Continuous cropping of a tropical Ultisol with or without nitrogen fertilizer increased soil acidification and reduced soil organic matter and productivity. Addition of nitrogen fertilizer failed to increase yields. This was apparently due to the decline in soil pH, an increase in the amount of soluble aluminium, and consequent inefficient utilization of added nutrients. Continuous use of ammonium sulphate as a nitrogen source hastened the development of both surface and subsoil exchange acidity.

Trees are important sources of food in both the humid and semi-arid tropics. Some species have been exploited for centuries and are widely distributed around the world, others have been cultivated only in limited areas, while most are still essentially wild. The potential for rapid genetic improvement by clonal selection is enormous and well-proven by the recent history of some species. Trees can yield as much food per hectare as most C3 annual crops – although special problems may have to be overcome to ensure regular bearing of fruit and nut trees. Trees also offer great ecological and social benefits.

The numbers of bacteria and the nitrogen fixing efficiency of isolates of Rhizobium leguminosarum, R. ciceri and R. meliloti with appropriate legume crop species were determined from soils collected from a wide range of locations in Turkey with elevations between 500 and 2200 m. For vetch and lentil nodulated by R. leguminosarum, many native rhizobia are present in most locations but they often have limited nitrogen fixation capacity. However, for chickpea nodulated by R. ciceri, relatively small numbers of bacteria and the almost universal ineffectiveness of fixation capacity point to a need for artificial seed inoculation of chickpea crops as a future agronomic priority. The wide range of bacterial numbers, considerable geographic inconsistency and generally low effectiveness of the indigenous rhizobia associated with the annual Medicago spp. suggest that inoculation would initially be a sensible precaution for all sowings.

Biodiversidad del rhizobium en Asia occidental

Forage production of common vetch in semi-arid Mediterranean regions can be increased by varietal improvement. Dry matter content and crude protein yield were affected by environment more than crude protein content and harvesting date. Forage produced in environments where plants grew quicker was of lower dry matter content, higher crude protein content but of similar weight as forage produced in late environments. Variations in annual rainfall explained 35 to 76% of the total variation in dry matter yield.

Seed yam production potential of three yam species (Dioscorea rotundata, Dioscorea alata and Dioscorea cayenensis) was assessed for two systems – the traditional method using 100 to 200 g setts, and the mini-sett technique using 25, 20, 15 and 10 g setts cut from mother tubers. The mini-sett technique required only 6–33% of the number of tubers needed for the traditional planting system, and resulted in plants superior to those produced by the traditional method in all their production attributes especially in the case of D. alata and D. rotundata.

A four-year study from 1958 to 1962 showed that time of application of fertilizer nitrogen greatly influenced the yield of grain, the percentage of nitrogen and the crude protein of the grain under Nigerian conditions characteristic of the early maize cropping season from March to July. Split applications of nitrogen fertilizer significantly increased maize grain yield by 35 per cent when two equal doses were given one month and two months after planting; and by 31 per cent when four equal doses were supplied at planting and one month, two months and three months after seeding. Yield was significantly reduced when application was delayed two months after planting. High yields of maize were not obtained by supplying the whole of nitrogen fertilizer at one time, eidier at sowing or any time later during the growing season. However, applying all of the nitrogen fertilizer one month after planting significantly increased the percentage of nitrogen and of the crude protein content of the grain. The maize ear weight was favourably influenced by spreading the nitrogen application over the three-month period of the maize growth.

The effects of rootstock on tree development, leaf nutrient levels and yields of two old-clone lemon cultivars, Eureka and Villafranca, were studied. The largest canopy development and yields were obtained on Alemow and Volkameriana; red rough lemon failed due to foot rot; Rangpur lime trees were severely stunted; and Citremon induced high chloride and relatively low boron contents in the leaves.

Low genetic diversity acts as a major bottleneck in garden pea breeding, and diverse parents are required to generate new genetic material. The diversity of parents utilized in hybridization programme was ascertained following simple sequence repeats (SSR) markers. Thirty-six homozygous F7 progenies were isolated from three intervarietal crosses through shuttle breeding programme over a period of 6 years (2009–2014). Two experiments were conducted for two consecutive years 2014/15 and 2015/16, for evaluating the agronomic performance of progenies along with four commercial control cultivars. Analysis of variance (ANOVA) revealed that genotype, growing year and their interaction had significant effects on most of the traits. Line ‘DPP-SP-6’ recorded significantly higher pod yield/plant in comparison to all other genotypes in 2014/15, 2015/16 and for pooled over years. In addition, ‘DPP-SP-22’, ‘DPP-SP-7’ and ‘DPP-SP-17’ also performed statistically at par with best-performing check ‘Pb-89’ during both the years. These superior lines, in general, showed better pod filling, green pod colour, high shelling, sweetness and resistance to powdery mildew disease. These superior progenies could act as an alternative to the popular check varieties after their exhaustive evaluation over environments.

The effect of drought and temperature on the growth and development of bambara groundnut (Vigna subterranea (L.) Verdc.) was studied in controlled environment glasshouses in the United Kingdom. There were two landraces, S19-3 (from a hot, dry environment; Namibia) and Uniswa Red (from a cool, wet environment; Swaziland), two temperature regimes (23 °C and 33 °C) and three watering regimes (2006; fully irrigated), 2007 (drought imposed at 77 days after sowing (DAS)) and 2008 (drought imposed at 30 DAS)). Bambara groundnut responded to drought by slowing the rate of leaf area expansion and reducing final canopy size and total dry matter (TDM). Drought also caused significant reductions in pod dry matter, pod numbers and harvest index (HI), leading to a decrease in final yield that was different between landraces. Throughout the three growing seasons, landraces grown at 33 °C produced more TDM than the landraces grown at 23 °C. The two landraces differed in their phenology; S19-3 exhibited a reduced phenology where leaf numbers started to decrease before Uniswa Red at both temperatures, while Uniswa Red maintained the longest life cycle. The lowest pod yield was produced by Uniswa Red in 2008 at 33 °C (maximum of 35.5 gm−2), while S19-3 produced a minimum pod yield of 56.6 gm−2 at 33 °C, also in 2008. However, both landraces produced considerably more pod yield at 23 °C throughout the three growing seasons (minimum of 151 gm−2 and 162 gm−2 for Uniswa Red and S19-3, respectively). Under moderate drought, S19-3 at 33 °C gave the highest pod yield (365 gm−2) among the treatments throughout the three growing seasons and maintained HI better under drought. Despite being from a hot, dry environment, S19-3 also performed well at low temperature, which indicates the adaptation of S19-3 to low temperature that it also experiences in the country of origin.

Application of biochar to rice has shown to elicit positive environmental and agricultural impacts due to its physicochemical properties. However, the relationship between greenhouse gas (GHG) emissions, rice yield, and soil nutrient status under biochar amendment remains unclear. In this study, rice yield and methane (CH4) and nitrous oxide (N2O) emissions were quantified in response to biochar application rate (0, 10, 20, and 40 t ha−1) to early and late subtropical rice cropping systems. We found that application of 10 t of biochar ha−1 to early rice reduced average CH4 emission fluxes, while all biochar application rates diminished average emissions in late rice paddy. Total global warming potential (GWP) and GHG intensity (GHGI) were inherently greater in late rice than early rice cropping. In early rice, GWP and GHGI were found to be similar between soil control, 10 and 20 t of biochar ha−1 treatments, although the largest occurred in the 40 t of biochar ha−1 treatment, whereas in late rice cropping, they were not affected by biochar application rates. Compared to the nil-biochar application, biochar application at varied rates did not affect rice yield. However, compared to 10 t biochar ha−1, increasing biochar application rate to 40 t ha−1 significantly decreased total rice yield (sum of early and late cropping). Generally, application of biochar increased soil salinity and total Fe and Fe2+ content while reducing soil bulk density. Temporal effects of biochar application were noted on CH4 emission flux, soil temperature, and soil Fe2+ and Fe3+ in early rice; and soil temperature, salinity, NH4+-N, NO3−-N, and soil Fe2+ and Fe3+ in late rice. This study confirms that the application of biochar at the lower rate of 10 t ha−1 is optimal for maintaining rice yield while reducing GHG emissions. Moreover, the study demonstrates the potential benefit of biochar in sustainable subtropical rice production.

Biomass burning has links with a number of global concerns including soil health, food security and climate change. In central Côte d'Ivoire (West Africa), we conducted a field study to compare nutrient losses, soil fertility and yam yield in slash-and-burn versus slash-and-mulch agriculture. Trials involved five sites established in the dominant Chromolaena odorata fallows of the region, each consisting of paired plots: slash and burnt biomass (SB) versus slashed and unburnt biomass, but left to serve as mulch (SM). Carbon and five elemental nutrients were assessed in the aboveground biomass prior to burning and in ash after fires; losses were assessed by subtraction. The greatest proportions of loss occurred with C (95%), N (95%) and K (74%), corresponding to losses into the atmosphere of 3532 ± 408, 200 ± 36, 132 ± 36 kg ha−1. Six weeks after the fire, soil properties were assessed: soil organic C, total N and Mg2+ were higher in SM than in SB sites. At final harvest, yam tuber yield was twice as large in SM as in SB (18 ± 4 vs. 9 ± 2 Mg ha−1) with soil C, total N and K+ as the main influential soil parameters. The key finding was that the elements lost in greatest proportion during burning were those mostly influencing yam yields. Because a clear negative relationship between biomass burning and yam production has been established the promotion of the more productive, alternate slash-and-mulch system compared to slash-and-burn system, is warranted. The findings of our research can be used in support of developing a sustainable yam production system in the region and in West Africa more generally.

Cassava, a crop widely adapted in the tropics, has the important attribute of withstanding adverse environmental conditions better than do many other staple crops. The performance of an individual genotype, however, is influenced by the environment in which it grows. In Malawi, the heterogeneity of agro-ecologies requires the cumbersome and costly assessment of new cassava genotypes at many sites. This study was conducted, therefore, to test the feasibility of selecting only a few locations for cassava evaluation that would be representative of all the agro-ecologies in which cassava is grown in Malawi. Enormous environmental effects, largely contributed by the interaction between season and location, were manifested. Genotype×environment interaction, due largely to a third level interaction (genotype×season×location), was highly significant for all the traits studied. A principal component analysis scatter plot showed no particular grouping of environments, but a pair-wise comparison showed that some of the locations had limited genotype×environment interaction, indicating that it would be sufficient to use one of these sites for evaluating these traits. The value of the residual was often large, probably as an effect of environmental heterogeneity in the test sites. The authors conclude that cassava genetic improvement will continue to be slow if Malawi is used as a single breeding zone. They recommend a much finer grouping of the locations and the use of smaller plot sizes to allow more clones to be tested at more sites for the same cost. Locations may be selected for intensive cassava breeding work from those that give the best discrimination between genotypes while having insignificant genotype×environment interactions in a relatively large number of environments.

Maize (Zea mays) seed orientation at planting can influence emerging leaf angle. If leaf angle were consistent among plants without leaf overlap, large numbers of these bilaterally symmetrical plants could be arranged to optimize light interception and possibly increase grain yields or maintain grain yield with a lower population. The objectives were to evaluate the effect of seed orientation in soil on the angle of maize leaves relative to the planted row and on emergence rate. Seeds were planted 2.5 cm deep in diverse combinations of flat, cotyledon down, cotyledon up, on their side, radicle up and radicle down. Each seed orientation was repeated 10 times. Data on days to emergence and leaf angle were collected. In three experiments, maize seeds planted flat with the cotyledon up resulted in homogenous and faster emergence, and maize leaves aligned perpendicular to the direction of the maize row. Similar results were achieved with maize seeds planted parallel to the row with the radicle down. Random placement of maize seeds resulted in random orientation of maize leaves and lower emergence rates. The effects of controlled leaf geometry could facilitate planting higher populations with the potential for increasing grain yield and/or allow the maintenance of grain yields while reducing seed rates.

Seedlings of 48 genotypes of barley were grown in a glasshouse in different rooting media to determine the possible range of variation in root and shoot systems. Plants grown in nutrient solution produced shoots which were larger than those grown in sand and perlite, but in sand and perlite almost twice as much root length was produced per unit of shoot area. There were large differences between genotypes in both root and shoot growth.

The effects of growing medium on rooting were studied in more detail on six of the genotypes. Plants grown in soil and nutrient solution had longer lateral roots than those grown in sand and perlite. Genotypic variation in growth was large but the range of root and shoot growth in a particular medium was similar. Generally, the ranking of the genotypes was similar in both studies and in all media.

The present study is to characterise the non-structural carbohydrate (NSC) status and its catabolism along with elongation growth in rice cultivars either possessing or not possessing the Sub 1 quantitative trait locus (QTL), i.e. Swarna and Swarna Sub1 exposed to seven days of complete submergence. During submergence, Swarna accelerated the rate of stem and leaf elongation and rapidly consumed NSC. In contrast, Swarna Sub1 consumed energy resources more slowly and maintained similar growth rate to that of non-submerged plants. Swarna Sub1 showed better utilisation of carbohydrate than that of Swarna by progressive induction of alcohol dehydrogenase, starch phosphorylase and total and α-amylase enzyme activity during submergence. Overall, submergence tolerance conferred by the Swarna Sub1 QTL is correlated with better maintenance and utilisation of NSC than that of Swarna.

The effects of sole and intercropping of rainfed maize (Zea mays L.) were evaluated with soybean (Glycine max L.) and groundnut (Arachis hypogea L.) on crop yield, weed smothering efficiency (WSE) and nutrient (NPK) balance at Eastern Himalayan Region (EHR), India. Grain yield of maize was highest (3886 to 4110 kg ha−1) in the solitary system followed by maize-soybean intercrops at 1:2 rows. However, system productivity as well as production efficiency was higher by 47.3-63.3% and 39.5-58.4%, respectively in intercropping with groundnut at 1:5 rows compared to solitary maize. WSE was relatively higher to solitary soybean and was comparable to maize-groundnut intercropping at 1:5 row proportions. Similarly, NPK uptake was higher in intercropping of maize-soybean systems at 1:5 row proportions. Inclusion of legumes as intercrops in predominantly solitary rainfed maize may improve the system productivity while sustaining the nutrient availability in the vast uplands of the EHR and other similar rainfed hilly ecosystems.

A technique for observing the effects of soil physical and other factors on root growth was evaluated, using glass tubes packed with soil. The number of root intersections observed on a grid at the interface between the soil and glass was correlated with the number of root ends counted within the soil core. Comparatively small differences in the dry bulk density of a structureless sandy loam (1.25 and 1.50 g cm−3) had much larger effects than differential watering treatments on the pattern of root growth of lettuces (Lactuca sativa). Loosening the soil to depth (with additional fertilizer) increased the availability of water, under both wet and dry conditions, and improved water use efficiency, primarily through effects on root activity.

Objectives of different intercrop experiments need to be kept in view while analysing the data from them. There is no single straightforward way of analysing the data and certain situations require innovative approaches. Types of situations that are encountered in dryland agricultural research are exemplified and methods of meaningful analysis and interpretation of data from them are indicated here. Agronomically-sound meanings are imputed for different ways of calculating LER. Use of the concept ‘Staple Land Equivalent Ratio’ for assessing intercrop systems in particular situations is illustrated.

A field experiment was conducted in 2002/03 (year 1) and repeated in 2003/04 (year 2) to study the competitive ability of 10 winter barley (Hordeum vulgare) cultivars against common poppy (Papaver rhoeas) and ivy-leaved speedwell (Veronica hederifolia). The phytotoxic (or allelopathic) activity of barley extracts was also determined in the laboratory using a perlite-based bioassay with barnyard grass (Echinochloa crus-galli). In the field, biomass of both weeds was reduced more (65–79%) by the competition of Alpha, Esterel, Terova or Lignee 640 barley cultivars, than with Aspen or Tersey. Biomass of ivy-leaved speedwell in competition with each barley cultivar was significantly lower than that of common poppy. In year 1, the six-row barley cultivars caused greater weed biomass reduction than the two-row, but this was not the case in year 2. Grain yield of Tersey, Aspen and Goldmarker cultivars in herbicide treatments was greater by 41, 33 and 17%, respectively, than from the corresponding herbicide untreated plots. However, grain yield of Terova, Alpha, Esterel and Lignee 640 was not significantly affected by the presence of weeds. In the laboratory, barley extracts affected the total fresh weight or root length of barnyard grass more than its germination. The germination, root length or total fresh weight inhibition on barnyard grass caused by the two six-row barley extracts was greater (43, 48 and 56%, respectively) than that caused by the eight two-row extracts (22, 34 and 43%, respectively). The results of this study indicated that barley cultivars with great competitive and/or phytotoxic ability could be used in sustainable cereal production systems in order to minimize herbicide usage.

Bambara groundnut (Vigna subterranea) is a grain legume crop, which is increasingly popular as food in rural areas across the African continent. However, reliable information pertaining to management of the crop is limited. Field experiments were conducted in Swaziland in the 1998/99 and 1999/2000 cropping seasons to determine the influence of sowing date and environmental factors on the growth, development and yield of bambara groundnut. In the 1998/99 season, seeds of one local landrace were sown on six dates between mid-September 1998 and mid-February 1999. In 1999/2000, seeds of two local landraces were sown on six dates between mid-October 1999 and late January 2000. The highest pod yield and total dry matter production were achieved in November sowings, with maximum pod yields of 1.3 and 0.64 t ha−1 for the 1998/99 and 1999/2000 seasons, respectively. Earlier sowing and successive delays in sowing from November caused substantial yield declines of as much as 72–75%. Sowing date influenced yields of bambara groundnut through the effect of temperature and daylength on plant development. For the landraces used in the study, while the rate of progress from sowing to flowering was influenced by temperature, the rate of progress from flowering to podding was influenced largely by daylength. The practical implications of the results for increased bambara groundnut production are discussed.