J. Beltrão

The effect of salinity on corn yield using the CERES-maize model

In most cases, when calculating soil water availability, only thewater content is considered. The effect of salinity on the wiltingpoint is neglected. The objective of this work is to use asimulation model (CERES-maize) in order to predict cornyields as a function of water salinity under severalenvironmental, agrotechnical, and plant characteristics. A modelis presented in which the wilting point is a function of the soilsalt content. At high salinity, the water content at wilting pointis higher than at low salinity, resulting in an insufficient amountof available water and, therefore, a reduced yield. The modelwas used to simulate several theoretical and experimentalsituations for forage corn and grain corn. Simulation resultsshowed that nitrogen fertilization increases the salinity thresholdvalue and the yield sensitivity (rate of yield reduction per unitof salinity). The also showed that forage corn is more sensitiveto salinity than grain corn. If the soil is not leached, a heaviersoil texture has a higher salinity threshold value. On the otherhand, if the soil is leached, the soil texture has no influence onthe salinity threshold value and the yield is less sensitive tosalinity in sandy soils. The determination coefficient (r2= 0.75) indicated that the results of the simulations were in goodagreement with the field data.

Grass response to municipal wastewater reuse as compared to nitrogen and water application

Bermuda grass (Cynodon dactylon, L. Pers) is used very often in the fairways of golf courses, due to its tolerance to drought, high temperatures and treading damage. The objective of this work was to study the response of this grown cultivar with Dallis grass (Paspalum dilatatum, Poiret), to several levels of municipal wastewater. An experimental setup known as sprinkle point source was used to simulate the various levels of water application, expressed by the crop coefficient kc and the crop evapotranspiration rate. Results were compared with those obtained for sprinkle irrigated plots under nitrogen fertilization. At lower water application rates (kc 1), grass yield response to wastewater was comparable to potable application combined with nitrogen application between 0 and 25 kg ha−1.month−1. Visual appearance of the lawngrass was good for kc values > 1.2, when wastewater was applied.

Soil pollution by nitrates using sewage sludge and mineral fertilizers

With the objective of evaluating soil pollution by nitrates, due to nitrogen leaching, several treatments using urban sludge and two mineral nitrogen fertilizers — ammonium sulfate applied as basic fertilization and potassium nitrate, applied by fertigation — were applied to fertilize cucumber plants (Cucumis sativus, L.). An alluvial soil was used; pH was 7.9 and its organic matter content was a middle value. Using fertigation (potassium nitrate), the best yield and the highest nitrogen use efficiency were obtained and only an insignificant amount of nitrogen was leached. Amounts of ammonium sulfate of 3.5 ton.ha−1 were toxic to the plants, and their nitrogen use efficiency was about 10%. On the other hand, the urban sludge treatment showed a nitrogen efficiency of 45% and there was practically not any nitrogen loss by leaching.

Modeling the effect of capillary water rise in corn yield in Portugal

There are regions in Europe such as Italy, Portugal, or Holland in which capillary water rise plays an important role in crop water regimes. The objectives of this work were: to modify an existing simulation model (CERES-maize) by including a capillary rise submodel; to use it for predicting the production function of corn grown above a shallow ground water table; and to compare model prediction with experimental results in Portugal. It is assumed that the capillary rise determines the initial conditions of soil water profile within the root zone, just before the sowing day. The model was used to simulate several theoretical and experimental situations for forage corn. Simulation results showed that the production function reaches an optimal yield when the best combination of soil, air and water is obtained. Capillary rise has a negative effect on yield, at high irrigation level. At low irrigation level, the best combination of air and water was obtained when ground water table depth was about 1 m below surface. The good determination coefficient (r2=0.92) indicated that results of simulations were in good agreement with experimental results. It is concluded that upward flow from shallow water is a significant component in the irrigation water balance of corn.

Sewage sludge as a horticultural substrate

This work aims to justify of the use of urban sludges, mixed with either fertilized or unfertilized peat, through the study of their effects on the germination and growth of a Pelargonium hybrid as well as effects on substrata and plant pollution (pathogens). Several treatments of urban sludges mixed in varying proportions with fertilized or unfertilized peat were used. Germination rate in all instances was above 70% and reached 100% for 3 treatments. Plant growth (height) and leaf production were generally better when fertilised peat was used in mixtures but plant height also equalled the maximum when grown in pure urban sludge. Chemical and microbiological analysis of the different treatments showed that there was not any potential pollution hazard for the use of this urban sludge as a substrate.