The 2011 ASHS Annual Conference

The use of improved irrigation scheduling techniques has been shown to greatly increase irrigation water use efficiency and consequently fertilizer is retained in the effective root zone longer resulting in substantial water savings and reduction of the potential N-leaching losses. During the spring of 2008, 2009 and 2010, field experiments were conducted to test different thresholds of soil moisture sensor (SMS) based irrigation control systems for green bell pepper. Irrigation treatments were: SS₄, water application controlled by SMS-based irrigation set at 4% volumetric water content (VWC) which was allotted five irrigation windows daily and bypassed events if the soil VWC exceeded the established threshold; SS₈, threshold set at 8% VWC; SS₁₂, threshold set at 12% (soil field capacity) and TIME, control with irrigation being applied once a day similar to grower irrigation management. SMS-treatments resulted in relatively steady soil moisture content over time, because irrigation water was distributed across multiple irrigation events according to the soil moisture threshold. The SMS-based treatments irrigated for short periods of time and resulted in a relatively small increase in soil moisture, consequently decreasing the volume of percolate and NO₃-leaching. The average pepper marketable yield was 21.1; 27.7; 32.2 and 29.2 Mt/ha for SS₄; SS₈; SS₁₂ and TIME, respectively. Significant reductions in the volume of irrigation applied (12-76%) were reported when SMS controlled the irrigation compared to TIME treatment. A quadratic response between irrigation water saving and relative pepper marketable yield was observed. The response of pepper yield increased when irrigation water application was reduced. The yield plateau was reached at 25-30% of irrigation water reduction, which was obtained when SS₁₂, which was slightly above soil field capacity for the experiment site. After reaching the plateau, the yield response was reduced as water savings increased (lower setting of SS). Due to the low soil water retention capacity, additional irrigation water application above the soil field capacity resulted in excessive water percolation and nutrient leaching, although this practice did not affect the water supplied to the plant, it negatively affected the plant mineral nutrition and nitrate leaching. Pepper photosynthetic rates (PR) decreased with the increase of irrigation water saving, there was no significant differences in PR between TIME and SS₁₂ treatments, however, SS₈ and SS₄ resulted in lower PR and yield, which was associated to soil water deficit.