The role of water in the development and yield of the coffee crop (Coffea arabica L.) is reviewed. A period of water stress, induced either by dry soil or dry air, is needed to prepare flower buds for blossoming that is then stimulated by rain or irrigation. Although attempts have been made to quantify the intensity and duration of stress required, these have not yet been specified in ways that are commercially useful. Water must be freely available during the period of rapid fruit expansion to ensure large, high-quality seed yields. Depending on the time and uniformity of flowering this can occur at times when rainfall is unreliable, particularly in equatorial areas.

Although there are differences in their responses to drought, commercial cultivars have retained many of the characteristics adapted to the shady environment of the forests in the Ethiopian highlands in which C. arabica is believed to have originated. These include partial closure of the stomata when evaporation rates are high as a result of large leaf-to-air saturation deficits (>1.6 kPa), even if the soil is at field capacity. This is thought to be an adaptive mechanism that minimizes transpiration at high irradiances when the leaves are light-saturated.

Our understanding of the actual water use of coffee crops grown in diverse ways is imperfect. For mature crops, well supplied with water, the crop coefficient (Kc) appears to have a value in the range equivalent to 0.7–0.8 times the evaporation from a US Weather Bureau Class A pan. There is some evidence that Kc values are less than this on days when evaporation rates are high (>7 mm d−1). For immature crops allowance has to be made for the proportion of the ground area shaded by the leaf canopy, but this alone may underestimate rates of water use. Present methods of calculating crop water requirements for the purposes of irrigation scheme design and management are imprecise and, probably, subject to large errors depending on local circumstances.

The need for irrigation, and its role in controlling the timing of flowering, varies depending on the rainfall distribution, the severity of the dry season, and soil type and depth. Two geographic areas need to be distinguished in particular; those close to the equator with a bi-modal rainfall pattern and those at higher latitudes with a single rainy season and an extended dry season. Despite the international importance of irrigation in coffee crop production, the benefits to be derived from irrigation, in yield and in financial terms, have not been adequately quantified in either location. Allowable soil-water deficits have been specified for deep-rooting crops (2–3 m) on water retentive soils, usually linked to conventional over-tree sprinkler irrigation systems. Other, potentially more efficient, methods of irrigation are now available for coffee grower use, in particular, micro-jet- and drip-irrigation systems. However, there appears to be little advice, based on sound experimental work, on how to design and operate these to best advantage.

There is a need to interpret and apply the scientific understanding of the role that water plays in the growth and development of the coffee plant into practical advice that can assist the grower to plan and to use water efficiently, whether rainfall or irrigation, for the production of reliable, high-quality crops. Future research opportunities are identified.

A computer simulation model was developed to investigate strategies for control of the parasitic weed species of Orobanche. The model makes use of data from published literature and predicts infestation levels in a dynamic and deterministic way. It is predicted that sustainable control of the parasite can only be achieved by reducing the soil seed bank to levels of 1000–2000 seeds m−2 and maintaining it at that level in subsequent years. When cultural control methods such as hand weeding, trap/catch cropping, delayed planting, resistant cultivars and solarization were considered individually, a relatively high level of effectiveness was required to contain the soil seed bank. An integrated approach with a selection of appropriate cultural methods is therefore recommended for further testing and validation in the field. The simulations demonstrate the importance of preventing new seeds entering the soil seed bank and that although reducing the soil seed bank may not increase yield for the first few years, it will ultimately increase production.

Phosphorus at the recommended dose of 10 kg P2O5 ha−1 divided between three equal applications, one on each of 0, 7 and 14 d after Azolla inoculation (DAI), increased biomass production but sporulation was invariably inhibited. Of the different options tested, lowering the phosphorus application rate to 4–8 kg P2O5 ha−1 significantly improved sporulation in A. microphylla (strain 202) but there was a substantial reduction in biomass production. On the other hand, changing the schedule of phosphorus application from 0, 7 and 14 DAI to 0, 3 and 6 DAI did not hamper biomass production and improved sporulation frequency and sporocarp number in A. microphylla (strain 202), A. caroliniana and A. pinnata. It was comparable to the no-P treatment for the number of sporocarps, with slightly lower sporulation frequency. In these species, the sporulation frequency and sporocarp number of Azolla enriched with 30 or 60 kg P2O5 ha−1 and then grown without any further added phosphorus were higher than those of unenriched Azolla grown with 10 kg P2O5 ha−1 and mostly comparable to those of Azolla grown without phosphorus. Foliar spray of 2.5 μg ml−1 gibberellic acid (GA) solution (7 DAI) along with the application of 10 kg P2O5 ha−1 (split between 0, 7 and 14 DAI) to unenriched Azolla increased the sporulation frequency and number of sporocarps in A. microphylla (strains 202 and 203), A. caroliniana and A. pinnata, not only over that of phosphorus application alone but also over the untreated control. Combining the use of P-enriched Azolla (A. microphylla strains 202 and 203) with application of GA was more effective for increasing sporulation than was the use of P-enriched Azolla without GA, or application of phosphorus plus GA to unenriched Azolla.

Seedling growth in the nursery and the magnitude of shock experienced by the seedlings after transplanting can affect subsequent growth and development of transplanted rice (Oryza sativa). These two processes have not been adequately represented by rice growth simulation models. In this study, seedling growth in the nursery was described with respect to endosperm mobilization, dry matter (DM) distribution and seed size. In addition, the transplanting shock process was represented describing the crop development and growth in relation to seedling age at transplanting. These relationships, as two sub-models, were incorporated into CERES-Rice, a rice growth model, and their performances compared with independent field data. The nursery growth sub-model was also evaluated with another model, RIBHAB. Results of the comparison showed that the nursery growth sub-model, either with CERES-Rice or RIBHAB, closely predicted observed seedling growth. On the other hand, CERES-Rice overestimated root and leaf DM and underestimated culm DM, while RIBHAB underestimated all the growth traits considered in the evaluation. Transplanting shock period predicted by the sub-model closely mimicked observation, whereas CERES-Rice highly overestimated it. It is concluded that the developed nursery growth and transplanting shock sub-models can be incorporated into CERES-Rice and other rice growth models for better simulation of those growth processes.

Experiments to assess the yield and economic performance of a maize-groundnut rotation compared with continuous maize (both when inorganic fertilizer was applied to maize and when not), were conducted under management by smallholder farmers in Zimbabwe over six years. The experiment was planted on-station near Harare and at six smallholder sites in northeast Zimbabwe, predominantly on sandy soils. Fertilizer rates and practices were those used by farmers, as described in surveys. On-farm grain yields from continuous maize without fertilizer were generally in the range 0.5–0.8 t ha−1 over five years. Maize yield responses to inorganic fertilizer on smallholder farms were highly variable, but moderate (up to 29 kg grain per kg N) with adequate rainfall. With no inorganic fertilizer applied to maize, the on-station groundnut crop (producing 0.260–0.355 t ha−1 shelled grain) almost doubled the grain yield of the following maize crop (in 1995–96), increasing output from 2.46 t ha−1 to 4.61 t ha−1. Where inorganic fertilizer was applied to maize, the rotation produced even more additional maize grain (an increase of 2.93 t ha−1). Up to 0.50 t ha−1 extra grain was obtained in the second year of maize following groundnut (1996–97). With inorganic fertilizer, groundnut improved the grain yield of following maize crops at only two of five on-farm sites. Without fertilizer, the groundnut rotation increased maize grain yields at five on-farm sites by an average of only 0.28 t ha−1. For the on-station groundnut and two subsequent years with maize, discounted net benefits (DNBs) over cash costs (seed and fertilizer) were greater for the rotation than for continuous maize, irrespective of whether or not inorganic fertilizer was applied. When labour costs were added, continuous maize plus fertilizer showed better returns than did the rotation, while the returns for the rotation and continuous maize without fertilizer were almost the same. On-farm the rotation was far less profitable. At only two sites, DNBs over cash costs were higher for the rotation whereas DNBs over all costs (including labour valued at a local casual-worker wage) were always negative or close to zero. At three sites, it was far more profitable to grow continuous maize, especially with fertilizer. These findings of low groundnut yield, marginal to zero profitability, and high labour cost of groundnut-maize rotations, support and explain the general trend by smallholder farmers to reduce groundnut area in Zimbabwe.

On-farm experiments were conducted between 1990–91 and 1996–97 in the Indian districts of Jalandhar (Punjab) and Ghazipur (Uttar Pradesh), on rice-wheat cropping systems. The aim was to compare yields and net returns from three treatments: (i) farmers' nutrient management practices; (ii) integrated use of organic manures and fertilizer; and (iii) NPK fertilizer inputs alone. Productivity of the rice-wheat systems, in terms of grain yield per unit area, was greater in Jalandhar district than in Ghazipur district. In Jalandhar, a high productivity zone, greatest yields were achieved with integrated use of green manure and fertilizer NPK inputs, while in Ghazipur, a low productivity zone, yields were highest with inputs of fertilizer NPK alone. Increases in yield due to these improved practices, over farmers' practice, were 6.98% in Jalandhar and 46.6% in Ghazipur. At both locations, net returns were greater with the use of fertilizer NPK alone. However, benefits from NPK alone over farmers' practice were 6.96% in Jalandhar and 79.6% in Ghazipur. After 11 years of a long-term experiment, at Ludhiana (Punjab) and Faizabad (Uttar Pradesh) soil organic-C and available phosphorus contents have increased, and available potassium content decreased compared with the initial levels.

Instructions are given for the presentation of the results of statistical analyses in Experimental Agriculture. Statistical codes accepted by the journal are defined. Appropriate styles of presentation are illustrated for estimated parameters and variances for a selection of standard statistical analyses. The value of presentations of results of significance tests is discussed. Formats for acceptable tables and graphs are shown. References to further guiding texts are included for non-standard situations.