Using Capacitance Probes to Schedule Furrow Irrigation on Cracking Clay Soils

Investigators: Himmy Lo, Jacob Rix, Drew Gholson, and Lyle Pringle

Date: 2022

Project Summary

Introduction

Using soil moisture sensors to schedule irrigation is a best practice promoted by the Row-Crop Irrigation Science Extension and Research (RISER) initiative at Mississippi State University. These sensors make it easier to give greater consideration to soil water reserves when making irrigation scheduling decisions. Over the past decade, Mississippi State University Extension Service has developed, validated, and disseminated guidelines on using the Irrometer Watermark 200SS sensor model (please see https://www.ncaar.msstate. edu/outreach/ for details). However, equivalent guidelines have not been established for other sensor models such as the Sentek Drill & Drop.

A major obstacle has been the difficulty of determining the threshold value for scheduling irrigation using the Drill & Drop. In other words, how dry can Drill & Drop readings become until drought stress starts to reduce crop yield? Existing data showed that this threshold value can differ widely across soil types and even among Drill & Drop installations within the same field. Thus, there is no universal threshold value, and there may not be a reliable way to predict the threshold value before installation.

As an alternative to focusing on the exact readings, both the manufacturer and other researchers have suggested scheduling irrigation by examining the daily drying rate of the Drill & Drop. However, past implementations of this method have depended heavily on the user's subjective interpretation. To tackle this limitation, NCAAR researchers have chosen to calculate a "relative drying rate" from the Drill & Drop and have been testing "relative drying rate" thresholds for scheduling furrow irrigation on cracking clay soils.

Materials and Methods

Four sensor-based irrigation scheduling treatments were each replicated on eight plots in a rectangular, precision-leveled field of the Sharkey soil series near Stoneville, MS. Pioneer P47A64X soybean was planted on April 29th at 140,000 seeds per acre in 40-inch twin rows and reached full maturity on September 22nd. Between the R2 and R6.5 growth stages, alternate-furrow irrigation was scheduled according to treatment-specific rules (Table 1). No irrigation was applied during other growth stages. Every irrigation application was cut off around the completion of furrow advance to minimize tailwater. From an area 20 feet wide by 500 feet long in the center of each plot, soybean yield was measured on September 27th using a Precision Planting YieldSense yield monitor with field-specific calibration by a weigh wagon.

Preliminary Findings and Next Steps

The Watermark 70-centibar treatment received the highest number of irrigation applications, received the highest amount of irrigation water, and produced the highest soybean yield (Table 2). On the opposite extreme, the Drill & Drop 50% treatment received the lowest number of irrigation applications, received the lowest amount of irrigation water, and produced the lowest soybean yield. Such a pattern of more irrigation leading to more yield was partially broken by the Drill & Drop 70% treatment. This exceptional treatment received almost two inches less irrigation but achieved statistically indistinguishable and numerically higher soybean yield when compared against the Watermark 100-centibar treatment. Further research is planned in preparation for creating proven guidelines on using Drill & Drop probes to schedule irrigation across the Lower Mississippi River Basin.

• Topic:
• Irrigation Scheduling
• Irrigation