Soil fertility
• Capacity of soil to provide all essential elements for specific crop production in an easily available form & in proper proportion. • In this case, scientists are more concerned with N status of the soil
Soil productivity
- Capacity of soil to produce maximum yield of a specified plant/crop or a sequence of crop under specified system of management.
- It is more than soil fertility.
- In addition, a productive soil for a specific crop may not be productive for other crop.
- Not all fertile soil may be productive due to other factors like water logging, drought, pH, microorganisms etc.
DIFFERENCE BETWEEN SOIL FERTILITY AND SOIL PRODUCTIVITY
PROBLEMS OF SOIL FERTILITY IN NEPAL :
→People in Nepal have been cultivating the crops since the advent of agriculture system. Manures are added to the soil from early times. With the increase in population, feeding requirement has increased many folds. For this, the importance of soil fertility has drawn the attention of all concerned. The green revolution has been quite successful in producing more cereals and other feeding stuffs. However, fertility problems is the major issue in the present situation.
The various fertility problems that is found in Nepalese soils are:
- The deficiency of major plant nutrients (N,P,K) in the soil.
- The use of different fertilizers in different types of soils for different crops.
- The requirement of more fertilizers for the new varieties of high yielding crops.
- High soil erosion in sloppy lands of hilly and mountainous regions.
Soil fertility status of Nepal
Soil fertility status as presented in workshop by DOA in collaboration with JICA (Japan International Cooperation Agency) shows that majority ( over 90%) of soils in Nepal fall in to the low to medium classes with respect to OM and Total Nitrogen status. Also, a good proportion of soils (55%) are acidic in nature while the majority tends not to be low in available P or exchangeable K.
Based on the study conducted at various RARC (Regional Agriculture Research Centre), B, Cu, Zn, Mo were observed to be low in nearly all districts of Nepal with the exception of Iron and Manganese contents in soil.
However, the research on micronutrients are limited in Nepal. The thorough study of all the nutrients should be needed to address the scenario of Nepalase soils.
BASIC TERMINOLOGY
Infiltration and Run-off:
Infiltration is process by which the portion of the precipitation that reaches the Earth’s surface through the seepage from the ground.
Precipitation that reaches the surface of the Earth but does not infiltrate the soil is called runoff.
Infiltration occurs when surface water enters the soil. This process is similar to pouring water onto a sponge. The sponge soaks up the water until it can hold no more. When this happens, we get overflow in the form of runoff, which is when surface water flows over land.
It means the infiltration occurs till the water can hold the water but when this capacity is drained, it cannot hold it for the long time and thus water flows over which is runoff.
Groundwater movement:
- The groundwater slowly moves through the spaces and cracks between the soil particles on its journey to lower elevations. This movement of water underground is called groundwater flow/movement.
- Groundwater begins as rain or snow that falls to the ground. This is called precipitation. Only a small portion of this precipitation will become groundwater. Most will run off the land surface to become part of a stream, lake or other body of water.
- The water that well draws from under the ground is an example of groundwater. Water that exists beneath the earth's surface in underground streams and aquifers.
Irrigation and drainage:
- Irrigation is the process of applying water to the crops artificially to fulfil their water requirements. Nutrients may also be provided to the crops through irrigation.
- The various sources of water for irrigation are wells, ponds, lakes, canals, tube-wells and even dams.
- Irrigation offers moisture required for growth and development, germination and other related functions
- .Drainage refers to the removal of excess water from the ground surface as well as from the subsurface soil to facilitate the proper growth of plants and to avoid the hazards due to water logging.
Wetland soils:
Wetlands are areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season.
Wetland soils impact directly on other wetland characteristics, e.g. water quality, fauna or vegetation, and can be a reflection of the physical processes occurring in the wetland, e.g. water inflow, water chemistry or filtering of pollutants.
Wetland soils can be identified using soil morphological indicators such as:
the accumulation of organic matter
gleyed soil colours (greenish-blue-gray)
soil mottling
iron or manganese segregations
oxidising root channels and soil pore linings
reduction of sulphur and carbon (e.g. acid sulfate soils).
Leaching:
Soil leaching is the movement of nutrient elements from topsoil through the soil profile.
Leaching causes significant nutrient losses, particularly in humid regions with high precipitation.
Leaching is a natural process caused mainly by precipitation, acidification and nitrogen saturation.
When leaching removes too much nitrate content from the soil, however, the pH drops too far and the soil become over-acidic.
Nitrogen leaching in soil can be minimized by following crop rotation, using organic manure and split doses of nitrogen application.
Field capacity:
Field capacity is the water remaining in a soil after it has been thoroughly saturated and allowed to drain freely, usually for one to two days.
How to calculate field capacity of soil?
1) fill a bare soil area with excess water inducing drainage.
2) cover the wet soil with a plastic cover
3) wait about 2-3 days
4) collect a soil sample
5) weigh moist soil, dry in a oven at 105°C till to constant; weigh (after about 24 hours) and weigh the dry soil.
6) Calculate moisture at field capacity.