Fertilizer : Managing Possible Nutrient Losses in Your Field
With the rising cost of synthetic fertilizers in the market, it is evident that many corn farmers started reducing their use of fertilizers on a per bag basis. For the first time, financers started cutting lending to growers because fertilizers are too expensive to be bundled with hybrid seeds and other farm inputs. And besides, even fertilizer dealers felt the crunch and they themselves have difficulty. Result: prominent pale green cornfields and some significant areas left idle for what used to be a vast lush cornfields.
In reaction, the government introduced newer and cheaper way of helping our corn farmers, seed inoculants and use of organic fertilizers. While it can be of help, educating our farmers on some basics in nutrient management remains integral. It is a known fact that majority of our farmers do not know anything about soil analysis and do not have access to such services. What they know for sure is that all plants need nutrients in the form of fertilizers, however, they are not aware of what 14-14-14 and 46-0-0 tells them. Well, of course they know the names - complete fertilizer and urea, respectively - but whether they know how much and when are these applied is another story.
REALITY CHECK
The adequate supply of plant nutrients is vital for efficient crop production in the humid tropics such as the Philippines. Soil in these areas are generally highly weathered and leached. A good nutrient management strategy, therefore, is to increase nutrient reserves in the soil and their availability to crops, and assess the requirement of the crop to be grown. But it’s a reality that Philippine soils grown to commercial corn are very low in nutrient reserves which then warrants the supply of nutrients from outside sources.
Before, we have tackled the value of nutrient management in attaining high yields. Likewise, we have touched on nutrient deficiency, how to recognize problems and correct them. In greater length, we’ll touch on the most expensive item in your list of inputs - inorganic fertilizers. We’ll write about how chemical fertilizers can be reduced drastically by decreasing possible losses, recycling nutrients, and through biological nitrogen fixation.
MOST COMMON TYPES OF FERTILIZERS
Probably the most popular commercial inorganic fertilizers are the following:
I observed that, corn farmers prefer complete fertilizer (14-14-14) for basal followed by ammonium phosphate. As side dress, urea is the most popular and the next is ammonium chloride. Complete fertilizers ammophos and urea, however, are the top 3 most expensive (nearly breaching P2,000/50-kg bag). Actually, all fertilizer grades have increased their prices following world record-high petrol prices. This means that each kilogram of fertilizers nowadays costs P40. It’s like the price of a liter of local diesel.
How NUTRIENTS ARE LOST
Soil erosion. The extent of nutrient loss caused by accelerated erosion can be very high especially in bare or idle crop lands. However, significant losses can also be expected among cropped plowtill systems of seedbed preparation. In
Type NPK Analysis (%)
Complete fertilizer 14-14-14
Ammonium phosphate (Ammophos) 16-20-0
Muriate of Potash 0-0-60
Basal grade 10-10-20
Ammonium di-phosphate 18-46-0
Ammonium chloride 25-0-0
Ammonium sulphate (Ammosul) 21-0-0
Urea 46-0-0
a study conducted in Africa, the use of mulch and no-till systems resulted in zero soil loss and practically no nutrient loss in eroded soils as compared to corn-corn and legume-corn plow-till system.
Below is a diagram showing erosion control measures based on engineering structures. It may seem too technical but it gives us an idea of how such measures reduce nutrient loss and provide a sustainable approach in crop production especially in the hilly lands.
Leaching. Just like soil erosion, leaching losses can be pretty high in the tropics. With seepage water, nutrients leaking out of the root zone can be substantial and may no longer be utilized by the crop. Nutrient loss by leaching can be minimized by soil, crop and fertilizer management techniques. The use of deep-rooted crops (as in corn after onions) to capture nutrients translocated to the subsoil is important in reducing leaching losses. Split applications and use of slow release formulations are the other options. Maintaining high levels of soil organic matter content is likewise an important strategy. It is then recommended that corn growers start using or maintain organic fertilizers in their fertilization programs.
Volatilization losses. The warm and moist conditions of the tropics may accentuate volatilisation loss of nitrogen held by soil and applied via fertilizers and even among organic amendments. Soil temperatures at 40°C-50°C at 1 cm depth of the soil may trigger volatilisation. To manage this, use of crop residue as mulch and no-till systems are useful techniques in regulating soil temperature and moisture. Among chemical and organic fertilizers, volatilisation losses can be minimized by incorporating them into the soil rather than just leaving it exposed on the soil surface.
Weed competition. With limited nutrients in the soil, weeds can cause further harm on corn. Weeds can temporarily immobilize nutrients by absorbing them (at a rate much faster than the main crop) although it still remains within the ecosystem. Proper weed control can be achieved through appropriate soil management techniques and application of herbicides. The current biotech wonder glyphosate-ready hybrids are an excellent example of how nutrients can be utilized optimally only by the corn plants.
BIOLOGICAL NITROGEN FIXATION (BNF)
Augmenting the nitrogen (N) supply through BNF is a very good option for poor farmers. The amount of N fixed by legumes can range from 20 to 200 kg/ha/year, depending on the species, soil type, climate, and agro-ecosystem. Among the common legumes that can be grown as cover crops to procure mulch and increase BNF are kalopogonium or mungo-mungo (Calopogonium mucunoides), Centrosema (Centrosema pubescens), stylo (Stylosanthes gracilis), kadyos or pigeonpea (Cajanus cajan), and mungbean (most common).
MANAGEMENT SUGGESTIONS
To summarize, the diagram below shows the best strategies for decreasing chemical fertilizer requirements.
Our current economic situation will definitely drive every farmer to avail or think of cost-saving technologies. But at the same time, it will be extremely important to check on our current practices and correct or improve them. The following are practical suggestions:
1. Have your soil tested or analysed. In this way, only deficient nutrients will be supplied and soil conditions can be optimized if pH is outside the ideal range for corn (pH 5.5-7)
2. Add organic fertilizers in your fertilization program. It may not readily provide nutrients but several studies have shown good results if combined with commercial inorganic fertilizers.
3. If your crop land is hilly and prone to erosion, try conservation or no-till methods when planting corn. Glyphosate-ready and stack-trait hybrids are best fit in this system.
4. When applying fertilizers, make sure there is enough soil moisture. It is best to follow basal and side dressed fertilizers with irrigation, if available. Often times, basal fertilizers are not covered with soil because the common practice of manual application Hilling-up to incorporate urea into the soil is a standard practice to prevent nutrient loss into the atmosphere (under dry, hot weather).
Frequently Asked Questions:
To save on labor cost, some farmers apply fertilizers one time. Is this correct?
No. It is highly recommended that growers apply basal fertilizers before or during planting and another one after 25 to 30 days after plantings as side dress. All phosphorus (P) and potassium (K) are recommended to be applied in the seedling stages to assist in root and stalk development whereas half of the recommended N is enough to support vegetative growth. The remaining half of the required N will be needed in the later stages to support flowering and seed set. In short, some nutrients are required early in the life of plant and some in the more mature stages. Split applications can likewise ensure that fertilizers are applied and absorbed properly without the risk of leaching and volatilisation. Delay or improper timing in the provision of important nutrients will have significant impact on the crop’s performance and this is not economically beneficial.
