Modelling water, nitrogen, and crop yield for a long-term fallow management experiment

Abstract

Two models that differ markedly in how they represent the crop-soil system have been used to simulate soil processes and crop production in the long-term experiment at Hermitage Research Station, Warwick, Queensland. The experiment was designed to examine the effects of tillage, stubble management, and nitrogen (N) fertiliser on the productivity of a winter cereal-summer fallow cropping system. it commenced in 1968 and the treatments have been maintained until the present. CENTURY operates on a monthly time step, considers all soil N transformations to occur in a single soil layer, and has a very simple crop growth routine that does not deal with crop phenology. APSIM provides a framework whereby a model of a cropping system is configured from component modules, which operate on a daily time step. For simulating the Hermitage experiment, modules to represent the dynamics of soil-water, N, surface residues, and growth of a wheat crop were used. The water and N modules deal with a multi-layered soil, whilst the wheat module develops leaf area, intercepts light, and accumulates and partitions dry matter in response to weather, soil-water, and N. Both models were specified to simulate the whole experimental period (1969-92) as a continuous run. The ability of these models to simulate grain yields, soil-water and drainage, nitrate-N, and soil organic matter were examined. Both models predict, in agreement with the observed data, that for this continuous cereal cropping system there has been a decline in soil organic matter for all the treatments and a reduction through time in the capacity of the soil to mineralise and accumulate nitrate during the fallows. CENTURY performed better than APSIM in predicting the relative yields of the N treatments but was less satisfactory than APSIM for absolute grain yield, soil-water, and drainage. Yield predictions with APSIM were sensitive to carry-over errors in the water balance from one season to the next, so that in some seasons large errors occurred in the predicted relative yields. Both models reproduced the observations well enough to indicate their suitability for providing useful insights into the behaviour of cropping systems where the focus is on depletion of soil fertility.

APSIM's water and nitrogen modules and simulation of the dynamics of water and nitrogen in fallow systems

“…Long-term changes in soil organic matter content is a major issue for sustainable farming systems. Probert et al (1995) provided some evidence that both SOILN and CENTURY predicted the decline in soil organic matter content that occurred in a continuous cereal cropping system with different fertilizer inputs and tillage/residue managements, but the model performance in terms of soil organic matter for other farming systems remains to be evaluated.…”

Simulating lupin development, growth, and yield in a Mediterranean environment

“…The lupin module has been based on the APSIM-Legume template described by Robertson et al (2002a). The soil water, soil nitrogen (N), and residue modules have evolved from the experience in Australia with the CERES models (Jones and Kiniry 1986) and the PERFECT model (Littleboy et al 1992), and are described by Probert et al (1995Probert et al ( , 1998. These 3 modules have been extensively tested in south-western Australia in conjunction with the APSIM-Wheat (Asseng et al 1998) and APSIM-Canola (Farré et al 2002) modules.…”

Dynamic replacement and loss of soil carbon on eroding cropland

“…Fragipan development and loss occur over millennia, and the depth to the fragipan is thought to be about 80-100 cm in undisturbed, uneroded soils of the region. In agriculturally eroded conditions, the depth of the fragipan can be less than 40 cm deep [Rhoton and Tyler, 1990]. We use the soil volume above the fragipan as a measure of total soil lost since cultivation and compare this estimate to the cumulative sum of erosion estimated from annual sediment yields in watershed and weir studies.…”