Coping with Chemical Processes in the Soil with MOET
On an early sunny morning, Dr. Cezar P. Mamaril, 76 stands on one of seven sorjan plots in his farm in Masaya, Bay, Laguna. He looks around to determine how his rice crop in the irrigated portion between the sorjan plots is performing. Next, he turns to the upland crops on the sorjan plots, which are elevated by at least half a meter higher than the irrigated lowland ricefield below them.
Dr. Mamaril was a scientist at the International Rice Research Institute (IRRI) in the sprawling campus of the University of the Philippines at Los Banos. Before he joined IRRI in 1972, he was a soil chemistry professor in the Department of Soils, UP College of Agriculture where he obtained his undergraduate degree in agriculture major in soil science in 1955.
Right after graduation he worked as an assistant instructor in that department, and it did not take long before he obtained the Master of Science in Soil Chemistry from the University of Wisconsin through a USAID-NEC scholarship in 1958, and the Doctor of Philosophy in Soil Science with specializations in soil chemistry and soil fertility from the Kansas State University in 1963.
It was in Indonesia where he got the idea of sorjan plots when he was assigned by IRRI in 1972 to 1986 to establish and manage the International Network on Soil Fertility and Fertilizer Efficiency for Rice (INSFER). When he bought a farm in 1986, he thought of developing it into a show window for organic farming, both on lowland rice and upland crops like vegetables (mungbean, patola, upo, ampalaya, eggplant), sweet and
glutinous corn, cassava, ginger, pineapple, and some fruit trees like Malabar chestnut.
Originally, his farm had no sorjan plots, but Dr. Mamaril found it necessary to establish them so that he can also produce various upland crops while he produces lowland rice. Thus, he had to establish sorjan plots enough for the upland crops of his choice.
The sorjan plots and irrigated portion of his farm represent two different ecosystems: aerobic or upland soils and anaerobic or flooded soils.
Part of the soil in the sorjan plots, about 25 cm, was taken from the lowland ricefield below them. Additional soil was brought in from outside sources to bring the elevation of the sorjan plots to at least 50 cm high.
He decided to cement the sides of the sorjan plots to eliminate possible erosion. Each sorjan plot is about 250 sq. m., enough for several crop species in a season that can not be raised under flooded condition.
DIFFERENT SOIL REACTIONS
Dr. Mamaril, also a senior consultant of the Philippine Rice Research Institute (PhilRice), points out that while lowland rice is produced in flooded or anaerobic soil, upland crops need aerobic soil for proper growth and development. This is because the chemical processes in flooded soils greatly differ from those in aerobic or upland soils. Thus, one has to understand these processes to fully attain benefits from them.
He explains that flooded and upland soils vary in the relative proportion of their components. Ideally, upland soil has considerable volume of pore spaces occupied by air, while flooded soil practically has no air space because most of the pore spaces are occupied by water.
The presence or absence of air (oxygen) in the pore spaces has important implications on the biochemical processes in the soil such as in the decomposition of organic materials and their mineralization or absorption by plants.
Differences in the physical properties of upland and lowland soils also influence the consequences of inputs or fertilizers applied in the soil. Thus, the strategies and approaches in applying inputs like fertilizer differ.
In lowland soils where oxygen is almost zero, the nitrogen absorbed by the plants is in the form of ammonium. If upland or oxidized soil is flooded, the soil is gradually devoid of oxygen and, hence, the availability of oxygen in the soil is reduced. When nitrogen fertilizer is applied in upland soil, nitrogen is converted into nitrate, the form of N that is absorbed by upland crops. What is not absorbed by the plants is further oxidized into nitrite and finally into nitrogen gas, which escapes into the atmosphere.
Lowland soils are generally dark because of poor drainage, reduced condition, and very slow oxidation, says Dr. Mamaril. Dark color also indicates high amount of organic matter. These soils have medium to heavy texture such as sandy clay loam, silty clay loam to clay loam. The structure is generally platy because of puddling, and has hardpan.
Likewise, lowland soils are generally poorly drained, puddled, and have shallow water table. The absence of stories and presence of bumds (small dikes) are noticeable. Those with a hardpan deeper than 25 cm are more fertile than those with less than 25 cm.
In contrast, the color of upland soils could be light or pale, dark, or yellow or
red, says Dr. Mamaril. Light or pale colors indicate coarse-textured and highly leached soils, while dark colors indicate high organic matter content. On the other hand, yellow and red colors are associated with fine-textured soils and indicate some degree of mixing of subsoil and topsoil.
Upland soils also have low pH. The pH remains low unless ameliorated with lime, which is why lime is not needed in lowland soils since they already have a pH higher than neutral which is pH 7.
Dr. Mamaril stresses that although all kinds of texture are found in upland soils, loam soils are the best. All soil structures, except platy, are also found in upland soils. Soil drainage is moderate to well-drained, and the soil surface is either flat or sloping. Hardpan seldom develops in upland soils unless highly mechanized with heavy machines.
PH AND NUTRIENT AVAILABILITY
The soil pH is oftentimes used to determine soil nutrient availability, Dr. Mamaril points out. While the pH in upland soils does not change drastically in a short time, pH in a flooded soil changes once it is flooded. In soils with low pH, the pH increases to about neutral (pH 7) within two weeks of submergence or flooding. In soils with high pH, on the other hand, the pH immediately goes down to almost pH 7 upon submergence.
“This suggests that availability of soil nutrients is affected by soil pH,” says Dr. Mamaril.
He explains that when nitrate fertilizer is applied in alkaline soils (> pH 7), the plants release negatively charged hydroxyl ions when they absorb nitrate. As a result, the pH around the root surface remains alkaline, preventing the absorption of phosphorus, which gets precipitated as tri-calcium phosphate on the soil surface. If ammonium nitrogen (like ammonium sulfate) is applied, the plants release hydrogen ions, which is good to them since those in lowland soils absorb ammonium (NHI) nitrogen.
Dr. Mamaril says the stabilization of the soil pH at neutrality after flooding has several effects on rice growth. For instance, the adverse effects of low or high pH are minimized. Excess aluminum and manganese in acid soils are rendered harmless. Iron and manganese toxicity in acid soils (below pH 7) is lessened, but the availability of phosphorus, molybdenum, and silicon is increased. Mineralization of soil organic nitrogen is favored, while organic acids are decomposed. Lime is seldom needed.
Excessive amount of iron in the soil is indicated by rusty spots on the leaves of plants, while a deficiency appears like nitrogen deficiency with more uniform yellowing on the leaves, he points out.
DEVELOPING THE MOET
Because of great differences in the chemical processes in flooded and upland soils, conventional analysis in soils laboratories either underestimate or overestimate the availability of soil nutrients, says this farmer-scientist.
He points out that the soil analyzed in any soils laboratory is dry and, hence, in oxidized condition. There’s a change in the state of some nutrients like nitrogen when the soil is flooded and, hence, the nutrients analyzed in oxidized form in the laboratory may no longer exist under flooded condition. Thus, nutrient status under flooded condition could be very different from the results of laboratory analysis.
For example, it may appear in a laboratory analysis that a soil has sufficient amount of sulfur and phosphorus. Under flooded condition, however, these soil nutrients may be deficient or excessive, thereby causing toxicity.
Moreover, besides being costly, many farmers do not have access to soils laboratories. Thus, it would be extremely difficult to assess soil fertility in places where this kind of laboratory does not exist.
These concerns “forced” Dr. Mamaril to develop an easy and cheap way of assessing soil fertility in ricefields in South Sulawesi, Indonesia in 19721980 where he was assigned by IRRI to establish the INSFER. Because of the absence of a laboratory with sophisticated equipments, he had to conduct pot experiments using four soil elements – nitrogen (N), phosphorus (P), potassium (K), and sulfur (S).
In one pot, he applied all the four elements while in each of the other four pots, he did not apply one of the four elements-minus N, minus P, minus K, or minus S. Each pot was planted to two seedlings and one of these was grown until maturity because most of the soil nutrients are important until maturity.
It was through this simple technique that sulfur deficiency was found widespread in Indonesia. He eventually named the technique minus one element technique or MOET when he joined PhilRice in 1997. He further refined it, adding zinc (Zn) and copper (Cu) to the original four elements, hence, the MOET now also determines the availability of N, P, K, S, Zn, and Cu in flooded soils.
The success or failure of a rice crop, barring unfavorable weather conditions, could be spelled by the availability or deficiency of any of these elements. “If zinc and sulfur are deficient during the early vegetative stage, the plants produce less tillers and even if the plants recover later, the damage has been done already,” says Dr. Mamaril.
The concept of the MOET is not new. “This concept has been known in soil science for a long time already, but nobody worked further on it,” he adds.
He was reminded about the concept when he started his work in Indonesia. “Instead of sitting down on a desk to figure out soil problems in the region, I was reminded of what I learned in soil science. So I set up pot experiments, using chemicals from pharmaceutical stores.”
“We found that not only NPK were deficient in Indonesian soils. We discovered that sulfur deficiency was so extensive such that even with the application of so much urea, the plants became more stunted.”
He also recalls that rice in Indonesia at that time was infected with tungro disease. Rice plants infected with the tungro virus become stunted and so the entomologist in his team said the stunting was caused by the disease. “You find green leafhoppers (GLH) in tungro-infested plants. Without the GLH you are assured that stunting is caused by sulfur deficiency,” Dr. Mamaril said.
He confides, however, that he did not report much on the new technique when he was still at IRRI, thinking that it was low-tech compared to what his fellow scientists were doing.
Moreover, the world renowned Filipino sociologist, Dr. Gelia T. Castillo, a member of the PhilRice Board of Trustees, reportedly asked Dr. Mamaril why he did not talk much about the MOET when he was still at IRRI. He replied that there was no pressure to release it.
FOR SMALL-SCALE FILIPINO FARMERS
When he retired from IRRI in 1996 and joined PhilRice as a senior consultant in 1997, he thought of further developing the concept for small Filipino farmers. He thought that with the use of the MOET, they would be able to diagnose nutrient deficiencies, thereby saving them from the trouble of locating the nearest soils laboratory and paying a high cost.
It was Josue Descalsota who did extensive testing of the MOET kit in the field when Dr. Mamaril retired. Today, MOET has been tested in many fields nationwide, and valuable data were gathered.
More and more farmers are saying that MOET may not be as sophisticated as other discoveries, but farmers can do it easily. Together with the LCC (leaf color chart), MOET will go a long way in the national effort of attaining rice self-sufficiency.