Evaluation of Replacement Policies in Sow Farms Using Arena^(TM) Simulation Software

This paper presents an application of the simulation of discrete events (SED) using ARENATM in the management of large-scale breeding farms. The main objective of the simulation model is to find a policy of replacement, to ensure the best economic performance of a farm. The only variant analyzed of replacement policy was the number of cycles set in permanency for a sow in the herd. Considered incomes come from the sale of piglets and unproductive sows, and costs are due to the feeding of animals, replacement sows purchases, and the operation expenses of the farm. For this analysis, the production process was divided into three major stages called: mating, pregnancy or gestation and lactation. The sow’s movement from one stage to other was modeled by cycle-dependent transition probabilities. Considering the daily utility, as response variable, the model shows the best number of cycles to maintain the sows.

Systems research helping to meet the needs and managing the trade-offs of a changing world

Facing the challenges of an increasing world population, a changing climate and ever depleting resources, agricultural intensification （Keating et al. 2010） is one of the few options for meeting the demand of food security. It is necessary to apply a dynamic and systematic approach to effectively man- age the complex agri-eco production and green processing systems. Indeed, farming systems approach for appropriate technology development and simulation modeling is a result of adopting the system thinking by the agricultural research community （Norman et al. 1995）.

Accumulation ofSOCunderorganicandno-fertilizations,anditsinfluenceon crop yieldsinTanzania’s semiaridzone

Introduction:To estimate differential accumulation of soil organic carbon(SOC)and its ecological significance is very important to smallholder farmers in the Tanzania's semiarid areas.This study investigated the accumulation of SOC and other important soil nutrients under organic and no-ferti lizations,and correlated SOC with crop yields.Using data from long-term experimental study sites of semiarid in Tanzania,we estimated SOC accumulation in different soil treatments and depths where a total of 128 soil samples were collected at the depths of 0-20 cm and 20-40 cm from two villages(sites)with organic ferilization and no-ferilization treatments.Sites under organic fertilization were defined as those which have received manure fertilization for more than 5 years on continuum basis.Outcomes:The accumulation of SOC was significantly greater in soils under organic fertiliza-tions(1.15 and 0.80 MgC ha-'at soil depth and 20-40 cm)and decreased with increa sing soil depths.Similarly,TN and P decreased from 0.40 and 2.40 Mg(0-20 cm)to 0.16 and 2.10 Mg(20-40 cm),respectively.Other important soil nutrients such as calcium(Ca^(2+)),potassium(K^(+)),magnesium(Mg^(2+)),and sodium(Na^(+))had similar patterm.In addition,soil bulk density was less under organic fertilization(1.1 g/cm^(3))than under no fertilization(1.2 g/cm^(3))and it increased with soil depths.Correspondingly,the crop yields were significantly higher(1.6 tn ha^(-1))under organic friliations than(0.6 tn ha^(-1))under no-fertilizations indicating that crop yields were significantly affected by SOC.Discussion:Organic fertilization i.e.,especially cattle manure in the area has considerable fertility potential.To optimize soil fertility potential,we need to consider such kind of ferilization from household to national level.Conclusion:Our results demonstrated that manure application was the best ferilization method for improving soil fertility in most croplands of Tanzania's semiarid areas,especially in this era of climate change scenarios.