Processing tomato is an important crop in California, where ≈ 100,000 ha is grown annually. In the past, processing tomatoes have been irrigated mostly by sprinkler and furrow irrigation, although several tests have been conducted with drip irrigation, and a few growers are using subsurface drip irrigation. Yields of tomato have been shown to be sensitive to water management when the amount of irrigation water closely matches plant water use. Tomatoes have been identified as susceptible to drought stress and waterlogging at both ends of the furrow irrigation cycle. Subsurface drip irrigation is a relatively new method in which drip irrigation laterals are buried permanently 20 to 60 cm below the soil surface. This method has provided the control and uniformity of water and fertilizer distribution necessary to maximize the yield of processing tomatoes. A computerized control system maintains nearly constant soil water and nutrient concentration in the root zone by irrigating and fertilizing frequently, thus avoiding small water and nutrient stresses, especially during the critical period between first and peak bloom. During the maturation and ripening stage, irrigation and nutrient concentrations can be adjusted to increase soluble solids and to adjust the maturation rate to coincide with the harvest schedule. Maximum yield levels can be obtained when nearly all the fertilizers (N, P, and K) are injected precisely in time and space through the drip irrigation system to meet the crop nutrient requirement. Water-use efficiency (WUE), defined as the ratio of yield: unit of water used by the plant, can be maximized by using this precise irrigation and fertilization technique. Yields >200 t·ha-1 of red tomatoes were achieved in large field plot research, and commercial yields of 150 t·ha-1 were achieved in large-scale field applications with a lesser degree of control. Therefore, we predict that with further fine-tuning, commercial yields of 200 tons of processing tomatoes/ha could be achieved using a subsurface drip irrigation system with accurate water and fertility management.
Variable lengths of water deprivation immediately prior to harvest were imposed on mature French prune trees for four consecutive years. Irrigation cutoff durations were about 45, 37, 30, 22, 17 and 12 days prior to harvest during 1986-89.
Predawn leaf water potential best reflected water deprivation length and reached minimum values of about -1.5 MPa with the most severe cutoff. Magnitude of peak stomatal conductance was reduced and occurred earlier in the day with longer cutoff regimes.
Rate and time-course development of preharvest fruit drop was variable from year-to-year, but there were no significant differences in total drop between cutoff treatments. Only in the fourth year, following three years of no difference were tree fruit load and yield significantly reduced but then only with the most severe cutoff. Soluble solids were higher and drying ratios lower with the longer cutoffs. Fruit size was significantly reduced in the third year of the experiment. Trunk circumferences were significantly lower only with trees subjected to the longer cutoff regimes.
Field studies were conducted on a Typic Xerorthents Entiosols soil (Hanford sandy loam) to determine the response of two cultivars of processing tomatoes (Lycopersicon esculentum Mill.) to trickle irrigation applied at three percentages of evapotranspiration (ET) to either the top of the plant row or between the beds using a traveling irrigation system. Irrigation was terminated when fruits were either 30% or 70% red (14 or 7 days before harvest). Yields of red tomatoes and total tomatoes increased with increasing trickle irrigation water. The concentrations of soluble solids (SSC) and total solids (TS) and pH decreased with increasing trickle irrigation rates, while color, fruit size, and acidity increased, as did the yield of SSC and TS per hectare. Placement of trickle irrigation on the plant row was more favorable than placement in the furrow between the beds for yield and quality characteristics. Trickle irrigation to 70% ET terminated 7 days before harvest produced responses similar to conventional furrow irrigation. Although statistically these treatments could not be compared directly to conventional furrow, all traveling trickle irrigation rates were superior in water use efficiency to that of the conventional furrow irrigation. Trickle irrigation rates of 35% ET, 70% ET, and 105% ET did not differ in water use efficiency. Chemical names used: 2(a-naphthoxy)-N,N-diethyl propionamide (napropamide); S-propyl butylethiocarbamate (pebulate).
Root length densities (cm·cm−3) of ‘VF145-B7879’ and ‘UC-82B’ tomatoes (Lycopersicon esculentum Mill.) were determined at three depths and four locations across the planting bed for traveling trickle irrigation treatments applied at 35%, 70%, and 105% of evapotranspiration (ET). Cultivars did not differ in root length densities or in their effect on soil moisture levels. Root length density and soil moisture decreased with soil depth. Although soil moisture was greater in the furrows, the zones of highest root concentration were between the rows of plants and along the edge of the beds. Greater root length density was found in the 35% ET than in the 70% or 105% ET irrigation rate. Chemical names used: 2-(α-naphthoxy)-N,N-diethylpropionamide (napropamide); S-propyl butylethylthiocarbamate (pebulate).