In the summer of 2011, we developed an on-line Crop Water Use Calculator program which uses the Penman-Monteith equation. Preliminary field testing began in Missouri in our summer (northern hemisphere) and now we are testing it in South Africa (southern hemisphere summer). To make the program, we began with published crop coefficient curves for cotton, corn (maize), and soybean. For rice, Earl Vories (USDA-ARS) and Paul Counce from University of Arkansas developed an experimental coefficient curve for center pivot irrigation. Below is a screen grab from the Ukulima Farm weather page.
Note the new box in the center right side of the weather screen. Click on the Crop Water Use Calculator image. This will bring you to a new screen with options to select crop and planting date. As shown below, if you have a smart phone with internet access, you can do this in the field as you select the irrigation rate on a center pivot system.
One of the potential problems with growing rice with center pivots is deep ruts in the wheel tracks in the outside span where water rates are highest. For our pivot in South Africa, Lindsay designed the system with rubber tracks on the last span. The wider traction stops the rutting problem. To protect the rubber from sunlight and minimize dry rot, a local metal fabricator built metal “fenders” for us. Our rice experiment has different rates of water (treatments) applied in specific places in the field. The goal of the study is to determine the minimum water needed to produce high rice yields. Our center pivot is equipped with solenoids at each drop hose. This allows us to pulse the water and vary rates of water based on our treatments programmed in the pivot control box. The photo to the right show the farm crew doing maintenance work on the solenoids getting ready for this season. We will drill the rice for the experiment on Monday.
This morning we visited another researcher on the farm who is doing a project using oxen. His objective is to improve soil quality and help small farmers in Africa who can not afford pesticides for weed control.
The soils in this region have low water holding capacity because they are very sandy with less than a 1/10 percent organic matter. The picture on the left shows an “ox powered” planter retrofitted with coulters for no-till planting in heavy residue mulch. The oxen were recently vaccinated with a live pathogen which is a serious disease in the area.
The oxen temperatures are being checked each morning. They will be injected with antibiotics when their fever spikes.
To improve the organic matter in the sandy soil, black oats were planted to provide residue mulch. This will also help suppress weeds. When the oats began to flower, a roller was to run through the field to break the stalks and kill the plants without having to spray herbicides. The oxen will be used to plant the field in the next couple of weeks.
Working in Africa is helping me with in unexpected ways with my crop research in Missouri. At Portageville, I have a new project funded by Cotton Incorporated studying winter cover crops for improving soil quality. In my test, I am evaluating rye, wheat, crimson clover, Austrian winter peas, and tillage turnips.
Based on what I am seeing in Africa, I plan to try rolling the plants when they begin to bloom to kill them. But I will not use oxen. Hopefully the thick mulch will provide some help suppressing Roundup resistant pigweeds in cotton.
Next to the oats field on the South Africa farm is an old peach orchard which was in bad shape last year. The farm crew pruned the trees and added a drip irrigation system to water the trees. I was excited to see how well the trees are doing this year. Hopefully there were be fresh peaches available to eat later in the summer!
One of the challenges that we are having growing center pivot rice in South Africa is the lack of effective herbicides for weed control. We are working to find a program that will cause minimum crop injury to rice on low organic matter, sandy soils. This summer in the Missouri, we evaluated several chemicals that are not normally used for preemergence weed control in rice in the United States. At the University of Missouri-Rhodes Farm at Clarkton on sandy soils we applied two rates each of oxadiazon (Ronstar®), acetocholor (Warrant®), oxyfluorfen (Goal®) and atrazine. Herbicides were applied 10 days before planting, at planting, and 10 days after planting.
The least amount of crop injury occurred in treatments with oxadiazon applied at low rate 10 days before planting. Oxadiazon caused 30% stand reduction in rice plants when it was applied at planting. Rice in plots with acetocholor or oxyfluorfen either failed to emerge or was very stunted regardless of when it was applied.
In the United States, oxadiazon is only labeled for turf weed control and is sold at prices too high for rice farmers to economically use in their fields. But in some other rice producing countries it is labeled for rice and sells for a reasonable price to use in production fields. Acetocholor or oxyfluorfen would only be useful in center pivot rice production if rice varieties were planted with resistance to the chemicals.
Much of my time in the last three years has been spent working on ways to help farmers apply irrigation more efficiently. Our goal is to conserve both energy and water while producing high crop yields. Evapotranspiration is the sum of crop water use and soil evaporation. Plant scientists often call this “ET”, an abbreviation for evapotranspiration. To read more about ET see “The Use of Evapotranspiration Estimates as A Guide for Scheduling Irrigation in Missouri”. ET is calculated from the standardized Penman-Monteith equation and expressed in millimeters or inches of water. Many farmers adjust water rate each time they irrigate and have a fixed schedule (e.g. twice a week). Others keep the same irrigation rate and vary the length of time between irrigations.
How much water can crop roots take up between rainfalls or irrigations? This is affected by soil texture, rooting depth, and the type of crop. As soils become drier, roots are not able to pull as much of the remaining water from the films surrounding soil particles. Generally, fine soil particles hold water tighter than coarse particles. Soil water deficit is the difference between the amount of water that currently is in a soil and the amount needed to fill the root zone back up to full capacity (called field capacity). Recommended allowable soil water deficit is the minimum stored water needed to grow high yields on sandy and silt loam soils with and without compacted layers called “pans”. Example: A heavy rain storm completely soaks a silt loam field of corn that has a pan restricting roots. Over the next few days, the roots can take up 1.00 inch of water before showing stress that will hurt yields. .
If ET following the rain averaged 0.25 inch per day according to the weather station, the corn should grow about 4 days without needing irrigation (1.00 ÷ 0.25 = 4). Daily soil water in the rooting zone can be tracked from the beginning of the growing season until harvest. In places where irrigation water is limited, it pays to keep a balance sheet for soil water deficit to determine how much to irrigated. Water deficit balance sheets for irrigation are similar to a checkbook registry. Rainfall and irrigation amounts are added and crop water use is subtracted.
In May 2011, farmers along the Mississippi River experienced the worst flood since the 1930’s. The hardest hit in the upper Delta region were the Missouri farms in the Bird’s Point Floodway in Mississippi and New Madrid counties. The U.S. Corps of Engineers blew sections of the Missouri levee to relieve pressure on the Illinois side.
Many homes and farm buildings were destroyed. I am working with district extension agents, Anthony Ohmes and Sam Atwell, to access the short-term and long-term soil damage on the the farms. A combination of deposition and erosion occurred in the floodway. In a few places, the productivity of fields were improved by silt deposits after the floodwater receded. But in “blow-outs” near the levee breaches, thick layers of sand were deposited. To make matters worst, an endangered species tern bird nested on the sand and prevented farmers from starting the process of moving the massive amount of deep sand off of their fields. The most devastating erosion in the floodway occurred midway in an area called O’Bryan Ridge. Roads were washed out and deep gullies trenched out from the force of the raging river current. In the southern end of the floodway near New Madrid, found many exposed tree stumps in fields that they had never seen before. The current apparent cause sheet erosion removing the topsoil down to the traffic pan.
A simple method is needed to aid farmers with midseason N decisions in rice in the Mississippi River Delta region. Experiments were conducted from 2004 to 2006 at Glennonville and Portageville, Missouri to evaluate visual and digital image measurements at internode elongation for predicting rice yield response to midseason N applications.
Example images (left to right- low preflood N to high preflood N) collected at internode elongation with a digital camera from 80cm X 115cm areas in rice plots. Values in the lower right corner of photos were the proportion of green pixels in images counted with Sigma Scan software.
A yardstick was floated on floodwater between two center drill rows and the numbers visible were counted. Inch digits on the yardstick were approximately 2.0 mm tall. Standing between adjacent rows and leaning over the sampling rows, we counted the inch numbers showing on the yardstick (not hidden by rice leaves) out of 36 numbers possible. When a rice leaf obstructed the view of one digit in a two-digit number to the point that it the whole number was not recognized, we did not count that number. The person taking the measurements always kept both eyes open during the readings.
Conclusion. No yield response was produced from midseason N when fewer than 13 numbers were showing on a yardstick floating between drill rows or more than 64 % of the pixels in digital images of plots were green.