, were found necessary to loosen all plants completely. Investigations have also included the percentage of plants pulled and their root dimensions in relation to the yield point.

The objective of this study was to elucidate the physiological basis of the significant yield decline that occurs during the fourth year of the pruning cycle of tea. Biomass partitioning, which was hypothesized to be a major factor in causing this yield decline, was measured by destructive harvests of entire tea bushes, in two contrasting, mature, field-grown tea cultivars (TRI 2025 and DT1) at the end of different years of the pruning cycle. In both cultivars, yield showed continuous increases from year 1 to 3, followed by reductions of 44% and 35% in TRI2025 and DT1 respectively in the fourth year. Patterns of biomass partitioning to roots, stems or branches did not correlate with the above yield variation whereas harvest index, canopy leaf area index and mature leaf dry weight showed variations which paralleled the yield variation. The fourth-year decline in harvest index was brought about by reductions in both shoot number per m2 and mean individual shoot weight, which indicate a reduction in sink strength. Both cultivars showed reductions in light-saturated photosynthetic rate of maintenance foliage during the second half of the pruning cycle, indicating reduced source capacity. Hence, a combined reduction of both sink strength and source capacity during the fourth year could have brought about the significant yield reduction in tea. A significant increase of root starch in the fourth year indicated a down-regulation of physiological activities of the bush towards the end of the pruning cycle. Mechanisms responsible for this down-regulation need to be elucidated by further research.

Cropping systems in the lowlands of temperate South America have been based on irrigated rice and beef-cattle production. Plough-and-harrow is still the most used method to prepare the soil after a season of irrigated rice, but it causes high soil disturbance and is time- and energy-demanding. To improve the sustainability of a rice–soybean rotation system, we studied an alternative method for soil preparation based on a heavy knife-roller. This method was evaluated during three cropping seasons and compared to the plough-and-harrow, applied after the harvest of irrigated rice in a flat hydromorphic soil in south Brazil. In the subsequent summer, soybean was seeded using a no-tillage seeder. Observations on soybean establishment and grain yield demonstrated that the alternative method performed as well as the plough-based system. Benefits of the roller-based method were a 50% reduction in energy consumption for soil preparation, corresponding to a 22% increase in overall energy use-efficiency of soybean production. Labour time and greenhouse gas emissions for soil preparation were reduced with 29 and 55%, respectively. Next to these savings, the roller-based method can also be performed shortly after rice harvest, creating better opportunities for cover crops or pastures in between rice and soybean. In conclusion, the equivalent agronomic and superior sustainability performance makes the knife-roller method an appealing alternative for seedbed preparation after irrigated rice in lowland production systems.

Results from five years trials showed that irrigation was frequently needed to ensure early and adequate germination of cotton, that the use of a water balance to determine time and amount of irrigation was practical and economic, that there was no appreciable effect of fertilizer on yield of seed cotton on these soils, and that there was no significant change in the fertility of the soil after four crops of cotton.

At Ukiriguru, Western Tanzania, three experiments over 4 years investigated the effects of nitrogen (up to 240 kg. N/ha.) and phosphate (up to 50 kg. P/ha.) on a Cenchrus ciliaris pasture. Dry matter yield increased with up to 160 kg. N and dry matter content also increased with nitrogen, whereas crude protein contents were initially lowered and then increased by the higher rates of nitrogen. These differences are attributed to changes in the leaf/framework ratio. The crude protein yield increased with each nitrogen level. Sulphate of ammonia markedly lowered the soil pH. The only responses to phosphate were when it was cultivated into the top soil, when there was a small increase in yield and a fall in crude protein.

Effects of simulated and actual grazing at the tillering stage on tiller production and other agronomic characters were studied over a number of seasons at two sites in northern Syria with two local barley landraces. In general, grazing encouraged tiller production but reduced head number per unit area because of a higher tiller mortality or infertility. Seed number per head and seed weight were not affected by grazing except in one season. Grazing delayed heading and maturity and reduced plant height. Simulated and actual grazing produced similar effects on the different characters investigated.

This is the first of several papers that will present ideas on statistical method in agricultural research, especially in relation to the planning and analysis of experiments, based upon experience but not found explicitly discussed in standard textbooks. Indeed, some of the contents of these papers may appear to conflict with what can be found in books: closer examination is likely to disclose lack of real disagreement with the better texts. The first paper outlines a plan for the series. Thereafter, it concentrates on relations between agricultural scientists and statisticians and on some of the issues that are too easily overlooked when one of the former, often for good reason, chooses to be his own statistician.

Direct belowground nitrogen (N) transfer has often been reported where plants with contrasting nutrients acquisition strategies (N2-fixing and non-fixing) co-occur, and there is still a gap in the knowledge of the extent of this transfer in the top soil under the field conditions. However, assessment under field conditions is challenging. We hypothesized a practical application of the analysis of natural abundance of δ15N supplemented with an isotopic mixing model ‘IsoSource’ to understand the relative direct contribution of N2-fixing Alnus acuminata to wheat intercrop (non-fixing) N isotopic signatures. A field experiment was conducted in an andic soil of high lands in northern Rwanda to quantitatively determine the proportional contribution of nitrogen by Alnus acuminata to wheat vegetative tissue isotope signatures at different distances from the trees (1 m, 3 m, 5 m, and 7 m). The study involved the measurements and analyses of natural abundance of stable isotopes δ15N and isotopic mixing modeling by IsoSource. Leaf samples were collected from twigs of 10 years old Alnus acuminata grown on the terrace-risers, along with soil samples (0–20 cm) and wheat flag leaf samples across terrace at 1 m, 3 m, 5 m, and 7 m from trees for isotopic measurement. The chlorophyll content index of wheat flag leaf at the four points across terrace was estimated by means of SPAD meter 502. The δ15N proportional contribution by Alnus acuminata to wheat was obtained through IsoSource analysis. We noted a significant (p < 0·01) gradient in depletion of wheat δ15N signatures moving further away from the tree line of Alnus acuminata. The wheat at 1 m from the trees exhibited the δ15N values closer to that of the tree, while at 7 m, the crop δ15N signature was significantly different from that of the tree. An isotopic mixing model ‘IsoSource’ indicated that the tree N may have provided 33·6 ± 4·3 % of the wheat intercrop N at 1 m distance from the trees. Therefore, this study shows that the understanding of field-based crop N and nutrient transfer in agroforestry may be enhanced by analysis of the physiological basis of stable isotopes signatures.

Gac is a dioecious tropical and perennial climber. The fruit is a rich source of carotenoids and is used in traditional cuisine and medicine. Improving propagation methods using simple techniques would increase production and improve conservation in regional areas. This study evaluated temperature requirements for seed germination, the use of rooting hormones to strike female cuttings and the grafting of female scions onto seedling rootstock. Seed germination was optimised between 25 and 35 °C, with a maximum germination percentage of 91% at 30 °C. However, increasing storage time from 6 to 18 months under laboratory conditions (21 ± 1°C and 60% relative humidity) reduced germination and this was associated with seed weight loss, highlighting the need to develop storage guidelines, particularly for the higher temperature and humidity conditions where Gac is grown. Survival of softwood cuttings was improved from 53 to 77% with indole-3-butyric acid (IBA) (3–5 g/L) and semi-hardwood cuttings did not require IBA treatment. Both splice and wedge grafting techniques achieved a survival rate > 53% and with the youngest rootstock (4 and 8 weeks) this increased to > 85%. Further work could investigate the production potential of crops using cuttings and grafted plants.

The genotypic and phenotypic correlations and path-coefficients were studied in two different environments, using twenty fodder genotypes of cowpeas. Among quantitative characters, leaves/plant, branches/plant and stem girth were highly correlated with both green and dry matter yield, whereas among quality characters, total protein (per cent) showed significant association with digestibility (per cent). Based on path-coefficient analysis, leaves/plant and protein (per cent) were found to be the most important component characters. These two characters were also highly correlated at both the genotypic and phenotypic level and, therefore, selection based on leaves/plant is likely to be useful for simultaneous improvements in yield and quality of fodder in cowpeas.

Meloidogyne paranaensis is responsible for considerable losses in coffee production. Because of the distribution of this species in the main Coffea arabica producing regions, there is a need for management practices to ensure the sustainability of coffee production. In this work, we evaluated the agronomic performance of resistant clones of the Conilon coffee cultivar Vitoria Incaper 8142 in areas infested by M. paranaensis in the west region of Minas Gerais, Brazil. Clones 2V, 3V, and 6V presented the lowest number of nematodes per gram of roots and were considered resistant to M. paranaensis. All other clones were considered tolerant to this nematode, and one had good vegetative growth but allowed nematode reproduction. Clones of Vitoria Incaper 8142 of C. canephora represent an alternative to coffee production in areas infested by M. paranaensis including areas traditionally cultivated with C. arabica.

This article was published with an incorrect Title. The correct title should read:

‘SEED-ORIENTED PLANTING IMPROVES LIGHT INTERCEPTION, RADIATION USE EFFICIENCY AND GRAIN YIELD OF MAIZE (Zea mays L.)’

The original article has been rectified with the correct title and a footnote detailing the error has been inserted in the online PDF and HTML copies.

In Brazil, high-yield soybean [Glycine Max (L). Merrill] – corn (Zea mays L.) double cropping system might be nitrogen (N)-limited and additional N fertilization can be beneficial. Early application of N in soybean reduces the symbiotic N fixation (SNF) efficiency and/or establishment. One alternative to avoid SNF impairment is to apply N between the beginning pod (R3) and seed-fill (R5) stages through the use of controlled release fertilizers. In this study, N was applied at 50 kg ha−1 as common urea (CU) or controlled release urea (CRU) with different lag periods until N release starts (30 days, 60 days, or 1:1 mix of both lag times) in a randomized complete blocks design with six treatments and four replicates under tropical and subtropical conditions. CU was applied after soybean emergence (VE) or at the beginning pod (R3), and CRU only at VE. Using urea labeled with 15N isotope, we analyzed the N source used by soybean (fertilizer, soil, or SNF) and SNF parameters. On average, CRU – 30 days, CRU – 1:1 mix (30 + 60 days) and CU applied at the R3 stage increased grain yield by 9.2% (354 kg ha−1) compared to the control. N derived from all fertilizer treatment were almost 35 kg N ha−1, a high N recovery efficiency of 68%. The SNF was not impaired by CU and CRU and accounted for 71% (220 kg N ha−1) of total N uptake. In the conditions of the experiments, fertilization of 50 kg N ha−1 as CRU was shown to be effective to supply N in late soybean demand (R3 stage), increasing yield without damaging the SNF process in high-yield environments.