Modelling and measurement of the effects of fertilizer‐N and crop residue incorporation on N‐dynamics in vegetable cropping

Abstract

An easy-to-use simulation model was developed with the aim of improving fertilizer practice when crop residues are incorporated instead of removed. It was tested against data from a well-monitored N fertilizer experiment in which three successive brassica crops were grown followed by barley. Experimental findings included: (a) that fertilizer-N greatly increased yield of 3 crops without increasing residual soil mineral-N at harvest unless supply exceeded crop demand; (b) that, by contrast, fertilizer-N increased both yield of and residual soil mineral-N left by the remaining crop throughout the range of applications; and (c) that at each harvest the apparent disappearance of fertilizer-N by immobilization and other processes was almost proportional to fertilizer-N. These phenomena were simulated by the model. Overall the model gave estimates of soil mineral-N, plant weight and O/ o N in the crop for each crop that were either in close agreement with or linearly related to the measured values. Deviations from this pattern are shown to result almost entirely from experimental error. In addition the model gave simulations of the time course of soil mineral-N and soil water that were in good agreement with measurement.Simulations with the model indicate that appreciable benefits from residue incorporation of crops will only be obtained when fertilizer-N is also applied, unless plant masses at harvest are small.

Aspects of nitrogen use efficiency of cauliflower II. Productivity and nitrogen partitioning as influenced by N supply

“…Direct measurements of N translocation using isotopes (Ma et al 1998) with high temporal resolution may be used to further substantiate the estimates presented in the present paper. The low nitrogen harvest index (Figs 2 and 5) of cauliflower observed in the present study is in accordance with other data from the literature (Rahn et al 1992;Greenwood et al 1996;Van den Boogaard & Thorup-Kristensen 1997). Low values of N harvest index are common for vegetable crops where immature generative organs are harvested, like brussels sprouts (Booij et al 1997) and broccoli (Bowen et al 1999).…”

A dynamic model for the combined effects of N, P and K fertilizers on yield and mineral composition; description and experimental test

“…The model required the maximum value of W at final harvest, the starting value of W, the average daily air temperature, rainfall and pan evaporation and the soil characteristics given in Table 2. The N mineralization rate, calculated from soil organic matter and clay contents after Ruhlmann (1999), was 0.7 kg N ha −1 d −1 at 15.9°C, and was in agreement with previous measurements on this soil (Greenwood and Draycott 1989a, b;Greenwood et al 1996). The model assumed that mineralization rate Simulations of soil mineral N were started on the 1st October in the year before that in which sowing and planting took place.…”

Dissolved nitrogen model for paddy field ponded water during irrigation period

“…Nitrogen transport models are generally composed of nitrogen transformation and water movement submodels. Various nitrogen transformation models for farmlands have been proposed (Bergstrom et al 1991;Bradbury et al 1993;Greenwood et al 1996;Shiratani et al 1997;Pang and Letey 1998). Although these models can represent complex nitrogen changes in farmlands, dealing directly with the nitrogen concentration in water ponded on a paddy field is difficult with these models.…”