International Arid Lands Consortium

IALC Peace Fellowship Report
Summer 2000

Nancy Arruda
Undergraduate Student
University of Illinois at Urbana-Champaign

Comparative Studies of Soil Properties along a Rainfall Gradient
in the Negev

Through an IALC Peace Fellowship, I spent nine weeks studying laboratory methods and analysis at the Sde Boker campus of Ben Gurion University. I worked primarily with Dr. Eli Zaady on different projects centered around soil productivity, land use, and the prevention of desertification. Seeing how agriculture works in an arid environment was an eye-opening experience. By using runoff, wastewater, and conservation, scientists have found innovative ways to make plants grow.

 

Dr. Zaady's ongoing study concerned the effect of external factors such as grazing, herbicides, and scraping on soil crust. Soil crust is important to vegetation in the desert because it prevents runoff and conserves water. Because of the summer heat, there was no field work going on, and because of my short stay, I was not able to do my own research project. Instead, I learned a lot of different laboratory methods and a lot about the research process. This has been most valuable to me since I hope to go into research. Although I was not able to collect samples, I was taken into the field on several occasions so I could understand how the projects were created and the part I played in them.

 

I learned soil methods to test for chlorophyll, phosphorus, and polysaccharides. Summaries of these procedures are at the end of this report. These all involved chemistry that I was not completely familiar with when I started the work. I'd done similar tests in my lab classes, but never before had I the feeling that my results really meant something.

 

The chlorophyll was measured to determine the amount of soil crust present. In the desert landscape, it was evident that some areas were covered more densely with a greenish crust than other areas. Through Dr. Zaady's studies, this crust has shown to be important to preventing water runoff. An experiment was set up to determine what effects grazing, herbicide, and removal had on the recovery of the crust. The grazed area recovered the most quickly. The scraped area was starting to recover after several years. The sprayed area was still not recovering.

 

The polysaccharide test also tested for the amount of soil crust. The amount of glucose in the soil was measured to determine the amount of soil crust. This was similar to the chlorophyll test.

 

The phosphorus testing was done to determine soil fertility in Bruce Kahn's study. The experimental factors were grazed and non-grazed areas, as well as areas protected by shrubs versus those that were not. The areas where samples were collected were used by Bedouin to graze their sheep. The area was dotted with bushes that protected other plants from being grazed. Grazing was actually proving to be beneficial to the soil fertility.

 

I also assisted with Dr. Zaady's soil productivity study. We looked at the biomass and yield of wheat plants to determine the productivity of the land. The research area was outside Beer Sheva and had been unproductive the past two years because of drought. We analyzed the affect of rainfall gradient, land use, and runoff on the growth of the wheat. I was able to see this land as well as the origin of the soil samples, so I had a feeling for the applications of the research.

 

My learning extended beyond the lab work. Not only had I never left the US before, but I had never lived in a small town before. Sde Boker is in the heart of the Negev and I could walk its circumference in about twenty minutes. Because of this setting, I was able to get to know a lot of different people more closely than I would in a city. A course for international students was going on when I arrived, and my neighbors were from all over the world. I met not only Israelis but Kenyan, Kazakhstani, and South African students. We were from all over the world, but all had an interest in Israel and environmental research. I learned more about different parts of the world than I could have from books, and saw the benefits of cooperating on an international level to preserve land.

 

On weekends I was encouraged to travel around the country. Traveling within Israel was very easy and I took advantage of it. I saw the coral reefs in Eilat and floated in the Dead Sea. I learned about Israel's history through archaeological sites including Masada. I saw the amazing sites of Jerusalem, traveled to the beautiful Tel Dan Reserve in the north, and spent time in Haifa and Tiberias. It was amazing how diverse such a small country could be.

 

My time in Israel is something I will never forget. I was given the opportunity to learn about life in Israel, an ecosystem in a different climate, and the international research community. I learned so much through the funding of the IALC and the guidance of Dr. Zaady. I would encourage anyone with an interest in land preservation to become a Peace Fellow.

 

Summaries of Procedures:

 

Determination of Chlorophyll: This procedure was used to measure the amount of soil crust in the soil. Soil crust is important to preventing wind erosion and conserving water. A piece of soil crust 2cm by 2cm is cut and crushed into a test tube with Sml methanol and then cooled at 60 C for 2 minutes in a bottle sealed to prevent evaporation. The mixture is centrifuged for 10 minutes at 4000rpm. The liquid is transferred to a spectrophotometer tube and read at 665nm. Using a mathematical formula the weight of chlorophyll per square centimeter of soil surface is determined. The amount of soil crust from different areas can then be compared.

 

Polysaccharide test for soil crust: To 1 gram of soil, Sml of 3N H2S04 is added. The mixture is autoclaved for 20 minutes, vortexed, and then centrifuged at 4000rpm for 10 minutes. The mixture is filtered and built to Sml with H2S04 and mixed with 2ml reagent. The liquid is diluted and read at 620nm. The concentration used in the spectrophotometer has to be experimentally determined so the color changes can be measured against the standards.

 

Determination of Phosphorus: 5 grams of air dried soil are shaken for one hour to loosen the particles. The mixture is then centrifuged for 10 minutes and filtered. An experimentally determined amount of the liquid is added to the reagent and the resulting color is measured at 880 nn. These readings are compared to standards of known phosphorus concentration.

 

[edited for the Web by Elaine Cubbins]

 

 
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