Testing the APSIM model with data from a phosphorus and nitrogen replenishment experiment on an oxisol in

Abstract An experiment was conducted on an Oxisol near Maseno in western Kenya, to compare the growth of maize crops to inputs of two phosphorus sources. Commercial triple superphosphate (TSP) and Minjingu phosphate rock were applied either at a once-only rate of 250 kg P ha -1 or as five annual inputs of 50 kg P ha -1 . The experiment was carried out over 10 cropping seasons between 1996 and 2000. An additional factor studied was the source of N, either as urea or tithonia biomass-N to supply 60 kg N ha -1 . Both N and P sources were applied only to the crops grown in the long rain season. The APSIM model has been tested against this data set. The effects of P treatments were large in the long rain season, but in the short rain season the inadequate supply of N greatly reduced growth and P effects. The yields of the maize crops were predicted well (r 2 = 0.88) with respect to both the P treatments (as TSP) and the N inputs (as urea). The predicted water, N and P stresses were informative in understanding the contrasting pattern of response observed in the two seasons. The simulation of this long-term experiment shows that the APSIM SoilP module is robust, in as much as it extends the testing of the model to a very different environment where there were both N and P stresses affecting plant growth, and on a very different soil type to where the concepts in the APSIM phosphorus routines were originally developed and tested. Crop production on many soils in western Kenya is limited by both nitrogen (N) and phosphorus (P). The concept of recapitalisation of soil P has focused attention on the use of rock phosphate materials rather than commercial forms of processed fertilisers, and the feasibility of raising soil P through large, one-time application rather than a gradual increase with smaller, but regular inputs . Such strategies have been evaluated in long-term experiments in western Kenya. Probert In this paper, we describe the testing of the APSIM P routines using an experiment that provides suitable data for testing some aspects of the model. The annual rainfall and soil type, especially with regards to its phosphorus sorption properties, ar

Modelling nitrogen mineralization from manures: representing quality aspects by varying C:N ratio of sub-pools

The mineralization/immobilization of nitrogen when organic sources are added to soil is represented in many simulation models as the outcome of decomposition of the added material and synthesis of soil organic matter. These models are able to capture the pattern of N release that is attributable to the N concentration of plant materials, or more generally the C:N ratio of the organic input. However, the models are unable to simulate the more complex pattern of N release that has been observed for some animal manures, notably materials that exhibit initial immobilization of N even when the C:N of the material suggests it should mineralize N. The APSIM SoilN module was modified so that the three pools that constitute added organic matter could be specified in terms of both the fraction of carbon in each pool and also their C:N ratios (previously it has been assumed that all pools have the same C:N ratio). It is shown that the revised model is better able to simulate the general patterns on N mineralized that has been reported for various organic sources. By associating the model parameters with measured properties (the pool that decomposes most rapidly equates with water-soluble C and N; the pool that decomposes slowest equates with lignin-C) the model performed better than the unmodified model in simulating the N mineralization from a range of feeds and faecal materials measured in an incubation experimen

Effect of soil fertility management strategies and resource-endowment on spatial soil fertility gradients, plant nutrient uptake and maize growth at two smallholder areas, north-western Zimbabwe

We investigate the effects of smallholder farmer resource-endowment and soil nutrient management strategies on plant nutrient uptake and growth across soil fertility gradients under semi-arid conditions. Soil fertility gradients as influenced by farmers’ resource availability may affect the response of crops to fertilizer addition and therefore productivity. The study was conducted in Njelele and Nemangwe smallholder areas (450-800 mm per annum, unimodal) in north-western Zimbabwe. Soil and maize cobleaf samples were collected from fields of farmers (varying resource endowment) located near to (homefields) and far away (outfields) from the farmers’ homesteads during the 2005-6 season. The samples were analysed for selected soil fertility indicators and soil samples were further used to test maize growth response to various nutrient applications under greenhouse conditions. Soil fertility (organic C, total N and available P) significantly (P<0.05) decreased from resourceendowed to resource-constrained farmers, and from outfields to homefields, but the latter differences were only significant for available P. Besides resource-endowment and field type, response to nutrient applications also depended on soil texture. In sandy soil, both N and P were limiting to MAIZE growth in outfields while N was most limiting in the homefield. It was concluded that resource-endowment and nutrient resource management strategies employed by farmers result in soil fertility gradients which affect response of crops to fertilisation and therefore need to be factored in the development of fertiliser recommendations

Building adaptive capacity to cope with increasing vulnerability due to climatic change in Africa – A new approach

The world community faces many risks from climate change, with most scenarios indicating higher temperatures and more erratic rainfall in Africa. Predictions for southern Africa suggest a general decrease in total seasonal rainfall, accompanied by more frequent in-season dry spells that will significantly impact crop and livestock production, and hence economic growth in the region. The hardest hit will be the rural poor in the drier areas, where crop failure due to drought is already common and chronic food emergencies afflict the region in most years. Lessons can be learnt on how the rural poor currently cope with the vagaries of climate and these can be used to help them adapt their current production systems to the future threats of further climate change. But this assumes the institutions that work towards the economic empowerment of the rural poor have the requisite skills to understand their current coping strategies and how adaptation can be facilitated. A new initiative led by Midlands State University and the Zambian Meteorological Office proposes that improving the ability of institutions that train the ‘Future Change Agents’, who will subsequently support smallholder communities in adapting their agricultural practices to current climate variability, is the first step in building adaptive capacity to cope with future climate change. The capacity of African scientists, regional organizations and decision-makers in dealing with the issues of climate change and adaptation will be enhanced on a continuing basis, and the impacts of their agricultural development programs improve

The DECam Local Volume Exploration Survey Data Release 2

We present the second public data release (DR2) from the DECam Local Volume Exploration survey (DELVE). DELVE DR2 combines new DECam observations with archival DECam data from the Dark Energy Survey, the DECam Legacy Survey, and other DECam community programs. DELVE DR2 consists of similar to 160,000 exposures that cover >21,000 deg(2) of the high-Galactic-latitude ( divide b divide > 10 degrees) sky in four broadband optical/near-infrared filters (g, r, i, z). DELVE DR2 provides point-source and automatic aperture photometry for similar to 2.5 billion astronomical sources with a median 5 sigma point-source depth of g = 24.3, r = 23.9, i = 23.5, and z = 22.8 mag. A region of similar to 17,000 deg(2) has been imaged in all four filters, providing four-band photometric measurements for similar to 618 million astronomical sources. DELVE DR2 covers more than 4 times the area of the previous DELVE data release and contains roughly 5 times as many astronomical objects. DELVE DR2 is publicly available via the NOIRLab Astro Data Lab science platform

Decision support tools for site-specific fertilizer recommendations and agricultural planning in selected countries in sub-Sahara Africa

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