For maintaining the fertility status of soil and conserving the water, different types of measures or practices exist; however, agronomical practices are more suitable for the drylands because these practices do not need high technical knowledge and initial costs. The major agronomic practices are contour cultivation, tillage, mulching, dead furrow, line sowing, broad bed furrow, strip cropping and improved dryland practices.
These measures help to intercept raindrops and reduce the splash effects, help better intake of rainwater, provide more opportunity time for rainwater to infiltrate into soil and help to reduce runoff generation due to perfect crop geometry.
The most common agronomical practices used for soil and water conservation, are discussed below:
Measure # 1. Contour Cultivation:
In contour cultivation, all agricultural operations such as ridging, ploughing, harrowing and sowing are recommended to be done on the contour wherever possible or at least generally across the direction of the slope where the land holdings are very small. Even though the operation is very simple, it plays a major role in retarding the process of soil erosion through runoff.
It conserves soil and water, and due to increased time of concentration, more rainwater seeps through the soil profile to recharge groundwater. Contour farming provides the greatest possibility for water conservation, and on the other side, it reduces soil loss by water erosion. The purpose of contour farming is to make the rows and tillage lines across the normal slopes.
The rows and tillage lines works as a protecting material for water to reduce its flow and provide more opportunity time to water to infiltrate into the soil. Contour farming is more important for the dryland areas where water and soil pose the main limitations for growing crops. The research undertaken at difference places with contour cultivation and cultivation along the slope showed that contour cultivation rather than cultivation along the slope reduced soil and water losses (Table 8.1).
Measure # 2. Dead Furrows:
In this practice, when all tillage operations are complete, one deep dead furrow (with closed ends) at every 3.6 meter interval is left. It should remain in position until the crop is harvested. Dead furrows help in reducing the runoff velocity and also conserve water. The dead furrow reduces the runoff generation from agricultural land and act as obstruction for the water flow and ultimately control soil and water erosion.
Measure # 3. Tillage Practice:
Tillage practice alters soil physical properties like porosity, bulk density, surface roughness and hardness of pans. Different types of tillage implements influence these physical properties in their own ways, and thus, affect soil erosion and enhance water conservation. Tillage practices can be divided into two categories, i.e. conventional and conservation tillage practices. Conventional tillage includes 2-3 ploughing followed by harrowing and planking.
It leaves no land unploughed and no residue on the field. Conservation tillage disturbs the field to a minimum necessary extent and leaves crop residue on soil surface. In this way, tillage practices reduce soil loss and conserve water.
In most of the cases, conservation tillage practices reduce soil loss up to 50% over conventional tillage practice. Hardpans induce runoff, and at the same time, reduce crop yield by restricting root growth. Sub-soiling improves soil moisture regime, reduces runoff and soil erosion, and increases yield of agricultural crops.
Sharma et al. (2013) reported that tillage practices in combination with mulching material enhanced soil moisture conservation over no till for sowing the succeeding wheat crop after harvesting of maize. Jat et al. (2012) also found that conservation tillage practices are the best-suited measures for controlling runoff and soil loss under maize cultivation. The effect of different soil moisture conservation treatments on runoff and soil loss is shown in Table 8.2.
Measure # 4. Mulching:
Mulch is the material, organic or mineral in nature such as saw dust, straw, paddy husk groundnut shell, crop residues, leaves, paper, stones, loose soil etc. spread on the surface of the soil in order to protect the soil from the impact of rain drops, avoid surface crusting, reduce evaporation, and thereby, to conserve soil moisture and reduce soil loss. Mulch also serves to moderate surface soil temperature. Mulch farming is a system of farming in which organic residues or other materials are neither ploughed into the soil nor mixed with it, but are left on the surface to serve as mulch. Mulch farming (Fig. 8.3) is not only useful for reducing soil and water loss but also for maintaining high soil moisture in the field soils.
Thus, mulching can be used in high rainfall period/region for decreasing soil and water loss and in low rainfall period/region for increasing soil moisture. In agricultural practices, it is the best to “grow the mulch in place”, that is to use residues in the same field where they grew earlier. Mulches are also applied in narrow slots (vertical mulching) instead of spreading on soil surface. Crop residues are pressed into narrow continuous slot of 5-10 cm width and 20-25 cm depth. The residue is filled up to 5 cm above the ground level.
These slots with residues form a ridge across the slope, and thus, these increase infiltration, reduce runoff and conserve soil and water resources.
Covering the soil surface with mulching material enhances availability of soil moisture content, irrespective of types of mulch namely organic or inorganic. Singh (2012) reported that the mulching is the best soil moisture conservation measure in ber orchard for increasing soil moisture. Vashisht et al. (2013) also observed lower runoff and soil loss in mulched plots over control, and also more water was conserved with mulched plot in soil profile than that without mulched plot during crop growth and harvest stages of crop (Table 8.3).
Measure # 5. Cropping Systems/Crop Rotations:
Soil and water conservation also depend on adopted cropping system. Crop rotation refers to growing of crops in an order in which the chosen cultivated crops follow one another in a set of cycle on the same field over a definite period of time for their growth and maturity with an objective to get maximum profit with least investment without impairing soil fertility.
It is a matter of common knowledge that the crop grown year after year on the same soil depletes soil fertility. Also line sown and clean tilled crops promote soil removal. Thick growing crops protect soil agent from the impacts of rain drops and also intercept runoff. A proper rotation of crops not only maintains fertility but also helps in reducing soil erosion and water loss.
A good rotation should include a cultivated row crop densely planted with small grain and a spreading legume. In multiple cropping systems, where the soil is covered with crops throughout the year, there may be runoff but soil loss is minimum as falling rain is intercepted by the crop. Experiments were undertaken at Vasad, Gujarat to evaluate the effects of four cropping systems on runoff and soil loss, and the results are presented in Table 8.4. It is clearly revealed that the soil loss is the minimum for the cropping system of pearl millet intercropped with green gram.
a. Strip Cropping:
Raising erosion permitting crops (EPC) namely sorghum, maize and millets with erosion resistant crops (ERC) like groundnut, moth bean, horse gram, having abundant adventitious root system and providing high percentage of canopy in strips in ratio of 2:1 or 3:1 (i.e. 20 to 10 rows or 30 to 10 rows), helps in trapping soil from erosion permitting crops strips to erosion resistant crop strips.
The increased resistance to runoff in ERC results in higher volume of water percolating through soil profile, due to increased time of (on-ground) concentration. The close-growing ERC strips are generally legumes which fix nitrogen in the soil and enrich it.
The canopy of the ERC also protects the soil from beating action of rain drops. Strip cropping also helps in stabilizing crop production. The width of erosion permitting crops (millets) and erosion resisting crops (pulses) may be used, as given in Table 8.5. However the spacing depends on the nature of soil and slope of the land. A view of the intercropping experiment undertake by the ICAR-Central Arid Zone Research Institute at Kukma, Bhuj with pearl millet as EPC and cluster bean as ERC.
The erosion resisting crop strips act by helping in the following way
1. Check the velocity of the runoff water coming the erosion permitting strips.
2. Act as a fliter and arrest the eroded soil within the close growing strips.
3. Allow water to remain for a longer time in the soil and Making it available to plant.
4. Provide physical protection against blowing by wind.
There are four types of strip Cropping- Contour strip- cropping; field strip –cropping; Wind strip cropping and Permanent or temporary buffer strip – cropping.
b. Smothering/Cover Crops:
Erosion from cultivated fields can be reduced, if the land has enough crop canopies during the peak season. Good ground cover canopy gives protection to the land like an umbrella. Cover crop is a close growing crop raised mainly for protection and maintenance of soil. Effectiveness of the cover crop depends on close spacing and development of good canopy for interception of rain drops so as to expose minimum soil surface for erosion. Major role of plant cover is to protect the soil from the force of falling rain drops which is the primary cause of erosion on cultivated land.
The rain drops have energy and they scribe the bare soil, dislodge particles from the soil mass. These soil particles get lost through runoff. Plant cover controls splash erosion by intercepting the rain drops and absorbing their kinetic energy. Pulse crops are generally more suitable for such purposes. Bean as a cover crop in combination with mechanical measures reduces soil and water loss in tea plantation.
c. Plantation of Nitrogen Fixing Legume Crops:
Introduction of short duration legume crops in rotation may be helpful in reducing the nitrogen requirement of cereals. The symbiotic genus rhizobium commonly associated with the leguminosae has been recognized for its contribution to the nitrogen fixed by legumes in the growing season which varies widely from a few kg to 200-300 kg or even more (Berseem etc.).
The shortage of fertilizer, thus, could be to some extent taken care of by the residual nitrogen left in the soil. A large part of the fixed nitrogen is utilized by the plant for its growth and development which gives better cover on the land, good protection to soil from beating action of rain and reduces soil erosion. A fairly good amount of nitrogen is also released to the soil which is made available to the succeeding crop.
d. Mixed/ Intercropping:
It is a practice of growing more than one crop in the same field simultaneously. In this practice, there is one main crop and one or two subsidiary crops. Generally, legume is used as one of the crops. This system of cropping is very extensively adopted by the farmers in India.
This practice gives better cover on the land, good protection to soil from beating action of rain and protection from soil erosion, by binding the soil particles. Growing soybean, groundnut, cowpea etc. with maize, sorghum, pearl millet, etc. is a common example of this practice. Jat et al. (2010) observed that intercropping of maize and black gram (4:8 row ratio) with summer deep ploughing and ridging after first intercultural operation recorded least runoff and soil loss over rest of the treatments (Table 8.6).
e. Green Manuring:
Green manuring can be defined as a practice of ploughing or turning green plants/vegetation into the soil for the purpose of improving physical structure as well as fertility of the soil. These green plant tissues provide stable soil aggregate, good aeration, add more organic matter and enhanced beneficial microbial activities into soil after decomposition which either directly or indirectly helps in conserving soil and water resources. However, the applicability of these practices in some parts of arid region is limited due to shortage of water necessary for decomposition. There are two types of green manuring.
i. In Situ Green Leaf Manuring:
In this system, green manure crops are grown and buried in the same field which is to be green manured. The most common green manure crops grown under this system are sunhemp (Crotalaria juncea), dhaincha (Sesbania aculeata), greengram and cowpea etc.
ii. Ex-Situ Green Leaf Manuring:
Green leaf manuring refers to turning into the soil green leaves and tender green twigs collected from shrubs and trees grown on bunds, waste lands and nearby forest area. This system is generally followed in southern India. The common shrubs and trees used are- Glyricidia (Glyricidia maculata), Sesbania speciosa, Karonj (Pongamia pinnata). Green manuring adds organic matter to the soil and improves its structure; it facilitates the penetration of rainwater into the soil profile, and thus, decreases runoff and soil erosion. Besides, it increases the availability of certain plant nutrients like phosphorus (P2O5), calcium, potassium, magnesium and iron.
f. Line Sowing:
Sowing of crops in line with the help of sowing implements is called line sowing. In this system, crop seeds are sown in line and covered with loose soil for good germination and further growth. During the runoff generation, these lines act as a vegetative barrier and obstruct the water flow which is responsible for soil and water loss. By sowing of crops in line, water loss as runoff in the field may be conserved as the lines reduce the velocity of runoff and provide more opportunity time to water to infiltrate into soil.
g. Broad Bed Furrow System:
In broad bed furrow (BBF) system of farming, broad bed is formed between two furrows. The beds are used for crop growing, whereas furrows are used for carrying excessive runoff which reduce soil loss and increase water storage into soil profile. The broad bed furrow system has been developed at the International Crops Research Institute for Semi-Arid Tropics (ICRISAT) in India.
A comparative research programme was carried out on station for eight years before being taken for on farm adaptive research at Tadthanapalle in Medak District. It is a modern version of very old concept of encouraging controlled surface drainage by forming the soil surface into beds. The recommended ICRISAT system consists of broad bed of about 100 cm wide separated by sunken furrows of about 50 cm wide.
The preferred slope along the furrow is between 0.4 and 0.8 percent on vertisols. Two, three or four rows of crops can be grown on the broad bed, and the bed width and crop geometry can be varied to suit the cultivation and planting equipment. The BBF system increases soil moisture storage into soil profile 1% higher than that in flat bed system.
h. Use of Chemicals:
Breakdown of soil aggregates by falling rain drops is the main cause of detachment of soil particles. Soil with stable aggregate resist break down, and thus, reduce soil erosion. Aggregate stability can be increased by spraying chemicals like polyvinyl alcohol at 480 kg ha-1 however; it depends on type of soil. Soil treated with bitumen increase water stable aggregate and infiltration capacity of soil. However, practical method of increasing stability of aggregates is by application of organic matter, farmyard manure, crop residues and green manure.
i. Other Agronomic Practices:
Several other agronomic practices help in soil and water conservation either by increasing infiltration or by providing more opportune time for infiltration or by improving soil physical properties or by decreasing soil detachment of soil particles. Application of manure and fertilizer provide early crop cover due to early growth.
Crop production on eroded soil under dryland condition is limited not only due to inadequate moisture, but also due to poor fertility status of soil. Fertilizer application increases the yield of several crops on eroded soil. Response to fertilizer application is more with soil conservation practices and placement of fertilizers.