A two-year study was undertaken in a tropical dryland agro-ecosystem to evaluate the effect of the application of soil amendments with contrasting chemical natures on crop productivity, grain yield, N-uptake and N-use efficiencies. The treatments involved the addition of equivalent amounts of N (80 kg N ha−1) through chemical fertilizer and three organic inputs at the beginning of the annual cycle: Sesbania aculeata shoots (high quality, C/N 16), wheat straw (low quality, C/N 82) and Sesbania+wheat straw (high and low quality combined, C/N 47), together with a control treatment. Test crops consisted of an annual sequence of rice and barley, sown in the rainy and winter seasons, respectively. Fertilizer and Sesbania inputs resulted in higher total net productivity (TNP) for the rice crop (47 % and 32 % increases over the control, respectively) than the combined (+28 %) and wheat straw treatments (+10 %). During the succeeding barley crop, maximum TNP was recorded in the Sesbania+wheat straw treatment (+52 %), followed by wheat straw (+43 %), fertilizer (+19 %) and Sesbania (+17 %). The TNP and grain yields of both crops added together were higher in Sesbania+wheat straw and fertilizer treatments compared to a single applications of either Sesbania or wheat straw. The Sesbania+wheat straw and fertilizer treatments resulted in more efficient utilization of N compared to the other treatments. Crop roots played a pivotal role in N-recovery from the soil and their N concentrations differed significantly (p < 0.05) due to the application of soil amendments. Across different treatments, crop root biomass was strongly correlated with crop N-uptake (r = 0.81, n = 10, p < 0.05), recovery efficiency (r = 0.81, n = 8, p < 0.05) and agronomic efficiency (r = 0.81, n = 8, p < 0.05). It is suggested that the combined application of high and low quality resources modulated N release, resulting in relatively higher productivity through the annual cropping cycle. Such combined inputs may prove useful in developing low input, environment friendly soil management practices in tropical dryland agro-ecosystems.

In cotton (Gossypium hirsutum), it is hard to determine the exact date when reproductive growth ceases on the basis of field observations, as compared to more visible factors such as the onset of flowering or boll opening. It is, however, essential to characterize the growth cycle in order to determine what varieties are suitable for planting in different climatic and local cropping conditions. We estimated the end of the effective flowering period on the basis of the opening date of the last flower giving rise to a first-position boll on fruiting branches (LFP1), and propose a simple method for estimating this date. This study, conducted in 2002 and 2003 at Okpara, Benin, involved a comparison of six cotton varieties planted at two different dates (June and July). Plants were monitored to determine the dates when flowers opened at each position on fruiting branches. The LFP1 indicator made a clear distinction between varieties. This highly heritable trait, which was found to be closely correlated with other earliness criteria, could be used to characterize the length of the growth cycle in cotton varieties.

Effective flowering time in Gossypium hirsutum cotton plants was studied with the aim of enhancing decision making on the best varieties to plant according to the planting date under rainfed cropping conditions. Trials were conducted at two sites in a cotton-growing area of Benin in 2002 and 2003. A split-split plot design with three replicates was used to compare 10 cotton varieties, with different growth cycle lengths and morphology, at three stand densities (42 000, 125 000, 167 000 plants ha−1) and two planting dates (standard planting in June and late planting). The flowering period was characterized by the mean first flower opening date (FF), which is an indicator of flowering earliness, and by the opening date of the last flower giving rise to a first-position boll on fruiting branches (LFP1). Effective flowering time (EFT) was calculated as the difference between LFP1 and FF. EFTs differed markedly in the 10 cotton varieties tested and this parameter could not be predicted on the basis of flowering earliness. Late planting and high planting rates delayed first-flower opening, accelerated last-boll development and reduced the effective flowering time. This latter factor should be taken into account in cotton breeding programmes so that varieties adapted to local rainfall constraints can be recommended to growers while also enhancing crop management sequences.

A breeding programme for resistance to Striga hermonthica in maize (Zea mays) was initiated in Côte d'Ivoire in 1994. Two extra-early populations, white (TZEE-W Pop STR) and yellow (TZEE-Y Pop STR), were formed from diallel crosses of the best adapted extra-early maturing maize germplasm in the West and Central African subregion. In an effort to improve the populations for Striga resistance, TZEE-W Pop was crossed to inbred 1368 STR (Tzi 3 STR), and TZEE-Y Pop to 9450 STR (Tzi 25 STR). The resulting F1 populations were carried through two backcross (BC) generations. S1 lines were developed from the BC2 and subjected to two cycles of random mating to generate TZEE-W Pop STR C0 and TZEE-Y Pop STR C0. These two populations were subjected to three cycles of S1 recurrent selection under artificial Striga infestation and several experimental varieties were extracted from the different cycles of the selection programme. The original populations (C0), improved populations, and experimental varieties were evaluated in two experiments under Striga-infested and Striga-free conditions. The primary objective was to determine the effectiveness of S1 recurrent selection in developing Striga-resistant extra-early maize varieties. Results of the performance tests showed that the populations were good sources of Striga-resistant varieties with high-yield potential under both Striga-infested and Striga-free conditions. The results have also confirmed the effectiveness of inbreeding, selection and hybridization, as well as the backcross breeding methods, as tools for the development of extra-early populations, synthetic varieties and inbred lines.

The feasibility of commencing tapping (‘opening’) of rubber trees for latex extraction at a lower stem girth (40 and 45 cm) than the currently recommended 50 cm was investigated in three different genotypes. The possibility of combining early opening with low frequency tapping and yield stimulation using Ethrel (LFT + E) was also examined. One of the genotypes tested, RRIC 121, gave a higher dry rubber yield, both per tapping and cumulatively over a given period, when opened at 40 cm than at 50 cm. Of the other two genotypes, one (RRISL 211) showed a clear reduction in yield with early opening, while the other (RRIC 102) did not show a significant yield response. Among the three genotypes tested, RRIC 121 showed the minimum depression in trunk girth increment. Analysis of yield components showed that the response of a given genotype to early opening and LFT + E is determined by the interaction between latex volume per tapping and dry rubber content (DRC), which were negatively correlated. RRIC 121 had a significantly greater DRC, which enabled it to maintain a higher dry rubber yield under early opening and LFT + E despite producing a lower latex volume than both the other genotypes. In contrast, despite producing a substantially greater latex volume than the other two genotypes, RRISL 211 did not produce a higher dry rubber yield because of its lower DRC. The higher DRC was also responsible for the greater response of RRIC 121 to yield stimulation with Ethrel, which reduced the plugging index and increased the initial latex flow rate. Early commencement of tapping in combination with LFT + E is therefore possible in rubber when amenable genotypes are selected, offering the potential of improving the economics of rubber production, especially for smallholders, in West Asia.

The main objective of this study was to quantify the genotypic variation of photosynthetic and gas exchange parameters of Hevea and to examine their relationships to dry rubber yield and its components. Canopy photosynthesis (Pc) of the genotype RRISL 211 was 20 % greater than that of RRIC 121. This was primarily due to RRISL 211's greater light-saturated leaf photosynthetic rates and a greater leaf area index in the top canopy stratum. Tapping significantly increased Pc in RRISL 211, but not in RRIC 121. The genotypic variation in photosynthetic capacity was not reflected in the overall dry rubber yield, which did not differ between the two genotypes. However, analysis of yield components showed that while RRISL 211 may have preferentially partitioned a greater proportion of its additional assimilates to increasing the latex volume and extending the root system, RRIC 121 partitioned more assimilates to increasing its dry rubber content through greater biosynthesis of rubber. The higher plugging index and the greater post-tapping girth increment of RRIC 121 were probably responsible for observed increases in its dark respiration following tapping. Although RRISL 211 had a greater transpiration efficiency, this did not provide a yield advantage as the trees were growing in an environment with adequate rainfall throughout the year.

Small-scale dairy farming has been suggested as a rural development option for Mexican campesino communities. However, there is a lack of information on how dairy farming systems operate. The objective of this paper is to analyse the social, productive and economic characteristics of small-scale dairy production systems in the central highlands in the northwest of the State of Mexico. These three characteristics were analysed on 69 farms using factor and cluster analysis. Five factors accounted for 68% of cumulative variance. Cluster analysis yielded three well-defined groups. A Kruskal–Wallis test was performed on the arable land area and the number of animals, and analysis of variance for milk yield. Economic analysis was undertaken using activity budgets. Results showed the relationships between scale and management methods and their effects on the income for the family. Families in only one of the three groups receive incomes from dairying that were above all Mexican poverty indices. This outcome is explained by the intensification in the management of their herds, which is reflected in higher milk yields, higher incomes and better access to government support schemes. Enhancement of milk production in the area studied needs differential policies which take in to account differences between the groups identified.