Plants of the photoperiod-sensitive, late-maturing pigeonpea (Cajanus cajan) cv. KAT777 were grown in pots in modified field environments at Katumani, Kenya. They were transferred at different durations after emergence from natural short days (SD, 12.6 h d−1) to artificially-extended long days (LD, 15.0 h d−1), and vice versa, under both ambient (19 °C) and warmer (26 °C) temperatures created beneath p olythene enclosures. All plants at 19 °C flowered within 106–160 d after emergence whereas only those transferred from LD to SD flowered at 26 °C during the investigation (202 d). A well-defined photoperiod-insens itive pre-inductive phase (a1) was detected after emergence; it lasted for 26 d at 19 °C but increased to 49 d at 26 °C. Thereafter, SD hastened and LD delayed progress to flowering until a third pha se, the photoperiod-insensitive post-inductive phase (a3) of pre-flowering development. At 19 °C, a3 was 66 d while the duration of the inductive phase in SD (IS) was 25  d and in LD (IL) it was 72 d. Plants were also moved from ambient to warmer temperatures and vice versa within either SD or LD at different durations after emergence. In SD all plants flowered during the investigation ( 250 d) whereas in LD only the plants transferred from the warmer to the ambient temperature regime flowered. During the initial stages of development plants were less sensitive to supra-optimal temperatures so that developmental progress from emerg ence to first flowering was the same whether plants were held at warmer or ambient temperatures during the first 35 d from emergence. Furthermore, plants transferred from the ambient to the warmer temperature in SD at any time from 49 to 77  d from emergence flowered at similar times to those kept at ambient temperature from emergence. Since a1 = 26 d and a1 + IS = 51 d, we sugg est that these results imply that exposure to supra-optimal temperature in SD during the latter 60% of the photoperiod-sensitive inductive phase (IS) of pre-flowering development delayed progress to flowering. In contrast, expos ing plants to supra-optimal temperature during either the photoperiod-insensitive pre-inductive phase (a1) or part of the photoperiod-insensitive post-inductive phase (a3) or during the first 40% of the photo period-sensitive inductive phase did not delay progress to flowering.

Most farming systems in semi-arid West Africa rely on organic matter recycling for maintaining soil fertility. The cycling of biomass through ruminant livestock into dung (faeces) and urine that fertilize the soil has long been an important factor in t he nutrient cycling processes of these integrated, mixed crop/livestock systems. While dung greatly improves soil properties and crop yields, little is known about the effects of urine on soil chemical properties and the impact of dung and urine on crop p roduction. An average voiding of sheep urine applied to a sandy, siliceous soil in the Republic of Niger increased soil pH, available phosphorus and ammonium levels dramatically in the upper 10–15 cm of soil, especially during the first week following application. Losses of applied urine nitrogen via volatilization were in the order of 30–50%. A four-year field trial was conducted on the same soil type to evaluate the effects on pearl millet and weed yields of corralling cattle o r sheep overnight on cropland (dung plus urine application) for one, two or three nights, every one, two or three years versus the effects of applying only dung at the same application rates and intervals achieved with corralling. The main results of this field trial were that (1) urine had large positive effects on millet grain, threshed panicle, leaf, stem and weed yields, (2) sheep dung was more effective than cattle dung in increasing yield, (3) two nights of dung application was adequate for maximum yield and (4) the positive effects of dung and urine on yield lasted two to three cropping seasons after application.

An experiment to determine weed spectrum, weed seedling numbers, temperature and nutrient changes in manure heaped for one to five months was undertaken over two seasons. Weed seedling numbers in manure heaped for one to five months decreased significa ntly by 65–70%. The weed spectrum comprised 17 broadleaf weed species of which Amaranthus hybridus, Leucasmartinicensis and Nicandra physalodes were most prevalent. There were six grasses with Eleusine indica and Cynodon dactylon being dominant. Temperature increased from 20 °C in the unheaped manure to averages of 34 and 42 °C in manure heaped for three and five months respectively in the two seasons. In both season s nitrogen and potassium became more available as the period of manure heaping increased while phosphorus decreased. It was concluded that heaping manure for three months significantly reduces weed seed viability and enhances the availability of some nutr ients.

An experiment with the objective of evaluating the performance of 15 clones of rubber (Hevea brasiliensis) was conducted in the Konkan region of Western India. The clones under evaluation were RRII 5, RRII 6, RRII 105, RRII 208, RRII 308, RRIC 52, RRIC 100, RRIC 102, RRIC 105, RRIM 605, PB 260, PB 310, PB 311, PR 255, and PR 261. The region is a trial environment for the crop and experiences more than seven rainless months and severe drought in the summer months. Data on monthly girth growth w ere collected for six years from a trial with randomized block design. The growth of clones in terms of monthly girth increment growth (GIN, cm month−1) seasonal mean girth increments (MGIN, cm season−1) and mean relative increment rates (MRIR, mm cm−1 season−1) as well as annual MGIN (cm a−1) and MRIR (mm cm−1 a−1) was studied. Correlation analysis was performed to understand the effect of seasonal growth on the final growth. At the beginning of the study, the largest girth noted was for the clone RRII 6 (22. 5 cm) followed by RRII 208 (22.0 cm). PR 261 with a girth of only 14.2 cm was the least vigorous among the clones. A large portion of the growth occurred in the wet season only. During the dry season the growth rates of the clones declined substantially and decreases in girth ranging from 0.2 mm to 0.5 mm were noticed in most of the clones. At the end of the study period the largest girth observed was for clone RRII 208 (49.3 cm) and the lowest for PR 261 (39.3 cm). The highest proportion of tappable trees noted was for clone RRII 208 (52.4%) and the lowest for PR 261 (2.7%). The pooled average of tappable trees was on ly 17.5%. The data revealed that the immaturity period for Hevea in the region will not be less than 9 years under rainfed conditions. From the analysis based on the final girth it was concluded that clones RRII 208, RRIC 52, RRII 6, RRIC 100 and RRIC 102 are more tolerant to drought while RRII 105, RRIC 105, RRII 5, RRIM 605, PB 310, PB 260, PB 311, PR 255, RRII 308 and PR 261 are less tolerant. The results of correlation indicated that by analysing the growth, potentially drought-toleran t clones can be identified.

Plants of yam, taro, tannia, cassava and sweet potato were raised under shade or in full sunlight and the effect of shade on leaf chlorophyll and carotenoids was examined to determine and compare the relative shade tolerance and adaptability of the var ious species. All five species of root crops adapted to shade. The chlorophyll concentration was higher, while the chlorophyll a:b ratio, carotenoids per unit chlorophyll and the weight per unit area of leaf were lower in the shade than in the su n in yam, tannia, taro, cassava and sweet potato. All species had larger leaves and more chlorophyll per leaf in the shade. The extent of the changes, however, differed between species. The aroids (taro and tannia) appeared to be shade-tolerant species as their chlorophyll a:b ratios changed less than those of the other species in the shade, suggesting that their light-harvesting systems may be normally adapted to shade conditions. Taro and tannia also adapted to shade by a greater proportional i ncrease in leaf size, a smaller reduction in leaf weight per unit area and a greater proportional increase in chlorophyll and carotenoids per leaf than the other species. Yam compensated for shade by having a large proportional increase in leaf size and a ppeared to be moderately tolerant of shade. Sweet potato and cassava appeared to be the least tolerant of shade of the major tropical root crops.

Leucaena (Leucaena leucocephala) is most preferred by development workers for agroforestry in the mid-altitude (600–1600 m) agro-ecological zone of North-West Cameroon because its seeds are common and inexpensive. This study was prompted by farmers' reluctance to accept leucaena for agroforestry because its early growth is poor on acid infertile soils prevalent in the area. Leucaena was planted using four-month-old potted plants and, from four months after planting, the shrub was cut five times in 20 months at 120 day intervals. Manuring improved leucaena's growth and biomass at sites with acid and non-acid soil alike. Total biomass responded linearly (R2=0.97) to manure rates at the acid and infertile site and curvilinearly (R2=0.95) at the non-acid site. Total leafy biomass from the first cut and subsequent prunings was highest at 12 months after planting. Manuring increased rooting depth and this contributed to the plant's observed ability to cope with moisture stress during the dry season. The economics of manure use for tree establishment on acid infertile soils for agroforestry systems needs further study.

Previously published data from two tea experiments in Tanzania and Malawi were re-analysed to identify factors responsible for the marked seasonal peaks and troughs of production observed at the two locations. Simulation modelling indicated that the influence of seasonal variations in temperature or photoperiod on shoot growth rates alone were not able to explain the occurrence of a large peak in September/October followed by smaller and progressively wider peaks in December, February and April in well-irrigated, well-fertilized tea at the two sites. Various mechanisms to explain these seasonal variations in yield are discussed, but it is concluded that the best explanation is the regulation of the numbers of shoots available for harvesting through the effect of photoperiod on shoot activity. The significant production peak normally obtained in September/October at both locations can then be explained by the release of a large number of buds from their resting state around the time of the winter solstice in June. Subsequent peaks are due to successive cohorts of shoots released from apical dominance when the preceding peak is harvested.