Suboptimal Yields Research Articles

Effects of adding moraine soil or shell sand into peat soil on physical properties and grass yield in western Norway

In terms of agricultural use, peat soils have weak structure, high water content, insufficient soil aeration and poor thermal properties resulting in suboptimal physical properties and yields of grass. During the period 1978–1995, a long-term field trial was conducted on highly decomposed peat soil in order to investigate the impact of adding mineral materials to improve soil characteristics and increase grass yield. Shell sand or moraine soil (200, 400 or 800 m3 ha−1) was incorporated into peat soil. Generally, addition of both shell sand and moraine soil improved the physical properties of the soil and grass production. During the first nine years, shell sand (400 m3 ha−1) was the most efficient. Thereafter, moraine soil (400 and 800 m3 ha−1) seemed most beneficial. This study indicates that additions of shell sand or moraine soil to peat are appropriate methods to improve and conserve the physical properties and cropping potential of these vulnerable soils.

Understanding Low Rates of Technology Adoption by Women Farmers: A Case Study of the Determinants of Adoption of Improved Sorghum Varieties by Women Farmers in Mbeere District, Kenya

The paper acknowledges the increasing recognition of women's contribution in agricultural and food production, both in terms of provision of labour and in the day-to-day management of farm households and farm activities. However, despite women's increased contribution in farming, not much is understood about their decisions on whether or not to adopt available agricultural technologies. Instead, majority of women farmers in Sub-Saharan Africa tend to be involved in subsistence farming with little use of improved technologies, which in turn translates into sub-optimal yields and low productivity. This paper identifies and analyses the factors that influence smallholder women farmers' decisions to adopt improved sorghum varieties in a marginal agricultural ecological zone in Kenya. A total of 81 farm households of whom 41 were female managed in Mbeere District were interviewed with the aid of a structured questionnaire. The data on various institutional, infrastructural, farm/farmer characteristics as well as technology attributes was analysed using a logit regression model. The analysis revealed that non-yield attributes of improved varieties do affect the probability of adoption. Such attributes in the case of sorghum include taste, ease or difficulty of processing the grain and proneness to attack by birds. Since women play a major role in agricultural and food production in much of Sub-Saharan Africa, the implications of these results are that more and more women should be encouraged to participate in later stages of technology development and evaluation. This would ensure that their views with regard to other important attributes besides yield were incorporated, which in turn would make improved technologies more appealing to farmers. Journal of Agriculture, Science and Technology Vol.3(1) 2001: 30-40

Effect of arbuscular mycorrhizal fungi and phosphorus fertilization on the post vitro growth and yield of micropropagated strawberry grown in a sandy loam soil

Strawberries (Fragaria ×ananassa Duch.) grown in alfisols of semiarid areas in India results in suboptimal yields. Low organic carbon and low phosphorus (P) availability, in addition to high P fixation, affects P availability drastically, even when it is applied externally. The benefit to the yield of micropropagated strawberry Fragaria ×ana nassa 'Pajaro' through inoculation with arbuscular mycorrhizal (AM) fungi and P application was examined in a field experiment. AM response was evaluated at four doses of P (50, 100, 150, and 200 kg P·ha–1) in a high P-fixing capacity and P-deficient alfisol. At harvest, all inoculated plants, except those at the highest level of applied P (200 kg·ha–1), had larger fruit yields per plant, unit mass, number of runners, higher shoot dry matter, and shoot P content. However, the AM response as measured by yield varied with P concentration. Inoculated plants had a significantly greater fruit yield when grown at 150 kg P·ha–1, and the yield was comparable with uninoculated plants grown at 200 kg P·ha–1. The external P requirements were 71 kg·ha–1 for mycorrhizal and 106 kg·ha–1 for nonmycorrhizal strawberry plants to obtain 90% of the maximum fruit yield. In terms of P fertilization, this corresponds to a savings of 35 kg·ha–1. The percent mycorrhizal root length colonization, both in inoculated and noninoculated plants, was not found to differ significantly with P application.Key words: strawberry, P fertilization, mycorrhizal dependency.

Comparison of nitrogen use efficiency of a newly developed sorghum hybrid and two improved cultivars in the Sahel of West Africa

In Sahelian areas such as Niger, West Africa, grain sorghum [Sorghum bicolor (L.) Moench] is grown under conditions of low soil nitrogen (N) availability on degraded land with little or no fertilizer N application. Nitrogen use efficiency (grain weight per unit of N supplied from soil and/or fertilizer) is reduced due to poor crop cultural practices, lack of appropriate cultivar, sub-optimal yields and N losses or deficiency of other nutrients. However, little is known about traits that contribute to differences in land races and hybrids for their performances and the adaptive mechanism of N utilization on sandy soils in a high risk environment. A three-year study was conducted to examine the N use efficiency of three cultivars: hybrid NAD-1, and improved lines Sepan82 and IRAT 204 at different N levels to identify their specific characteristics and appropriate management systems to enhance productivity. Three cultivars differed in N extraction capacity from soil indigenous N, where external N was not applied. At 90 kg ha−1 N and above, NAD-1 was more efficient in biomass production and grain yield than the two improved lines which were selected from land races, but biomass yields were similar. NAD-1 had higher N use efficiency as measured by partial factor productivity (increase in yield per unit applied N) compared to Sepan82 and IRAT 204. However, differences in agronomic efficiency, N recovery efficiency, physiological efficiency and biomass production efficiency did not differ significantly among cultivars. Harvest index and improved N uptake in NAD-1 were associated with high grain yield compared to Sepon82 or IRAT 204. Chlorophyll content of leaves estimated by a chlorophyll meter generally determined leaf N status up to 180 kg ha−1 applied N. This may have potential as a management tool since optimum N application in the degraded Sahelian soils of West Africa and use of superior cultivars such as hybrids are extremely important in determining potential productivity.

EFFECTS OF NITROGEN AND PHOSPHORUS SUPPLY ON HEXADECANE BIODEGRADATION IN SOIL SYSTEMS

The biodegradation of hexadecane (C as hexadecane-C) was assessed under 34 different external nitrogen (N supplied as NO3-N) and phosphorus (P supplied as PO4-3-P) supply conditions in order to determine how different nutrient formulations affected nutrient limitation conditions during degradation. CO2 production yields indicated that shifts in N and P supply levels resulted in variable biodegradation responses due to shifts in the limiting-nutrient (e.g., from N to P). For example, the estimated maximum fractional CO2 yield ratio was 0.24 (mg CO2-C produced mg-1 hexadecane-C) for P-limited nutrient formulations (P:hexadecane-C<0.01), whereas the yield ratio was more than two times greater when the system was not P- limited. Similar effects were observed for N-limited (N:hexadecane- C<0.15) versus non-N-limited formulations. The relative bioavailability of natural soil-N and soil-P also was examined. In the soil studied, background soil-N was 96.3% organic-N and was found to be largely nonbioavailable. In contrast, high CO2 yields were observed even when no external P was supplied. An iterative mathematical procedure indicated that the Olsen soil-P subfraction (inorganic soil-P plus soluble organic soil- P) best approximated bioavailable soil-P for this soil. Our results indicate that both N and P additions affect biodegradation yields, but that stoichiometrically inappropriate nutrient mixes produce suboptimal CO2 yields. We also found that the bioavailable fractions of soil-N and soil-P should be incorporated into estimating the most suitable nutrient formulations for a given contamination scenario.

Nitrogen Use Efficiency of Split Nitrogen Applications in Soft White Winter Wheat

AbstractNitrogen use efficiency (grain weight per unit of N supplied from soil or fertilizer) can be reduced by overfertilization, suboptimal yields, and N losses. Nitrogen is typically fall‐applied in eastern Washington for soft white winter wheat (Triticum aestivum L.) production, and is therefore subject to overwinter losses or accumulation in deep soil layers. Increasing grain protein levels of soft white winter wheat have been attributed in part to excessive N application rates and high residual N levels. Spring N applications were evaluated over four site‐years as an option to all‐fall applied N for reducing N inputs and improving N use efficiency, thereby allowing producers to maintain productivity while controlling grain protein. Five to six N rates ranging from 0 to 140 kg ha−1 for the all‐fall N applications were compared with fall‐spring split applications of 84 to 140 kg total N ha−1. Nitrogen was applied in the spring by topdressing (TD) or with a spoke‐wheel point‐injection (PI) system. A 15N experiment was conducted at two locations during the second year to quantify N uptake from fertilizer and soil N. High preplant residual N conditions resulted in limited responses to added N. Nitrogen use efficiency was 26 to 44% lower in the 140 kg ha−1 fall‐applied N treatments than in the zero‐N control. Reduced N use was related to N losses from the system and to decreased N utilization efficiency (grain weight produced per unit plant N). Spring‐applied N, with point injection or topdressing, maintained or increased N use efficiency compared with equivalent all‐fall N rates of 84 and 112 kg N ha−1. More 15N‐labeled fertilizer (7–16% more) was recovered with a split N application than with fall‐applied N at the same total rate of 112 kg N ha−1. At maturity, 68% of plant N was from soil sources with a split application, compared with 80% with an all‐fall application. These results suggest spring‐N applications with point injection or topdressing can improve fertilizer N recovery and N use efficiency over preplant applications in dryland winter wheat.

Vaccine manufacture at the time of a pandemic influenza.

In the event of a major influenza epidemic, the availability of a potent and safe vaccine would be a major concern. The following presentation describes the main features of a flu vaccine manufacturing campaign: beginning with the supply of embryonated eggs, in which the flu viruses are cultivated, through the different steps of vaccine production - egg harvest, purification, inactivation, splitting - down to the final vaccine formulation and aseptic filling in the appropriate containers. In usual times, such a production cycle takes over 70 weeks. In an emergency situation, the manufacturers and the authorities would have to take innovative approaches to minimize such delays. This will inevitably translate into an enormous strain on all the players in such a project, from the egg suppliers to the organisers of the vaccine dispatching and administration. It will result in suboptimal yields and costs. However, facing a massive and urgent need of vaccine, both the authorities and the vaccine manufacturers must work together to supply the necessary doses in time.

Simple Size-Structured Models of Recruitment and Harvest in Pacific Salmon (Oncorhynchusspp.)

Growing evidence suggests that in Pacific salmon (Oncorhynchus spp.), components of reproductive success besides fecundity are size dependent. However, managers setting escapement goals usually estimate reproductive potential of a stock in terms of total number of spawners, number of female spawners, or potential egg deposition given a mean size of spawners. Interannual variation in size composition of spawners may thus result in errors in assessing reproductive potential. Here, we develop models of recruitment and harvest and determine optimal size-selective harvesting strategies. These optimal strategies range from the current large-fish harvests (larger-than-average fish are caught, leaving smaller fish to spawn) to small-fish harvests, where the reverse is true. If the body mass (M) of individual spawners increases more rapidly than reproductive success (RS) with respect to increasing length of adult females (e.g., if number of eggs alone best measures RS), then sustainable biomass yield is maximized by the current large-fish harvest. However, if RS/M increases with increasing length of females (e.g., if total biomass of eggs best measures RS), then small-fish harvest maximizes sustainable yield. Evidence suggests that some salmon populations show this latter pattern; thus, large-fish harvests may generate suboptimal yields.

Irrigation scheduling under a limited water supply

The problem of scheduling irrigation at weekly intervals for a single crop when water supply is limited is considered. The mathematical formulation is based on a dated water-production function, weekly soil-water balance, and a heuristic assumption that water stress in the early weeks of a crop-growth stage leads to suboptimal yields. The allocation problem is solved at two levels, growth stages, and weeks. At the first level, the dated water-production function is maximized by dynamic programming to obtain optimal allocations for growth stages. At the second, the water allocated to each growth stage is re-allocated to satisfy weekly water deficits within the stage in a sequential order, beginning with the 1st week of the stage. Water delivery and soil-water storage constraints are included at both levels. The model is applied to a field problem to derive weekly irrigation programmes for cotton under various levels of seasonal water supply and initial soil moisture.

The Price of Knowledge: Fisheries Management as a Research Tool

One of the side effects of fisheries management is the discovery of new scientific information. Since this information has economic value, in that it can be used to improve future management of the fishery, the information that can be gained through a particular management strategy should not be ignored in evaluating that strategy. This paper shows using a simple model, how the research component of fisheries management can be measured and used to plan an optimal strategy. The management objectives are taken to include avoidance of risk and maximization of yield. The results depend critically on the time horizon for management. Long-term management favors creative risk-taking and leads to optimal future exploitation, while management based on short-term considerations may freeze the fishery in a permanent pattern of suboptimal yields. Key words: fisheries management, optimal control