José Geanini Peres

Evaluation of the effects of sugarcane straw coverage in moisture and water loss of soil.

In the period from June 23 to July 23, 2006, in the regional environment of Araras-SP, it was studied the influence of sugarcane straw coverage harvested mechanically in water content of a dystrophic dark-red Latosol, A moderate and clayey texture. The variation of volumetric water content of soil in these plots was assessed in layers of 0 to 0.20 m and 0.20 to 0.40 m deep. The experimental treatments consisted of covering the soil with quantities of sugarcane straw equivalent to 0 and 1.5 kg.m-2 (0 and 1.5x104 kg.ha-1), the first representing the condition without straw and the second condition with straw . The results collected in the 0-0.20 m layer showed that during the study period there was a decrease in soil water content of 0.103% per day provided with straw and 0.223% per day without straw, or more than double the water loss recorded previously. When it was considered the soil layer of 0.20-0.40 m, the decrease in soil water content was much lower than that of the previous situation, the order of 0.116% per day provided with straw and 0.159% per day without straw. An important point to note is that the treatments used in the experiment had a decisive influence on the direction of water movement in the soil.

Utilização de lisímetros de pesagem para a determinação dos coeficientes de cultura do meloeiro (Cucumis melo L.) para cultivo em estufa agrícola na região de Araras - SP

The research was conducted in a greenhouse installed at the experimental farm of the Center for Agrarian Sciences, Federal University of Sao Carlos, in the city of Araras - SP. The soil of the experimental area is dark red Latosols, dystrophic; moderate A horizon, clay texture. The melons studied were the hybrids Louis and HD 90. The experiment was irrigated by drip irrigation and control accomplished through two weighing lysimeters installed inside the greenhouse. Soil moisture was monitored with a TDR probe and maintained close to field capacity. The climatic information was collected in automatic weather stations installed inside and outside the greenhouse. The reference evapotranspiration (ETo) was estimated by the Penman-Monteith, Penman, Makkink and Class A Pan models. The water consumption measured in the lysimeters was 254.5 mm and 188.6 mm, respectively, for melons Louis and HD 90, corresponding to an average daily consumption of 3.18 mm and 2.35 mm. All models underestimated the ETo estimated by the standard model of Penman-Monteith varying from a minimum of 26.9% in the case of the Penman model up to 74.3% in the Makkink model. The crop coefficients determined by the standard model of Penman-Monteith, here considering the average value of the two types of melon studied, were as follows: early stage: 0.20; intermediate stage: 1.10 and final stage: 0.50.

Wetted Soil Volume as a Design Criteria in Drip Irrigation

The principal objective of a drip system design is to choose the appropriate layout and components to obtain adequate soil solution distribution throughout a field. In addition to maximizing crop production, modern fertigation practices must consider environmental sustainability and rigorous water management. These often conflicting considerations require significant changes in irrigation system design and operation (relative to traditional designs for maximum crop production). We conducted experiments to characterize dynamics and patterns of soil solution within the wet bulbs formed by drip fertigation for pepper (Capsicum annum, L). Time domain reflectometry (TDR) probes were used to monitor the distribution of potassium nitrate (KNO3) and water distribution from drippers discharging at constant flow rates of 2 and 4 L h-1 under field conditions. Considering results from different profiles, it was observed greater (large) solute storage near the dripper decreasing gradually towards the wetting front. About half of the applied KNO3 solution (65%) was stored in the first layer (0-0.10 m) for all experiments and 22% was stored in the next layer (0.10-0.20 m). Comparing different dripper flow rates higher solution storage was found for 4 L h-1 by means of 72% of applied KNO3 solution was accumulated in the first layer (0-0.10m) compared with 60% for 2 L h-1. The chemical analysis of leaf showed no differences between N and K concentrations for different flow rates. These results suggest that based on the volume and frequency used in this experiment, it would be advantageous to use flow rate of 4 L h-1 to reduce deep percolation losses of applied water and solutes.