**6.1 Biological measures (agronomic/agricultural and agroforestry)**

Agronomic measures are applicable in the landscape of ≤2% slope. Agronomic measures reduce the impact of raindrops through the covering of soil surface and increasing infiltration rate and water absorption capacity of the soil which results in reduced runoff and soil loss through erosion [39]. These measures are cheaper, sustainable, and may be more effective than structural measures, sometimes [4]. Important agronomic measures are described below.

#### *6.1.1 Contour farming*

*Soil Moisture Importance*

loss is 12.0 tons ha<sup>−</sup><sup>1</sup>

given in **Figure 2** [21].

water erosion [13].

fields [28]. Further, around 45.9 kg C ha<sup>−</sup><sup>1</sup>

eroded soil during the month of July [29].

results in annual total soil loss of 5334 million tons (m t) and nutrient loss of 8.4 m t throughout the country [17]. However, the mean annual permissible limit of soil

sea, while 61% is transported by runoff from one place to another and the remaining 10% is directly deposited in reservoirs [21]. Higher nutrient concentration has been recorded in soil samples collected from runoff loads over the soil of agricultural

The soil organic matter (SOM) is vital for improving soil bio-physico-chemical properties and contains nearly 95% of N and 25–50% of phosphorus [30]. Higher rate of erosion results in loss of soil and fine organic particles. The soil removed by erosion has 1.5–5 times higher SOM than the soil left behind [31]. The availability of SOM also affects the biological activities and soil biodiversity in a particular agro-ecosystem. Moreover, the intensive and erratic rainfall results in higher soil erosion which leads to reduced infiltration and eventually less water availability to the vegetation. Sharda et al. studied the impact of the harshness of water erosion on agricultural productivity and advocated that water erosion reduced the annual crop production by 13.4 Mt in 2008–2009 at the national level [32]. Thus, the soil loss by water and wind severely affects the productive efficiency of all ecosystems [17, 33, 34]. The comprehensive impacts of erosion on soil and water resources which are liable to reduce agricultural productivity are

The vegetation cover is imperative for moderating surface runoff and water erosion from agricultural lands [35]. The rate of runoff, soil, and nutrient loss is predominantly determined by the type of vegetation, canopy cover, slope gradient, and rainfall characteristics [36]. The higher canopy cover and crop residues mulching on soil surface results in the reduced rate of surface runoff and also reduces the impact of rainfall erosivity and soil erodibility [13, 35, 37]. Vegetation cover reduces the detachment of soil particles along with the protection of soil surface from intensive rainfall. Moreover, it also conserves soil moisture and retains sediment and organic materials [38]. To sustain agricultural productivity, it is imperative to reduce runoff, soil loss, and nutrient loss through

. Out of total eroded soil around 29% is permanently lost to the

and 4.3 kg N ha<sup>−</sup><sup>1</sup>

were recorded in

**30**

**Figure 2.**

*Impact of erosion on soil and water resources.*

Contour farming is one of the most commonly used agronomic measures for soil and water conservation in hilly agro-ecosystems and sloppy lands. All the agricultural operations viz. plowing, sowing, inter-culture, etc., are practiced along the contour line. The ridges and furrows formed across the slope build a continual series of small barriers to the flowing water which reduces the velocity of runoff and thus reduces soil erosion and nutrient loss [40, 41]. It conserves soil moisture in low rainfall areas due to increased infiltration rate and time of concentration, while in high rainfall areas, it reduces the soil loss. In both situations, it reduces soil erosion, conserves soil fertility and moisture, and thus improves overall crop productivity. However, the effectiveness of this practice depends upon rainfall intensity, soil type, and topography of a particular locality.

### *6.1.2 Choice of crops*

The selection of the right crop is crucial for soil and water conservation. The crop should be selected according to the intensity and critical period of rainfall, market demand, climate, and resources of the farmer. The crop with good biomass, canopy cover, and extensive root system protects the soil from the erosive impact of rainfall and create an obstruction to runoff, and thereby reduce soil and nutrient loss. Row or tall-growing crops such as sorghum, maize, pearl millet, etc. are erosion permitting crops which expose the soil and induce the erosion process. Whereas close growing or erosion resisting crops with dense canopy cover and vigorous root system viz. cowpea, green gram, black gram, groundnut, etc. are the most suitable crops for reducing soil erosion [42]. To increase the crop canopy density, the seed rate should be always on the higher side.

### *6.1.3 Crop rotation*

Crop rotation is the practice of growing different types of crops in succession on the same field to get maximum profit from the least investment without impairing the soil fertility. Monocropping results in exhaustion of soil nutrients and deplete soil fertility. The inclusion of legume crops in crop rotation reduces soil erosion, restores soil fertility, and conserves soil and water [43]. Further, the incorporation of crop residue improves organic matter content, soil health, and reduces water pollution. A suitable rotation with high canopy cover crops helps in sustaining soil fertility; suppresses weed growth, decreases pests and disease infestation, increases input use efficiency, and system productivity while reducing the soil erosion [42].
