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To assess the impact of land use on the Andosol fertility, changes in chemical and physical properties affecting soil quality were monitored on Andosols from Mount Bambouto submitted to four different land use and management systems: natural cover, tillage, burning and fallow. In comparison with the natural cover, tillage reduces Andosol OC (6.5 to 4.8%), total N (4.51 to 2.95‰), CEC (22.0 to 20.9 cmol.kg^–1) and the abundance of soil macro-aggregates expressed by the water stable aggregates (WSA) varies from 53.8 to 12.0%; and increases the bulk density (0.69 to 1.09 g.cm^–3) and the sum of exchangeable cations (3.58 to 4.84 cmol.kg^–1). Burning also reduces Andosol OC (6.5 to 0.8%), total N (4.51 to 0.95‰) and CEC (22.0 to 10.2 cmol.kg^–1), but increases soil pH (4.62 to 6.54), the sum of exchangeable cations (3.58 to 5.74 cmol.kg^–1) and the abundance of soil macroaggregates (WSA: 38.2 to 57.0%). In comparison with tillage, fallow increases Andosol OC (4.8 to 6.5%), total N (2.95 to 5.04‰), CEC (18.0 to 21.6 cmol.kg^–1), the sum of exchangeable cations (3.58 to 5.05 cmol.kg^–1) and the abundance of soil macroaggregates (WSA: 12.0 to 48.8%). Globally, the tillage management deteriorates Andosol chemical and physical properties affecting fertility, whereas the fallow management restores them. The burning management also improves some Andosol chemical and physical properties affecting quality, but it won’t last long

For estimating N losses in soil‐crop systems with the simple and functional CERES models, we evaluated their N modules and compared them with the more complex SLIM (for solute transport) and NCSOIL (for N mineralization) models. SLIM is based on the concept of immobile and mobile water regions in soil, and CERES on a piston‐flow hypothesis. In NCSOIL, the soil organic matter (SOM) mineralizes through two active pools, whereas in CERES the SOM decomposes as a whole with a gross decay rate. We used data on mineral N dynamics under bare soils (silt loam, loam, and sandy loam) from 1‐yr‐long experiments at three locations in France, including measurements of weekly NO3 leaching fluxes. The original CERES mineralization submodel did not correctly simulate N supply from potentially degradable SOM. When using NCSOIL instead, the simulations improved and CERES predicted NO3 leaching reasonably well, with a root mean square error of 6 to 21 kg N ha‐1, representing 5% of the yearly flux. The SLIM model performed as well, and better simulated the intense NO3 percolation regime that occurred in wintertime. Its immobile water fraction parameter had to be calibrated, however, or the yearly leaching flux was underestimated. When linked to NCSOIL, the CERES model showed a good potential for estimating N dynamics in soil, even if its piston‐flow type of NO3 transfer was not always relevant. In such case, SLIM was a more appropriate approach, although it required a site‐specific calibration.

In response to a very high increase of groundwater NO−3 pollution, largely connected with intensive agricultural practices, a long‐term experimentation has been set up close to Grenoble, France, with the following aims: first to characterize the response of maize (Zea mays L.), a predominant crop in the area, to fertilization, and second to quantify the N balance during and after the crop cycle. This study relates to results concerning the second issue; experiments were conducted on irrigated maize in 1991, 1992, and 1993 on the Experimental Farm at La Côte Saint‐André, France, in the heart of one of the most important agricultural zones between the French Alps and the Rhone Valley. The dynamics of soil and fertilizer N (NO−3 transport and N balance during cropping and intercropping periods) were continuously monitored using 15N isotopic tracing and the tensio‐neutronic method (i.e., continual measurement of soil water balance using a neutron moisture meter and tensiometers), together with porous suction cups installed at 0.3‐, 0.5‐, and 0.8‐m depths. Water drainage and leaching of NO−3‐N, with a partition between that derived from fertilizer and that produced by soil mineralization, were thus obtained during and after the crop cycle. The balance of the labeled fertilizer at harvest was also determined by conventional soil coring and plant sampling. The two methods were used successfully during the 3 yr in which there were different climatic conditions and different fertilizer application rates. The results show that the traditional fertilizer input in the area (260 kg N ha−1) could be reduced nearly 30% without any substantial loss in grain yield but with a considerable reduction of nonpoint source pollution due to NO−3 leaching. It is also shown that with the combined use of the two methods, it is possible to characterize separately fertilizer‐N uptake, fertilizer‐N leaching, and N immobilization and to estimate N‐gaseous losses.

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ABSTRACT:Knowledge of moisture content is crucial in assessing spatial and temporal movement of water through the unsaturated zone. Moisture storage is also important for monitoring the soil water balance and for validation of water balance models. The purpose of this work was to determine and analyse moisture content profiles at point locations in the unsaturated zone of a lateritic soil around Nsimi, south of Cameroon. Neutron probe has been connected to a set of tensiometers in an area of 60 ha. A comparative study between a site covered with vegetation and a site uncovered was conducted to assess the influence of vegetation in the process of moisture transfers. The results showed that the spatial distribution of moisture profiles varied according to the site and the texture of the soil, with in general increasing of moisture from the surface horizon toward the deeper layers. The mean values of moisture varied from θ m = 0,397 cm 3 /cm 3 on barren site, against θ m = 0,429 cm 3 /cm 3 in vegetation. Values of suction were generally strong in surface and at depth, but weak in the intermediate layers.