Agriculture Reference
In-Depth Information
change dramatically from year to year. Some years may be droughty while others may
have excessive rainfall. Also wind events can be highly variable, although there are
some areas of the world where there are monsoon seasons with high rainfall and
typhoon seasons with high wind. In the northern Philippines there is no, or very low,
rainfall December through March while May through August, the monsoon season,
will have very high rainfall.
8.5.1 Excess Precipitation
Excess precipitation just before, during, or after the growing season can be very detri-
mental to crop production. On a large scale excess precipitation can cause excessive
soil erosion and mud slides and prevent farmers from preparing fields for planting. It
can also saturate soil, filling all the pore space with water and thus depriving plant
roots of oxygen.
†
In addition it can provide an environment conducive to enhanced
growth of fungi and various plant pathogens and deleterious insects. At harvest
heavy rains may knock down plants and lead to spoilage of grain in the field. It will
also lead to a need for increased drying time once the grain is harvested. All may
lead to a decrease in yield.
8.5.2 Deficient Precipitation
Deficient rainfall during the growing season, in areas not suitable for irrigation, is
commonly referred to as a drought. Typically, drought is thought of as insufficient
water, either as rainfall or as stored water in the ground, at any stage of the
growing season. If there are droughty conditions before planting, lack of soil water
may delay germination and the emergence of plants. Thus farmers may delay plant-
ing, hoping that precipitation will come. Dry conditions during the growing season
will decrease yields and will decrease fertilizer efficiency. It may also interfere
with pollination and the size of the grain heads. However, once the grain has fully
filled the head, an extended dry spell will be beneficial to harvesting and storage
of grain.
Drought and Alfalfa
Alfalfa is a deep-rooted, 150
þ
cm deep, legume commonly grown as a pasture or
hay for animals. An alfalfa field that had a deep soil with a clay subsoil experi-
enced a prolonged dry season. During this drought, the alfalfa was able to
draw water from deep in the soil profile while the common weeds in the field
were not. The consequence of this drought was that the alfalfa field was almost
completely free of weeds.
†This is true of most crop plants except lowland rice and taro, which are commonly grown with roots
submerged in water.
