Some notes on the soils in the vegetable landscape of Benguet, Northern Luzon

Soils are formed from the weathering of rocks as influenced by climate, parent rock, topography, living organisms, and time. Among these factors, climate and topography appear to be the dominant factors that have influenced the properties and distribution of soils in Benguet, Northern Luzon. 

Benguet together with Abra, Apayao, Baguio City, Ifugao, Kalinga, and Mountain Province comprise the Cordillera Administrative Region (CAR). Benguet has a mountainous topography consisting of peaks, ridges, and canyons ranging in elevation from about 900m to 2,840m above sea level. 

The highest point of the Philippine highway in Cattubo, Atok, Beneguet

The subtropical highland climate (Cwb based on Köppen climate classification) with annual average highs of 25.3 °C in April and lows of 13.3 °C in January and an average precipitation of 1,829mm (Wikipedia) promotes moderate rock weathering and soil formation rates. The steep slopes on most mountain sides enhances rapid leaching and runoff, the latter results in severe soil erosion on cultivated and bare slopes. 

Steep slopes with young soils are terraced and planted to various vegetables

Most soils in Benguet have developed from diorite, an intermediate plutonic rock, as well as metavolcanics and metasedimentary rocks particularly slate. According to the published literature, the dominant natural vegetation of Benguet was the pine forest type. Compared with broadleaf forests, pine forests have lower soil organic carbon (SOC) contents, smaller labile carbon fractions, and lower amounts of SOC stocks. Moreover, pine forests tend to experience severe water erosion events (Nie et al., 2019. Catena 174: 104-111).

Outcrops of metasedimentary rocks in Atok, Benguet

The high soil erosion rates result in poorly developed and thin soils (Inceptisols). On more stable surfaces such as on summit positions, old soils can be found which may qualify as Ultisols. Regardless of the stage of soil development, most soils are acidic with pH below 5.0 (Laurean et al., 2015. Benguet State University Research Journal 74: 10-34).

Red and old soils on summit positions in the mountains.

Where intensive vegetable production is found, the landscape can be called Anthropocene landscapes due to the considerable soil and landscape modification resulting from human activities such as land use conversion from forest to agriculture, terracing, fertilizer and pesticide application, liming and others.

The beautiful Anthropocene vegetable landscape in Natubling, Buguias, Benguet.

In general, the rates of fertilizer and lime application by the vegetable farmers are not based on recommended rates. This necessitates soil fertility assessment of vegetable farms to be able to determine the appropriate rates of fertilizer and lime application for improved vegetable production. This is one of the objectives of our ACIAR SlAM Project (2020117) on managing heavy metals and soil contaminants in vegetable production led by Dr. Steve Harper of the University of Queensland, Australia.

Our ACIAR Slam Project Team from the Univ Queensland, UPLB, BSU, VSU & USTP

Impact of intensive vegetable production on the organic matter, nitrogen, and phosphorus levels of a volcanic soil (Andisol)

by Niezel Jane D. Estrellanes

Volcanic soils such as Andisols have many unique properties not usually found in soils derived from other parent materials (http:/www.ctahr.hawaii.edu). They are often very young and acidic depending on which type of volcanic materials they come from. They also largely consist of non-crystalline minerals such as allophane and imogolite (Nanzyo et al., 2002) which form strong bonds with organic matter thereby protecting it from decomposition. Andisols are usually light textured and are easy to till. However, they form strong complexes with phosphorus, rendering this element unavailable to plants.

One of the sampling sites in the central volcanic highlands of Ormoc, Philippines

This thesis research, a component of the Australian Center for International Agricultural Research (ACIAR) Soil Project based at the Visayas State University, evaluated the impact of intensive vegetable production on the nitrogen and phosphorus levels of volcanic soils in the central highlands of Leyte specifically in Cabintan, Ormoc City, Philippines. Twelve sampling sites (vegetable farms) including a reference site were chosen for this study. The objective was to find out if the continuous and heavy application of fertilizers for intensive vegetable production have caused the accumulation of nitrogen and phosphorous in Andisols.

Location of the sampling sites in Cabintan, Ormoc City

Soil samples were taken from the following soil depths 0-20, 20-40, 40-60, 60-80, and 80-100 cm using a soil auger. They were air-dried and passed through 2-mm sieve and analyzed for selected physical and chemical parameters such as pH (H2O, KCl, and NaF), available phosphorus, and particle size distribution. Enough 2-mm samples were also ground further and allowed to pass through 0.425-mm for organic matter content and total N analysis. 

Soil OM contents of the sampling sites. Sites 2, 4, 6 and 7 have much 
higher values than the reference site 12.

Soil N contents of the sampling sites. Most of the sites have much higher 
N levels than the reference site 12

Soil available P contents of the sampling sites. Reference site (12) has 
much lower P levels compared to all other sites.

Results revealed that the majority of the vegetable farms sampled showed higher amounts of organic matter (OM), nitrogen (N), and available phosphorus (P) than the reference site (secondary growth forest). This clearly indicates the impact of the high and continuous application of chemical and organic fertilizers (chicken manure). The very high nitrogen contents of the soils point out to nitrogen pollution which could have a serious negative impact on the groundwater quality. The high available phosphorus contents of the soils suggest improvement of the supply of this nutrient to the crops considering the fact that it is the major limiting nutrient to crop production in Andisols.

Based on the results it can be concluded that:

a. The intensive vegetable production has increased the nutrient status of the Andisol; 

b. The frequent and high rates of fertilizer application for the intensive vegetable production have greatly increased the nitrogen and phosphorus contents of the Andisol soil.

c. Nitrate and phosphate pollution of the groundwater and the nearby rivers may result from intensive vegetable production. 

Some notes on the soils and use of fertilizers and pesticides by vegetable farmers in Claveria, Misamis Oriental, Philippines

The gently rolling topography which typifies a large portion of the volcanic landscape in Claveria makes it ideal for intensive large-scale vegetable production. The widely grown vegetables include cabbage, beans, tomato, sweet pepper and eggplant.

The breathtaking volcanic landscape of Claveria, Misamis Oriental

But the strongly weathered soils which range from Oxisols in the lower slopes (about 400 to 600 m above sea level or asl) to Ultisols in the upper slopes (about 600 to 900m asl) are a major constraint to vegetable production in the area. Oxisols (also called Ferralsols) and Ultisols (also called Alisols and Acrisols) are clayey, reddish, acidic and nutrient-poor soils although they generally have good physical properties like good structure and moderate to high porosity. As in other volcanic landscapes, the oldest and most infertile soils (Oxisols) are formed on the older and stable lower slopes.

Dr. Apol & Nelds Gonzaga, Ruby Gabaca, Dr. Steve Harper & myself in front of an Ultisol soil at 920m asl. 

Farmers are apparently aware of the chemical and nutrient limitations inherent in these soils. That is why they apply lime and a variety of chemical and organic fertilizers. Rates of application are, however, not based on soil/plant tissue analysis but on what the farmers perceive as necessary. Thus, the rates appear to be insufficient in the case of lime, but excessive for the chemical fertilizers. This undoubtedly increases the production cost and can lead to more soil and environmental problems like acidification and groundwater pollution, respectively.

Heavy fertilizer application is done starting at planting of vegetables

Pest and diseases are also greatly affecting vegetable production in the Claveria landscape. As a result, farmers practice excessive application of pesticides which poses a serious threat to the health of the farming families, the consumers in urban centers, and the environment in general. The lack of awareness among farmers about the proper application of pesticides can be seen from their improper handling of these hazardous chemicals and from the fact that they just leave the pesticide containers at the farm borders.

It is common for farmers to mix two pesticides with water and spray the cocktail to the vegetables twice a week

The above observations strongly justify the urgent need for research on soil and nutrient management as well as integrated pest management in Claveria.

Potassium availability in soils

Potassium (K) is second to nitrogen in terms of the amount absorbed by higher plants. Optimum K level for plant growth ranges from 2 to 5% of plant dry weight (Marschner, 1995). Unlike P, K is present in relatively large quantities in soils coming from the weathering of primary minerals such as feldspars, mica, and others. But it is commonly deficient in highly weathered or old soils. Total K contents of soils range between 3000 and 100,000 kg/ha in the upper 20 cm of the soil profile (Sparks, 2000). The behavior of K in the soil is influenced primarily by CEC and mineral weathering and not by biological processes.

Interrelationship of various forms of soil K (modified from Sparks, 2000)

K in the soil occurs in 4 forms: solution K, exchangeable K, nonexchangeable K, and mineral K (Sparks, 2000).

a) Solution K. This is the K dissolved in the soil solution. It is the form of K that is readily available to plants and soil microorganisms and also is the form of K most subject to leaching losses. It varies in amount from 2 to 5 mg/liter K but can be dramatically changed by the addition of k fertilizers to the soil.

b) Exchangeable K. This is the form of soil K that is adsorbed on the surfaces of soil colloids. It is readily exchanged with other cations in the soil solution and is also readily available to plants. Some authors combine exchangeable K and solution K into one form called readily available form of K which comprises only 1 to 2 percent of soil K. This is also dependent on the CEC of the soil.

c) Nonexchangeable K. This is the portion of soil K that is fixed or held between adjacent layers of 2:1 clay minerals particularly vermiculite and smectite clay minerals. This is continually released to the exchangeable form when levels of exchangeable and soil solution K drops due to plant uptake and leaching losses.

d) Mineral K. This is the K that is part of the crystal structure of primary minerals such as muscovite, biotite, and feldspars. It is the most abundant and accounts for 90 to 98 percent of soil K. It is unavailable to plants and can only be released to the soil solution upon weathering of the minerals.

Leaching is the major cause of loss of K in the soil. Leaching of soil solution K is greatly dependent on the CEC of the soil and thus is influenced by the amount and type of clay and the SOM content of the soil. Soils with higher CEC like clayey soils have greater ability to hold K and thus have lower leaching losses than sandy soils with low CEC. Excess application of K-fertilizers can also enhance leaching losses especially under conditions of high rainfall.

Another form of leaching loss of K (and other nutrients) which is often overlooked is the one that occurs from the leaves of the plants. This can cause substantial nutrient loss exceeding seven times the amount in the standing crop in the case of K. Nutrients are leached from the leaves in the order K>N>P although this would also depend on the nutrient status and leaf morphology. Anything that reduces the water contact with leaves like smooth cuticle, erect leaves, etc. also reduces leaching losses (Chapin, 1980).

References
Chapin, F.S. III., 1980. The mineral nutrition of wild plants. Ann. Rev. Ecol. Syst. 11:233-260.
Marschner, H. 1995. Mineral Nutrition of Higher Plants. 2nd ed., Academic Press, London.
Sparks, D.L. 2000. Bioavailability of soil potassium. In:  In: Handbook of soil Science (M.E. Sumner, ed.). CRC Press, Boca Raton, pp: D38-D53.

Challenges and opportunities in agriculture

by Dr. Cezar P. Mamaril
Senior Consulting Expert of Philippine Rice Research Institute (PhilRice)

Los Baños, Laguna

I would like to share my thoughts about current challenges and opportunities in agriculture that institutions like Visayas State University (VSU) should be concerned. I could not over emphasize the fact that we are facing the problem of producing sufficient food to feed the ever increasing population of our country. Last census reported that our population is increasing by 2.3 percent, while our food production (particularly rice) is increasing by about 2.5 percent. The minimal growth difference between population and food production is not sufficient to provide the other requirements of small farmers to live a decent life. I hope the current census will show a decline in population growth so that we will have a better breathing space. (If you have not yet been interviewed by the census takers, you better do so otherwise you may not get your ration of rice!). Furthermore, some recent reports show that the per capita rice consumption in the Philippines has been increasing from less than 100 kg/year several years ago to almost 120 kg/year currently which suggest that some people can not afford to purchase other kinds of food besides rice. Yet in developed countries like Japan and Korea, the per capita consumption is decreasing with increasing income. I was told by my younger son who is an Agric. Economist that the Philippines is now the largest rice importer in the world. I read in the newspaper that this year alone, the government will be importing 2.45 million tons of rice. Is this a sign that Filipinos are retrogressing economically while our Asian neighbors are moving forward?

Besides inadequate food production, lands suitable for the expansion of food production is declining fast suggesting that time will come when we can no longer increase food production by expansion of area. Likewise, there is also the problem of conversion of agricultural lands for other human activities such as real estate housing projects, industrial activities, game parks like golf courses, etc. It is also unfortunate that most of these areas being converted into other human activities are productive lands mostly irrigated lowland rice areas. Since land is a finite resource, we should properly and efficiently utilize it.

Population also creates pressure on water resources which is quite critical especially in rice growing areas. Forests are also subjected to tremendous pressure with increasing population because of the demand for building materials and for fuel. With increasing deforestation, water resources will also diminish. Likewise, when water resources decrease, the share for agriculture for water will also decrease while domestic and urban needs increase because of increasing population. Thus, food production will be greatly affected especially for lowland rice and could lead to lower yields. It has been observed that not only the surface water resources that is affected by deforestation but also the ground water level. It is doubly serious especially in coastal areas because as the fresh ground water table gets deeper, sea water intrusion takes place to replenish the fresh ground water. Subsequently when ground water which is contaminated with sea water is pumped for irrigation the soil may become saline which is adverse to crops production.

The challenge therefore is how one can proceed to produce sufficient food for an unabated population growth with less land and declining soil productivity and less water resources and climate change. The current scenario looks bleak but we should remain optimistic and be challenged and remain hopeful for Divine intervention. We should put our efforts and minds together to use effectively and efficiently whatever resources are available.

Currently there are technologies being disseminated which are not cost effective because they are highly generalized rather than site specific. Thus most often farmers do not realize the benefits that are claimed to be obtained through these technologies. You may also agree with me that there is no “perfect” or “universal” technology that is appropriate for all sites and conditions. Technologies being generated should define the site characteristics and conditions where such technology is effective. Certain technologies are being disseminated prematurely; i.e. not extensively tested before being released for dissemination under all conditions and crops. What is effective for one crop is not necessarily true for all crops. A more specific example is technologies suitable for upland rice is not necessarily appropriate for irrigated or rainfed lowland rice and yet they are the same crop. A friendly advice to researchers is to define and characterize your experimental sites thoroughly so when you finally will disseminate your findings, you can specify where such technology works or where it does not.

In preparing research programs, it might be wise to involve the different stakeholders, such as the farmers and providers of farm inputs, to insure that there is relevance to the stakeholders’ need and capability and for the eventual adoption of whatever results generated by research. As researchers we often feel that we have better ideas than the farmers to resolve their problems and yet while research results might seem encouraging, farmers are hesitant to adopt these due to other factors that the research failed to consider during the process of conducting the study. I can cite several examples. A technology may produce successfully high yields but it requires high cost of inputs, both materials and manpower, which some farmers does not have the capacity to obtain the inputs. Naturally it is likely that many farmers will not adopt such technology. It might be a good idea to generate a cafeteria of technologies that require different levels of inputs and capabilities from which farmers can choose depending on their financial and technical capacities. Thus, socio-economic characterization of target stakeholders is imperative besides biophysicochemical characterization of the target areas.

There are rice areas where once farmers can grow two seasons of rice a year with reasonable yield but because of declining supply of water resources, the dry season rice crop often fails. Under such situation, crop diversification may be considered wherein during the dry season other crops should be planted. In choosing the alternative crop, however, the crop being introduced should have an economic value equal or better than rice if possible. Crop diversification will also enhance soil productivity. In a rolling landscape, it is possible that the bottom portion of the toposequence will be planted to rice while those in the top and slope portion to upland crops. Integrated crop diversification will likewise reduce economic risks on the part of the farmer.

With increasing cost of farm inputs, we should assist the farmers to utilize these external inputs effectively and efficiently as well as the proper utilization of farm biomass. One reason why chemical fertilizers are claimed to cause soil degradation is because of misuse rather than overuse of fertilizers which could lead to nutrient imbalance. There is increasing evidence of widespread multi nutrient deficiencies in our country especially in areas where crops are constantly applied with chemical fertilizers like rice, corn and sugarcane. This is because most often than not, only NPK fertilizers are applied and in the meantime the native supply of the other essential nutrients are being depleted. It is imperative that proper diagnosis of the nutrient status of soils should be regularly undertaken so that only the limiting nutrient should be applied in proper proportion to the other essential nutrients. Unfortunately the cost of soil analysis is beyond the reach of small farmers plus the fact that there are limited and inaccessible soil laboratories in the country. Therefore, there is a need to develop cheap and simple techniques to diagnose nutrient status of soils. Currently, the available simple diagnostic tools being promoted are the Soil Test Kit (STK), Nutrient Manager, a computer assisted method developed by IRRI, and the Minus One Element Technique (MOET) kit which is designed primarily for lowland rice soils.

Integrated nutrient management strategy may also reduce the cost of external input use especially if one will fully and efficiently utilized farm produced biomass as supplemental source of nutrients. Utilization of on farm biomass should not require special handling of the materials to the extent that additional time and facilities are required for the farmer to process these materials before such can be applied to the soil. Farmers usually are apprehensive to do extra efforts especially if the additional benefit will not significantly compensate the extra effort spent. More efficient and effective ways to utilize these on farm biomass has to be developed rather than the traditional composting and inoculating with decomposing or mineralizing organisms. There should be some means to stimulate the indigenous and heterogeneous soil organisms to decompose and mineralize organic materials rather than utilizing isolated pure strains of organism which will be an added cost to the farmer.

There must be many more opportunities that could enhance agricultural production and help uplift the well being of farmers but I leave them for you to think about. I would like to point out, however that based from my own farm experience, increasing production does not necessarily lead to better livelihood for a small farmer mainly because under our present situation, the middlemen or traders usually earn more than the farmers. Marketing is an important problem that small farmers face. Unless small farmers are organized to be able to dictate the price of their produce, they will never improve their lot. Unfortunately farmers’ cooperative movements in our country do not have a commendable history. These should be one area of interest that the new government should look into. Coincidentally, while preparing my talk, I heard in the radio last Wednesday, that one of the advocacies that the new Secretary of Agriculture Alcala has proposed to President Aquino during his interview for the DA position which impressed the President is the elimination of middlemen by providing opportunities for small farmers to sell their produce directly to the consumers. It will be interesting to see what plans, programs and strategies our new government will pursue to enhanced the well being of our small farmers and fisher folks.

In closing I would like to reiterate that we should remain optimistic that the seemingly bleak scenario of our agricultural sector mentioned earlier can be overcome if we put our acts together and with the guidance of our Almighty God. Moreover, I would like to leave the following quotation from Henry David Thoreau “If one advances confidently in the direction of his dreams, and endeavors to live the life which he has imagined, he will meet a success unexpected in common hours.” Success in any endeavor could be attained through perseverance, determination and hard work.

----------------
*Excerpt of keynote speech delivered during the College of Agriculture Day, Visayas State University, Baybay, Leyte on July 2, 2010.

*Dr. Mamaril is a retired UP Los Banos soil science professor and International Rice Research Institute (IRRI) scientist. He is the son of Mr. Julian Mamaril, the first Superintendent of Visayas Agricultural College (forerunner of Visayas State University) in the early 1960s.