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At the end of the second year of publication of Field Crops Research the Editor-in-Chief reviewd progress (Norman, 1980). Almost 14 years and more than 30 volumes later, when we have changed to a new format of the journal; when we have just about overcome the publication lag which arose from an increasing number of manuscripts accepted; when we are having to come to terms with new technologies developing around our interests; and when we have some concern that the geographical distribution of the journal and its sources of papers are not yet as wide as is in the best interests of an international journal and the research activity which it encourages, it is appropriate to undertake a review along similar lines to that of 1980. It is based on the publication of the last two years, 1991 and 1992, comprising Volumes 26-30 (inclusive). This excludes Volume 31 which was actually published in late 1992 but carries the 1993 date.

Response of cassava to row spacing and plant population density (0.62 plants m−2 in 180-cm rows; 1.23 plants m−2 in 90-, 180-, 270-, and 270- plus 90-cm (i.e. paired rows); and 2.46 plants m−2 in 90- and 180-cm rows), and to soybean intercrop at two row spacings of cassava (90 and 270 cm) was studied at a high latitude (27°S) in south-east Queensland, Australia, where low temperature limits a growing season to 9 months. Detailed observations were made in sole crops on leaf canopy structure and light penetration in the three row spacings at the medium density to allow an estimation of light availability for an intercrop between cassava rows. The low plant density or the 270-cm row plants produced the lowest total dry matter and tuber yield at harvest, while the two higher densities or the two narrower rows produced similar total and tuber dry weight. Intercropped cassava produced a similar tuber yield to the sole crop at the corresponding spatial arrangement, but total dry matter was lower in the former. Leaf area index was similar among the 90-, 180- and 270-cm row spacings in sole crops throughout the growth period. However, leaf area was unevenly distributed horizontally for a longer time as row spacing increased. This resulted in light penetrating the inter-row space for a longer period in wider rows in sole crops, more than 50% full sunlight reaching soil level for 90, 120 and 130 days after planting in the 90-, 180- and 270-cm rows, respectively. This light environment would be available for an intercrop if cassava growth is not affected by the intercrop. The results for cassava intercropped with soybean show that in fact cassava growth was reduced by the associated soybean, and hence light available for the soybean growth would have been more than that estimated above.

The development of yield in cassava, either as a sole crop or intercropped with quick-maturing soybean sown 1, 5 or 9 weeks after cassava planting, or a succession of two soybean sowings 1 and 14 weeks after planting, was followed at a high latitude (27°S) where the cassava growing season is limited to 9 months by winter temperatures. Competition, at least largely for nitrogen, restricted the growth of cassava, but after soybean harvest, leaf-area index increased such that there was little difference in interception of radiation among crops, and consequently growth rates and thus amounts of assimilate potentially available for tuber growth were similar. Competition from earlier-sown soybean greatly reduced branching by cassava. The reduced number of branches were sufficient to provide adequate leaf-area index, but were a reduced sink for assimilates during the main period of tuber growth. The slightly reduced assimilate supply available in early intercropped cassava was offset by the increased partitioning to tubers. As a result, soybean intercropping did not reduce tuber yield, except slightly in the case of double-intercropped cassava, but provided an additional yield of grain. Land equivalent ratio was particularly high at about 1.6 when soybean was sown within 5 weeks of cassava planting. When soybean was sown 9 weeks after cassava planting, land equivalent ratio was reduced to about 1.3 as a result of lower soybean yield.

The responses in the growth of peanuts (Arachis hypogaea L. cv. Florunner) to plant density and to spatial ratio (ratio of inter-row: intra-row spacing) in a tropical monsoonal environment were investigated. Biological yield (above-ground biomass plus pods) was unresponsive to spatial ratio over the range 1:1-1:7:19, but it increased markedly (12 600-16 900 kg ha−1), with increasing density up to the maximum density of 588 000 plants ha−1. In contrast, economic yield (commercially recoverable pods and kernels) was relatively unresponsive to plant density in the range of 88 000–394 000 plants ha−1, after which a marked decline was recorded (6 500 kg ha−1 pods or 4 900 kg ha−1 kernels, falling to 5 700 kg ha−1 pods or 4 300 kg ha−1 kernels). Economic yields were maximized at square plant-arrangements (6 900 kg ha−1 pods or 5 200 kg ha−1 kernels), but were relatively uneffected by increasing plant rectangularity from spatial ratios of 1:2.15-1:7.19 (6 100 kg ha−1 pods or 4 600 kg ha−1 kernels). The increase in biological yield with increasing plant was primarily attributed to differences in the amount of photosynthetically active radiation (PAR) intercepted (I), which was evident during both vegetative growth and kernel development. In contrast, I was unresponsive to spatial ratio. Neither density nor spatial ratio affected the average efficiency of conversion (Ec) of I to biological yield during vegetative growth (2.6-3.0 g MJ−1) nor during the entire life-cycle (2.1–2.3 g MJ−1). Average Ecm during kernel development was 55–60% of that during vegetative growth. Thus the higher economic yield of the square plant-arrangement was not associated with changes in I and Ec. Rather it was associated with greater partitioning of dry matter to reproductive yield and a greater proportion of total pods recovered at harvest.

Earlier experiments on cassava/soybean intercropping showed that early-maturing soybean reduced the growth of cassava, but that after soybean maturity partitioning of assimilates favoured tuber growth so that tuber yield was not reduced below that of sole cassava. An experiment was conducted to test the hypothesis that this favourable partitioning was due mainly to limited N availability to the intercropped cassava, and also to examine if performance of cassava/soybean intercropping was affected by the level of N application. There were three N treatments in both sole and intercropped cassava; no application, and application of 80 kg N ha-1 either at planting or at day 85 when soybean was harvested in intercropping. The experimental area was irrigated frequently to minimize the development of plant water stress. In sole-cropping, application of N at planting enhanced leaf area and dry-matter production during early stages of growth, but the effects did not persist until the final harvest. Dry-matter partitioning to tubers was reduced, and in consequence tuber yield tended to be less in this treatment than in the no-N control, although not significantly. Application at day 85 had negligible effects on dry-matter production and partitioning. The adverse effect of soybean on the growth and morphology of intercropped cassava was similar to, but more severe than, that of the no-N application in sole crop. Total dry-matter of intercropped cassava was always less than that of sole cassava in any N treatment. Lateral-branch production and leaf turnover were reduced by the presence of soybean, and the consequent reduction in shoot demand for assimilates resulted in an increased proportion of assimilates partitioned to tubers. When N was applied at planting, harvest index was higher in intercropped than in sole cassava, and tuber yield was similar in the two crops. Intercropping under no N application made only a slight further improvement in harvest index over the corresponding sole cassava, while severely reducing total dry-matter production. It appears, therefore, that the tuber-yield advantage of cassava/soybean intercropping is likely to be small under low availability of soil N.

Our previous work has shown that early-maturing soybean is suitable for intercropping with vassava at a high latitude (27°S) in south-east Queensland, Australia, as it does not effect the tuber yield. The present study examines whether later-maturing cultivars of soybean with higher yield potential might be more productive. Plant arrangement for cassava was the same in sole crop and in intercrop, while two soybean rows in every six rows were replaced by a row of cassava in intercropping. All soybean cultivars dominated intercropped cassava, and their dry-matter growth and seed yield were not affected by competition with cassava. Growth of cassava was, on the other hand, severely restricted by intercropped soybean, particularly by late-maturing types. After removal of early-maturing soybean, cassava recovered quickly to produce high leaf-area and effectively intercepted solar radiation. Consequential high total dry-matter production, combined with high assimilate allocation to tubers, resulted in tuber yield at the final harvest similar to that in sole cassava. After the removal of late-maturing soybean, however, recovery was poor, and with a short growing season remaining, tuber yields were only 50–60% of that of sole cassava. In addition to their adverse effect on cassave growth, late-maturing cultivars were not suitable as an intercrop because of low harvest indices and low light-conversion efficiency (dry matter produced per unit intercepted radiation), although total light interception during the whole growth of cassava/soybean intercrop was similar to that of sole cassava. The low overall light-conversion efficiency in intercropping with late-maturing cultivars was due to very low dry-matter production of soybean during pod-filling when light interception was still high.

Soybean ( Glycine max (L.) Merr.) has been shown to acclimate to, and produce high seed yield in, continuously saturated soil. In trials conducted to clarify the physiological mechanisms underlying this potentially valuable trait, soybean cv. Fitzroy was grown on beds in two years at Lawes, S.E. Queensland, and irrigated either continuously (saturated soil culture, SSC) or after 60 mm cumulative open-pan evaporation (conventional irrigation, CI). Shoot growth was initially lower in SSC but subsequently greater than that in CI, particularly during seed growth. Root and nodule growth, nitrogenase activity, and leaf conductance to water vapour were all greater in SSC. Seed yields were 24% and 52% higher in SSC in the two years, and these responses were associated with greater numbers of pods through reduced pod abortion, and higher individual seed weights, in SSC. Nitrogen assimilation by shoots in SSC during seed growth was approximately double that in CI, and during senescence the loss of leaf area and nodule function, and the withdrawal of nitrogen from the leaves, was delayed. It is suggested that enhanced leaf water-status in SSC resulted in greater photosynthesis and sustained nodule during pod growth, which in turn enabled continued nitrogen supply to the seeds and thus delayed the impairment of leaf function which follows nitrogen depletion.