Agriculture Reference
In-Depth Information
translated to yield increases of 20-70 kg ha
−1
for wheat, 10 -50 kg ha
−1
for rice, and 30-300 kg ha
−1
for
corn. Weil and Magdoff (2004) successfully isolated SOM effects on crop yields; hence crop rotation
was imposed to alter SOM for 20 years, and then all plots were treated alike for 2 years. They found
SOM levels to account for 82-84% of the variation in corn yields during these 2 years.
Strickling (1975) suggested that the influence of SOM on soil aggregation enhanced water infil-
tration and, consequently, crop yields. Weil and Magdoff (2004) reported that SOM is a key deter-
minant of soil quality because it influences nutrient holding and exchange, soil structure, erosion,
resistance, and biological processes such as N mineralization. All these soil properties are associ-
ated with crop yield improvement (Fageria and Gheyi, 1999). Brady and Weil (2002) reported that
small quantities of both fulvic and HAs in soil solution are known to enhance certain aspects of
plant growth. Components of these humic substances probably act as regulators of specific plant
growth functions, such as cell elongation and lateral root initiation (Brady and Weil, 2002).
4.11 CONCLUSIONS
A major part of nitrogen is taken up from the organic substances of the soil during crop growth. The
SOM content of the soils is also related to crop productivity. Hence, a discussion on OM manage-
ment in crop production is very pertinent here. SOM is a heterogeneous and dynamic soil compo-
nent that varies in molecular structure, decomposition rate, and turnover time and exerts a major
influence on soil quality and the global C cycle. Its role in improving the crop productivity and sus-
tainability of agricultural systems is enormously high. OM modifies the soil physical, chemical, and
biological properties in favor of better soil quality and, consequently, higher crop yields. A substan-
tial amount of N requirements of the plants is satisfied from the mineralization of SOM. The pool
sizes of SOM are soil specific, while their mineralization rate constants vary with environmental
conditions. Plant and animal residues are the major sources of OM formation in the soil. SOM for-
mation and accumulation is, however, highly dependent on management practices and the amount
and placement of organic materials. For example, improving SOM with CT in crop production is
difficult due to the rapid decomposition of organic materials by microbial action and loss of soil
carbon, especially under tropical conditions. However, soil characteristics are improved with the
addition of organic materials to the soil, which are in favor of higher crop yields. Adopting appro-
priate soil and crop management practices can be helpful in improving and/or stabilizing SOM of
soils. These practices are the use of appropriate crop rotation, adoption of conservation or minimum
tillage, and application of farmyard and compost manures and liming acid soils. In addition, the use
of an adequate rate of fertilizers can also improve the OM content of soils by increasing the shoot
and root biomass. SOM is a storehouse for slow release of essential plant nutrients that also reduces
their leaching to groundwater.
Heavy metals are important environmental pollutants threatening the health of man, animal, and
agroecosystems. The fate of heavy metals in the soil-plant systems is largely controlled by sorption
reactions with soil colloids. The SOM owing primarily to higher CEC and to form inner-sphere com-
plexes through surface reactions groups, important sorbent of heavy metals. Thus, decreasing their
toxicity to crop plants in heavy metal contaminated soils as well as inhibited their leaching to ground-
water. SOM also adsorbs herbicides and prevents their leaching to groundwater. In addition, SOM
stores a large amount of C in the soil and avoids CO
2
escape into the atmosphere. Hence, OM plays
an important role in reducing global warming or in greenhouse effects and environmental pollution.
REFERENCES
Abbott, J. L. and T. C. Tucker. 1973. Persistence of manure phosphorus in calcareous soil.
Soil Sci. Soc. Am.
Proc.
37:60-63.
Acosta-Martinez, V., T. M. Zobeck, and V. Allen. 2004. Soil microbial, chemical and physical properties in
continuous cotton and integrated crop-livestock systems.
Soil Sci. Soc. Am. J.
68:1875-1884.
