Field aeration is important for the success of a crop. This can be achieved by working the soil with a plough (which ploughs to a 40 cm depth) or by planting a cover crop that aerates through its root system such as alfalfa (which has a root system 4-5 m deep.) Compaction of the soil is a major problem when seeding, chemical applications and harvesting is done by heavy duty machinery. Loosening up the soil improves the water distribution, breaks up mineral build-ups that create impermeable layers in the soil and improves the effectiveness of chemical applications.
The focus of today's lesson was the soybean. We've been working with the agricultural division which consists of Santiago, Mariano, and Mauricio. Planting depends on the commodity price of the soybean in the year of planting. Since the Argentinian government is not stable and there is not a strong local economy for the soybean, prices depend on the world market.
The soybean is planted in two seasons referred to as the first harvest and second harvest soy. First harvest seedings vary from year to year and are dependent on the climate and soil conditions of different plots at the time of seeding. Different varieties are used to respond to different conditions. Changes in seed result in different time requirements for germination and maturation.
The critical period for first harvest soybeans is the flowering stage. The soy plant is strongest when it has ample water access. When it experiences dry or drought conditions, the plant will abort flowers and thereby lose seedpods. Studying the rainfall patterns for the last thirty years at La Calanderia, it is known that December 15 - January 15 is a high temperature dry season. So the soy plants are planted so that the flowering date ( +/- 15 days) for the specific variety being used doesn't fall within this window of time.
For similar purposes, the second harvest soybeans are planted in December so that their flowering period occurs in February.
It is also important to recognize that short cylce plants are generally smaller, which therefore have less seeds per plant and longer cylce plants are generally bigger, and therefore have more seeds per plant. This is why 400,000 seeds are planted per hectare for short cylce varieties and only 350,000 seeds need to be planted per hectore for long cylce varieties to receive similar yields for the land being used.
The soybeans used at La Calendaria are all genetically engineered (GE) seeds. Though the soil at La Calendaria is typically depleted of nitrogen and phosphorus, the soybeans do not receive either of these mineral supplements for growth. The seeds are inoculated with a supplement that contains bacteria that improves the nitrogen production of the plants.
When fertilizer used to be cheaper, the administration used to purchase more phosphorus to use during the corn application so that it would last for the soybean crop that would follow the corn crop. By doing one application for both crops, it saved on the labour costs for application and supplemented both crops. Now that phosphorus is more expensive, only the quantities required for the corn crops are applied.
The growth phases of the soybean, as I understand them, are as follows: seeding, germination, flowering (plant is reproductive at the first flower), pollination, seed formation, seed maturation and drying.
Pests that are of concern to the soy plant are catipillars (in Spanish trips, tucuras, oruga bollifera) which eat the leaves of the plant, small spiders which toward the end of the plant life cycle consumes the leaves and the plants nutrients, and the chinca verde and its larvae which also eat the leaves. Pests are worse when the weather has high temperatures and low precipitation.
Leaf rust, a fungus, is the hardest to control and attacks when plants are subject to high temperatures and excessive humidity.
If the crop is going to be sold commercially, which means put to market for processing, more pests can be allowed than if the seeds are to be kept for seeding the following year. The generally acceptable organic material loss of a crop is about 15%. However, when monitoring the pest presence for a plot, it important to distinguish if the organic matter loss has occured slowly over time or over a short period of time - a 15% loss in a week can quickly turn into a 40% loss which is much more worrying.
There are a variety of pest and disease mitigation approaches. Luckily in this part of Argentina the crops aren't subject to many pests and disease becuase of the colder climate. Sometimes in fact the crops don't need an application of insecticide because the plants are strong enough to resist the pest and disease on their own. Otherwise insecticides, fungicides and herbicides are applied.
Applications of these protections are more preventative than curable, which is why there aren't often many pest or disease outbreaks in the crops - each harvest has chemical applications included in its production cost. If there is an outbreak of a pest or disease, the administration needs to evaluate if the market price at the time can support a chemical intervention cost wise. Rarely is this the case. As a result, they crop is just left to finish its growth cycle as is until complete, and then the seeds are harvested with accordingly lower yields than the healthy plots. (The quality of the soybeans are not affected by disease and pests, just the yields of the crop.)
Other technologies being developed include genetically engineering the plants to be toxic to the pests that threaten them. For example, there is a variety of soybean that has been developed to be toxic to the chinca verde and it's larvae.
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