Water Use and Irrigation Management for Vegetables in Georgia: Solanaceae Crops

Water Use and Irrigation Management for Vegetables in Georgia: Solanaceae Crops

This publication is the third in a series on irrigation scheduling for vegetable crops. It provides basic information on water use and irrigation management using the crop water demand method for Solanaceae crops such as bell peppers, tomatoes, and eggplants.

Irrigation Scheduling

Growers have several strategies available for irrigation scheduling. One of the simplest and most precise is the crop water demand method, also known as crop evapotranspiration (ETc). Under this method, irrigation supplies the daily volume of water used by the crop. When properly managed, irrigation based on ETc minimizes crop stress caused by either insufficient or excessive soil water.

ETc is calculated by multiplying daily reference evapotranspiration (ETo) by a crop coefficient (Kc). The ETo represents the weather component and can be gathered from the Georgia Automated Environmental Monitoring Network. The Kc represents the crop water requirement and changes according to crop development stage. For Solanaceae crops, the values used for each stage are 0.6 for the initial stage, 1.05 for midseason, and 0.8 for the end season.

The initial-stage coefficient represents the seedling stage and the period from transplanting until root establishment, usually about two weeks. After root establishment, the crop enters the vegetative stage, crop water demand increases, and the initial coefficient gradually changes to the midseason coefficient. The midseason stage is the most critical period and is used from vegetative growth through flowering and fruiting. When plants begin to senesce, water uptake shifts more toward maintenance than reproduction, reducing water demand. At that point, the coefficient is reduced to the end-season value. For crops harvested multiple times, the end-season coefficient is recommended only for the final harvest.

Scheduling Irrigation Events for Solanaceae Crops in Georgia

Bell peppers, tomatoes, and eggplants are the main Solanaceae crops grown in Georgia. They are planted in March and April for the spring season and in August and September for the fall season. In both seasons, these crops are commonly grown under plastic mulch with drip irrigation, a system that allows growers to maximize irrigation water-use efficiency and crop yield by spoon-feeding water to plants.

The publication uses 18 years of historical information on ETc to develop weekly irrigation scheduling guidelines for four planting dates in the spring and four planting dates in the fall across southwest, southeast, northwest, and northeast Georgia. Daily ETc from 2000 through 2017 was calculated using average ETo values from weather stations across the state and the standard crop-coefficient values for Solanaceae crops.

Spring

In spring, Solanaceae crops require relatively low irrigation volumes early in the season because of cooler air temperatures and low crop demand. Around the fourth week after transplanting, plant leaf area increases rapidly, and the crop water requirement rises sharply as temperatures also increase. During this period, water stress should be avoided because both water deficits and excessive water can reduce yield and fruit quality.

For crops with multiple harvests, irrigation must continue through flowering and fruiting. High late-spring temperatures in Georgia can stress plants if water is not sufficient, so irrigation should only be reduced a few days before the final harvest as plants begin to senesce.

Week after planting	Southwest				Southeast				Northwest				Northeast
	3/1	3/15	4/1	4/15	3/1	3/15	4/1	4/15	3/1	3/15	4/1	4/15	3/1	3/15	4/1	4/15
	inches of water per week
1	0.33	0.42	0.48	0.60	0.30	0.38	0.44	0.56	0.25	0.33	0.39	0.50	0.26	0.34	0.40	0.52
2	0.41	0.50	0.57	0.66	0.38	0.44	0.52	0.60	0.33	0.40	0.47	0.57	0.33	0.39	0.48	0.55
3	0.42	0.48	0.60	0.71	0.38	0.44	0.56	0.65	0.33	0.39	0.50	0.60	0.34	0.40	0.52	0.60
4	0.88	0.99	1.16	1.27	0.77	0.91	1.04	1.16	0.69	0.82	1.01	1.05	0.68	0.84	0.95	1.06
5	0.85	1.05	1.24	1.41	0.77	0.97	1.13	1.33	0.69	0.88	1.04	1.20	0.70	0.91	1.05	1.22
6	0.99	1.16	1.27	1.37	0.91	1.04	1.16	1.22	0.82	1.01	1.05	1.16	0.84	0.95	1.06	1.14
7	1.05	1.24	1.41	1.47	0.97	1.13	1.33	1.33	0.88	1.04	1.20	1.28	0.91	1.05	1.22	1.27
8	1.16	1.27	1.37	1.46	1.04	1.16	1.22	1.32	1.01	1.16	1.27	1.32	0.95	1.06	1.14	1.28
9	1.24	1.41	1.47	1.42	1.13	1.33	1.33	1.32	1.04	1.20	1.28	1.32	1.05	1.22	1.27	1.30
10	1.27	1.37	1.46	1.52	1.16	1.22	1.32	1.43	1.05	1.16	1.27	1.40	1.06	1.14	1.28	1.43
11	1.08	1.12	1.08	1.17	1.01	1.01	1.00	1.07	0.91	0.98	1.00	1.09	0.93	0.97	0.99	1.08
12	1.04	1.11	1.16	1.20	0.93	1.01	1.09	0.99	0.88	0.97	1.07	1.01	0.87	0.97	1.09	1.05
Total	10.7	12.1	13.3	14.1	9.8	11.0	12.1	13.0	8.9	10.2	11.5	12.5	8.9	10.2	11.5	12.5

Fall

Unlike spring, irrigation requirements for Solanaceae crops are high early in the fall season because of high air temperatures, even though crop size and water demand are still relatively small. Since newly transplanted crops also have poorly developed root systems, irrigation events should be more frequent in order to reduce water stress and ensure plant survival.

As crops grow in the fall, water-use volumes peak because of rapid canopy closure. From four to eleven weeks after transplanting, declining air temperatures reduce irrigation volumes, but this does not mean crop water demand becomes unimportant. Water remains crucial during flowering, fruiting, and harvest to maintain fruit growth and quality. As in spring, irrigation should only be reduced a few days before the final harvest.

Week after planting	Southwest				Southeast				Northwest				Northeast
	8/1	8/15	9/1	9/15	8/1	8/15	9/1	9/15	8/1	8/15	9/1	9/15	8/1	8/15	9/1	9/15
	inches of water per week
1	0.75	0.74	0.65	0.60	0.70	0.68	0.59	0.55	0.21	0.20	0.18	0.16	0.19	0.19	0.16	0.15
2	0.75	0.71	0.63	0.53	0.70	0.64	0.57	0.49	0.21	0.20	0.17	0.15	0.19	0.18	0.16	0.14
3	0.74	0.65	0.60	0.51	0.68	0.59	0.55	0.46	0.20	0.18	0.16	0.14	0.19	0.16	0.15	0.13
4	1.24	1.10	0.93	0.79	1.11	1.00	0.86	0.69	0.34	0.30	0.26	0.22	0.31	0.28	0.24	0.19
5	1.13	1.04	0.88	0.71	1.03	0.95	0.81	0.64	0.31	0.29	0.24	0.20	0.28	0.26	0.22	0.18
6	1.10	0.93	0.79	0.69	1.00	0.86	0.69	0.63	0.30	0.26	0.22	0.19	0.28	0.24	0.19	0.17
7	1.04	0.88	0.71	0.57	0.95	0.81	0.64	0.53	0.29	0.24	0.20	0.16	0.26	0.22	0.18	0.15
8	0.93	0.79	0.69	0.63	0.86	0.69	0.63	0.47	0.26	0.22	0.19	0.14	0.24	0.19	0.17	0.13
9	0.88	0.71	0.57	0.43	0.81	0.64	0.53	0.39	0.24	0.20	0.16	0.12	0.22	0.18	0.15	0.11
10	0.79	0.69	0.53	0.36	0.69	0.63	0.47	0.32	0.22	0.19	0.14	0.10	0.19	0.17	0.13	0.09
11	0.54	0.43	0.33	0.23	0.49	0.40	0.29	0.20	0.15	0.12	0.09	0.06	0.13	0.11	0.08	0.06
12	0.52	0.40	0.27	0.20	0.48	0.35	0.25	0.18	0.14	0.11	0.08	0.05	0.13	0.10	0.07	0.05
Total	10.4	9.1	7.6	6.1	9.5	8.2	6.9	5.5	2.9	2.5	2.1	1.7	2.6	2.3	1.9	1.5

Food Safety Considerations

Because most Solanaceae crops are drip irrigated, the U.S. Food and Drug Administration’s Produce Safety Rule does not require irrigation-water testing in most situations, since the irrigation water is unlikely to contact the harvestable portion of the crop. However, the publication still recommends periodic microbial testing of irrigation water sources by collecting a 100 milliliter sample in a sterile bottle for generic Escherichia coli analysis.

Growers who choose to collect water samples may use the Produce Safety Rule guideline of 126 colony-forming units, or most probable number, per 100 milliliters as a reference point. Growers subject to third-party audits should consult their auditor for testing frequency and acceptable E. coli thresholds. Local UGA Extension offices can provide instructions for sample submission to the UGA Agricultural and Environmental Services Laboratories.

Summary

Weather variability, including temperature, solar radiation, relative humidity, and wind speed, is the main factor affecting ETc. As a result, irrigation requirements for Solanaceae crops in Georgia are generally more dependent on planting date than on location in the state. In spring, later planting dates require higher irrigation volumes than earlier planting dates. In fall, later planting dates require lower irrigation volumes than earlier planting dates.

The irrigation water requirements presented in the publication can be used for scheduling irrigation events, but even greater water-use efficiency can be achieved by combining ETc with soil moisture monitoring. Doing so helps ensure that irrigation never exceeds either crop demand or the soil’s field capacity. The efficiency of the irrigation system itself should also be considered before applying water.

References

Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). FAO Irrigation and drainage paper No. 56. Food and Agriculture Organization of the United Nations, 56, 97-156.

da Silva, A. L. B. R., Coolong, T., & Diaz-Perez, J. C. (2019). Principles of Irrigation and Scheduling for Vegetable Crops in Georgia (Publication No. B 1511). University of Georgia Extension. https://extension.uga.edu/publications/detail.html?number=b1511

Dukes, M. D., Simonne, E. H., Davis, W. E., Studstill, D. W., & Hochmuth, R. (2003). Effect of sensor-based high frequency irrigation on bell pepper yield and water use. In Proceedings of 2nd International Conference on Irrigation and Drainage (pp. 12-15).

Smittle, D. A., Dickens, W. L., & Stansell, J. R. (1994). Irrigation regimes affect yield and water use by bell pepper. Journal of the American Society for Horticultural Science, 119, 936-939.

U.S. Food and Drug Administration. (2015). Standards for the growing, harvesting, packing, and holding of produce for human consumption. Federal Register, 80, 74353-642.