Soil moisture and rice roots


One of the fun parts of working at Ukulima Farm in South Africa is the exchange of ideas between the research partners. Claire Lorts and Larry York, PhD grad students from the Penn State University Root Lab, went the extra mile and offered to sample and examine rice roots from our small plot rice variety test. Their advisers are Kathleen Brown and Jonathan Lynch. Information about the PSU root lab can be found at Shown with me, left to right, collecting root core samples in the rice plots are students Jacob Mtladi, Rodney Managa, Claire Lorts (holding hammer), and Tsitso Mokoena.  .

Sprinkler irrigation was applied during the season based on ET calculations except in early January when a supply line broke between the pump at the river and the center pivot.  Several days were required to find the location of the break and fix the pipe. During that time (Jan 2 to 14), soil moisture in the 0 to 20 cm depth became very dry causing many small tillers to turn brown and die on the rice plants.

Although this was unfortunate for the overall rice yields, it gave us an unexpected opportunity to see which rice varieties had the least damage from water stress. The variety showing the least visual above ground plant stress was Cardi 70-3 from Cambodia.

The Penn State root scientists  used a technique called “shovelomics”  which is the act of digging up roots and phenotyping them. Shown below are root balls from healthy rice plant (top) compared to a plant variety that showed severe vegetative water stress (bottom).

Also, evaluated by the root biologists was the angle of the roots.  Generally, plants with roots growing in a downward angle extract soil water deeper and withstand short term periods without water better than plants with shallow roots.




Below are preliminary results from the plant and root measurements and rice grain yields in the small plot variety test.  Rice is normally flood irrigation. These lines were identified from aerobic screening research in Texas and Missouri as possibly being able to withstand water stress better than other rice varieties.  Values for tillers and roots are numbers per plant.

  • Rice variety            # tillers       #roots    yield, bu/acre
  • Best 2000                   8.0          133          12
  • Cirad 141                   9.8           187          15
  • Nerica 6                      6.0          181           33
  • Zhe 733                       9.3         196            20
  • Wells/Nerica 4           10.5         175           53
  • IAC 201                      9.3           160           30
  • Cardi 70-3                  6.0           117           79
  • Nerica 4                     9.8           189           52

We observed “hollow” areas in the center of root balls that were caused either by a “die off” of roots in  due to water stress in early January or that some rice varieties just naturally stop growing new roots in the parent plant in the center when tillering begins.  The root diameter measurements are still being processed.

Cardi 70-3 had the least number of tillers and roots per plant, but produced the highest grain yield.  This is the opposite of what one might expect. Perhaps this variety partitioned more energy into growing fewer but larger roots to grow deeper in the soil. Shown below are photos of Larry York and Dominik Mtladi scanning rice roots to evaluate diameter and branching.