Irrigation and Nutrient Management to Maximize Vegetable Yield and Minimize Pollution

View the project final report

Commodities

• Vegetables: beans, broccoli, cabbages, carrots, cauliflower, eggplant, peppers, cucurbits, tomatoes

Practices

• Crop Production: irrigation, nutrient cycling, organic fertilizers, tissue analysis
• Education and Training: decision support system
• Farm Business Management: whole farm planning, budgets/cost and returns
• Production Systems: organic agriculture
• Soil Management: soil analysis, nutrient mineralization, soil physics, soil quality/health

Locally grown food initiatives are allowing intensive agriculture to return to the Blackstone River Valley and with it come the associated challenges of nitrate (N) leaching and phosphorus (P) runoff. Agricultural N and P losses reduce soil fertility, are expensive, and pollute surface and ground waters. Community Harvest Project, a non-profit, volunteer farming organization located in North Grafton, MA wants to maximize vegetable yield and quality while minimizing any harmful environmental consequences. This project seeks to increase water and nutrient use efficiency by setting up an automated measurement and control module to trigger irrigation & fertilization; and to make this information available "real time" through the internet. The technology applied and information available will establish the Brigham Hill Community Farm as a model of sustainable agriculture in the region; conserve the Blackstone Valley's natural resources and historic land use patterns; and ameliorate river health. CHP's focus on the educational aspects of the project & establishment of a WIKI will promote awareness & stewardship, and allow for widespread dissemination among partner agencies.

Locally grown food initiatives are allowing intensive agriculture to return to the Blackstone River Valley and with it come the associated challenges of nitrate (N) leaching and phosphorus (P) runoff. Agricultural N and P losses reduce soil fertility, are expensive, and cause eutrophication of surface waters. Combined with other sources of nutrients (i.e., from septics and lawns) surface waters become overgrown with aquatic vegetation that dies in the winter. In the spring, the dead plant material and dissolved oxygen is consumed by biological decomposition. Without oxygen, the fish can‘t breathe and leave the area or die.

Lake Ripple in Grafton, MA provides a venue for hikers and anglers. It is bounded on the west by Potter Hill and Brigham Hill. On top of both hills are farms; one owned by Community Harvest Project (CHP) and the other by the Grafton Land Trust. Both organizations desire preservation of farmland and water resources in Grafton, near the headwaters of the Blackstone River Valley at the confluence of the Quinsigamond and Blackstone Rivers.

Extended dry periods and well drained soils require use of irrigation for vegetable production in the Blackstone River Valley. Many growers already supplement rain with drip irrigation, a low water volume style of irrigation. With this technology, soil moisture can be maintained at the optimum level for maximum crop production. The question remains, what is the optimal irrigation schedule to maximize productivity while allowing the most soil water storage capacity to capture impending rain without leaching nitrate N.

The question regarding the optimal frequency and duration of drip irrigated row crops to reduce nitrate leaching was investigated by Waddell et al. (1999 and 2000). In that experiment, I automated an irrigation system using tensiometers. Tensiometers measure the soil-water tension, a direct measure of the force required by plants to extract water from the soil. Replacing the gauge with a digital pressure transducer allows electronic signaling and control of irrigation. If the tension on the tensiometer becomes too large, air will enter the device and the gauge will read zero; the tensiometer is said to have broken. If the soil dries enough to cause the device to break, crop yield and quality were already significantly impacted.

Tensiometers have an advantage over other types of soil moisture sensors because they work in the wet soil range and work independently of soil type or density. If growers think they are irrigating properly based on sight or feel, they most likely either over-irrigate, wasting water and money or they under-irrigate impacting yield and quality. Several authors have suggested various triggers for initiating irrigation. I proposed a soil water potential trigger of 30 kPa (4.3 psi) to initiate irrigation when threatened with summer thunderstorms. Shock et al. (2005), proposed 20 kPa for onions in a semiarid climate with one drip line for two rows of plants unthreatened by frequent summer thunderstorms Both worked well for the various situations—but the 30kPa trigger maximized yields while also limiting nitrate leaching by efficient use of water and nutrients.

Once irrigation is initiated, the next question is to determine the proper duration of the irrigation event. With the flow rate of 0.45 gallons/minute/100 feet, drip tape can provide 0.14 inches of water per hour when spread evenly over the soil surface. Crop demands may exceed ¼ inch per day and soil water storage is adequate for about 3 days on a sandy loam (Waddell et al., 1999).

Proposed are two strategies of drip irrigation:
- To maintain ideal moisture content in wetted soil portion by pulsing irrigation every three hours for 30 minutes based on tensiometer data, or
- To attempt to refill the soil to field capacity with irrigation events lasting 2 hours when needed daily.

This project proposes to evaluate the High Frequency/Low Duration irrigation management strategy versus the Low Frequency/High Duration strategy on yield, quality, water, and nutrient use efficiencies.