Diversification economies and specialisation efficiencies in a mixed food and coffee smallholder farming system in Papua New Guinea

Smallholder farming systems in Papua New Guinea are characterised by an integrated set of cash cropping and subsistence food cropping activities. In the Highlands provinces, the subsistence food crop sub-system is dominated by sweet potato production. Coffee dominates the cash cropping sub-system, but a limited number of food crops are also grown for cash sale. The dynamics between sub-systems can influence the scope for complementarity between, and technical efficiency of, their operations, especially in light of the seasonality of demand for household labour and management inputs within the farming system. A crucial element of these dynamic processes is diversification into commercial agricultural production, which can influence factor productivity and the efficiency of crop production where smallholders maintain a strong production base in subsistence foods. In this study we use survey data from households engaged in coffee and food crop production in the Benabena district of Eastern Highlands Province to derive technical efficiency indices for each household over two years. A stochastic input distance function approach is used to establish whether diversification economies exist and whether specialisation in coffee, subsistence food or cash food production significantly influences technical efficiency on the sampled smallholdings. Diversification economics are weakly evident between subsistence food production and both coffee and cash food production, but diseconomies of diversification are discerned between coffee and cash food production. A number of factors are tested for their effects on technical efficiency. Significant technical efficiency gains are made from diversification among broad cropping enterprises.

Timing, magnitude, and location of initial soluble aluminum injuries to mungbean roots

Despite a century's knowledge that soluble aluminum (Al) is associated with acid soils and poor plant growth, it is still uncertain how Al exerts its deleterious effects. Hypotheses include reactions of Al with components of the cell wall, plasmalemma, or cytoplasm of cells close to the root tip, thereby reducing cell expansion and root growth. Digital microscopy was used to determine the initial injuries of soluble Al to mungbean (Vigna radiata L.) roots. Roots of young seedlings were marked with activated carbon particles and grown in 1 mm CaCl2 solution at pH 6 for ca. 100 min (control period), and AlCl3 solution was added to ensure a final concentration of 50 muM Al (pH 4). Further studies were conducted on the effects of pH 4 with and without 50 muM Al. Four distinct, but possibly related, initial detrimental effects of soluble Al were noted. First, there was a 56-75% reduction in the root elongation rate, first evident 18-52 min after the addition of Al, root elongation continuing at a decreased rate for ca. 20 It. Decreasing solution pH from 6 to 4 increased the root elongation rate 4-fold after 5 min, which decreased to close to the original rate after 130 min. The addition of Al during the period of rapid growth at pH 4 reduced the root elongation rate by 71% 14 min after the addition of Al. The activated carbon marks on the roots showed that, during the control period, the zone of maximum root growth occurred at 2,200-5,100 mum from the root tip (i.e. the cell elongation zone). It was there that Al first exerted its detrimental effect and low pH increased root elongation. Second, soluble Al prevented the progress of cells from the transition to the elongation phase, resulting in a considerable reduction of root growth over the longer term. The third type of soluble Al injury occurred after exposure for ca. 4 h to 50 mum Al when a kink developed at 2,370 mum from the root tip. Fourth, ruptures of the root epidermal and cortical cells at 1,900-2,300 mum from the tip occurred greater than or equal to4.3 h after exposure to soluble Al. The timing and location of Al injuries support the contention that Al initially reduces cell elongation, thus decreasing root growth and causing damage to epidermal and cortical cells.

Seasonal patterns of growth, dehydrins and water-soluble carbohydrates in genotypes of Dactylis glomerata varying in summer dormancy

Background and Aims Summer dormancy in perennial grasses has been studied inadequately, despite its potential to enhance plant survival and persistence in Mediterranean areas. The aim of the present work was to characterize summer dormancy and dehydration tolerance in two cultivars of Dactylis glomerata (dormant 'Kasbah', non-dormant 'Oasis') and their hybrid using physiological indicators associated with these traits. Methods Dehydration tolerance was assessed in a glasshouse experiment, while seasonal metabolic changes which produce putative protectants for drought, such as carbohydrates and dehydrins that might be associated with summer dormancy, were analysed in the field. Key Results The genotypes differed in their ability to survive increasing soil water deficit: lethal soil water potential (ψ(s)) was -3(.)4 MPa for 'Kasbah' (although non-dormant), -1(.)3 MPa for 'Oasis', and -1(.)6 MPa for their hybrid. In contrast, lethal water content of apices was similar for all genotypes (approx. 0(.)45 g H2O g d. wt(-1)), and hence the greater survival of 'Kasbah' can be ascribed to better drought avoidance rather than dehydration tolerance. In autumn-sown plants, 'Kasbah' had greatest dormancy, the hybrid was intermediate and 'Oasis' had none. The more dormant the genotype, the lower the metabolic activity during summer, and the earlier the activity declined in spring. Decreased monosaccharide content was an early indicator of dormancy induction. Accumulation of dehydrins did not correlate with stress tolerance, but dehydrin content was a function of the water status of the tissues, irrespective of the soil moisture. A protein of approx. 55 kDa occurred in leaf bases of the most dormant cultivar even in winter. Conclusions Drought avoidance and summer dormancy are correlated but can be independently expressed. These traits are heritable, allowing selection in breeding programmes.

Synthesis of soluble phosphate polymers by RAFT and their in vitro mineralization

Soluble linear (non-cross-linked) poly(monoacryloxyethyl phosphate) (PMAEP) and poly(2-(methacryloyloxy)ethyl phosphate) (PMOEP) were successfully synthesized through reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization and by keeping the molecular weight below 20 K. Above this molecular weight, insoluble (cross-linked) polymers were observed, postulated to be due to residual diene (cross-linkable) monomers formed during purification of the monomers, MOEP and MAEP. Block copolymers consisting of PMAEP or PMOEP and poly(2-(acetoacetoxy) ethyl methacrylate) (PAAEMA) were successfully prepared and were immobilized on aminated slides. Simulated body fluid studies revealed that calcium phosphate (CaP) minerals formed on both the soluble polymers and the cross-linked gels were very similar. Both the PMAEP polymers and the PMOEP gel showed a CaP layer most probably brushite or monetite based on the Ca/P ratios. A secondary CaP mineral growth with a typical hydroxyapatite (HAP) globular morphology was found on the PMOEP gel. The soluble PMOEP film formed carbonated HAP according to Fourier transform infrared (FTIR) spectroscopy. Block copolymers attached to aminated slides showed only patchy mineralization, possibly due to the ionic interaction of negatively charged phosphate groups and protonated amines.