Nitrogen (N) is the most important nutrient in maize production and its availability can affect the production potential of maize. Availability of nitrogen in soil largely varies with place and time. Models are some of practical methods used to evaluate and monitor availability and impact of nitrogen on maize production; APSIM is one of such models. APSIM has several modules that have different functionalities and one of such modules is SoilWat module. The study modified SoilWat module by incorporating Nitrogen Distribution model. Trial and error method was used in the calibration of the nitrogen distribution model that was incorporated in the APSIM model as subroutine. The initial values of nitrogen distribution were obtained from literature and these values formed the basis for development of the model. After development of model using parameters obtained from literature review, field experiment was conducted to collect data to be used in redefining the model. The simulated nitrogen distribution was compared with values obtained from the field experiment and their mean differences were initially high but the process was repeated until the mean difference was small. In field experiment, the study had two factor, each with four regimes. The Triscan Sensor (EnviroScan, Sentek Pty Ltd, Stepney, Australia) was used to measure total nitrogen concentration at lateral distances and vertical depths. Primary soil samples were collected and analysed at Bunda College Laboratory. The study inferred that Soil water percolates down to underlying layer only when proceeded layers are satisfied i.e. has reached its field capacity, above which excess water is left free to percolates down the soil profile. Before water arriving in last layer it had to satisfy the above-lying soil profiles. The study has shown that increase of nitrogen contents in underlying layers corresponds with decrease of the same in top layers due to advection movement. Consequently, the increases of soil water in a specific layer correspond to decrease of nitrogen content in that particular layer. The study has shown that APSIM under predicted during the latter stage of the maize growing season and over predicted in the early stage of the growing season, and it overestimates soil water contents in soil profile.

There are several models that monitor movement of nitrogen in the soil. Most of these models have not been widely used in southern Africa because of sophisticated equipment required to collect data and the data needed to run the model are intensive. Nitrogen Distribution Model (NDM) has been developed to ensure that it responds to increasing need of managing nitrogen in agricultural systems characterized by smallholder farmers who do not have adequate resources to collect intensive data for modeling. NDM has parameters that are explicit and mostly intuitive and maintains good balance of simplicity and robustness. With the nature of smallholder farming in Malawi where over 85% of population are rural-based smallholder farmers, the model has also be designed so that it can acts as database to keep track of farmers and farms so that were given farm-specific nitrogen and water management advice.

Soil moisture availability to plant roots is very important for crop growth. When soil moisture is not available in the root zone, plants wilt and yield is reduced. Adequate knowledge of the distribution of soil moisture within crop's root zone and its linkage to the amount of water applied is very important as it assists in optimising the efficient use of water and reducing yield losses. The study aimed at evaluating the spatial redistribution of soil moisture within maize roots zone under different irrigation water application regimes. The study was conducted during two irrigatation seasons of 2012 at Nkango Irrigation Scheme, Malawi. The trials consisted of factorial arrangement in a Randomised Complete Block Design (RCBD). The factors were water and nitrogen and both were at four levels. The Triscan Sensor was used to measure volumetric soil moisture contents at different vertical and lateral points. The study inferred that the degree of soil moisture loss depends on the amount of water present in the soil. The rate of soil moisture loss in 100% of full water requirement regime (100% FWRR) treatment was higher than that in 40% FWRR treatment. This was particularly noticed when maize leaves were dry. In 100% FWRR treatment, the attraction between water and the surfaces of soil particles was not tight and as such "free" water was lost through evaporation and deep percolation, while in 40% FWRR, water was strongly attracted to and held on the soil particles surfaces and as such its potential of losing water was reduced.

Nitrogen (N) is the most important determinant nutrient for plant growth and crop yield. Plants lacking N show stunted growth and yellowish leaves. Plant growth and crop yield usually increase when N is added. However, too much N leads to weak stems in grain crops (lodging) which result into low yield. The aim of the study was to delineate changes of N concentration, its direction of movement and its pattern of disposition in the soil as influenced by amount of applied water and nitrogen so as to reduce N losses and maximise its absorption by maize roots.The study was conducted during irrigation seasons of 2011 and 2012 at Nkango Irrigation Scheme, Malawi. The trials consisted of factorial arrangement in a Randomised Complete Block Design (RCBD). The factors were water and N and both were at four levels. The Triscan Sensor was used to measure total N concentration at different vertical and lateral points. The study inferred that changes of N concentration, its direction of movement and its pattern of disposition in the soil are influenced by water flux and absorption rate of plants roots due to gradient created by absorption. The study noted that when N is in low supply, its movement towards maize roots is greatly influenced by diffusion. The study concluded that to maximise N absorption by maize roots, the point of N application should be at 5 cm away from the planting station to minimise N losses through drifting away from the maize rooting zone.