Manure is a natural material, obtained by decaying plant and animal waste, that can be applied to the soil to enhance its fertility. Manure usually consist of faeces and urine of domestic livestock, with or without accompanying litter such as straw, hay, or bedding. The most common sources of manure are cows, horses, sheep.

The organic manure contains a high amount of organic matter which increases the capability of the soil to hold the water. They are prepared by the decomposition of the organic matter by the microbes. They are highly rich in the plant nutrients. They also help to improve the quality and texture of the soil. The gaseous exchange takes place easily in this soil which allows the germination and growth of the plants properly. 

Statements I and ii are correct. Rhizobium leguminosarum is also known as Bacillus radicicola. Nitrifying bacteria (Nitrosomonas, etc) are chemoautotrophs. They use inorganic energy sources. However, the enzyme nitrogenase is highly sensitive to oxygen and gets readily oxidised in it's presence and Leghaemoglobin creates anerobic conditions for the enzyme nitrogenase by scavenging the oxygen molecules.

So, the correct option is 'A-(ii), B-(iii), C-(iv), D-(i)'.

Leghemoglobin supports the centralization of free oxygen in the cytoplasm of contaminated plant cells to guarantee the best possible capacity of root knobs. Its capacity is to help give oxygen to the breathing harmonious bacterial cells in root nodules of leguminous plants in a way practically equivalent to hemoglobin transporting oxygen to breathing tissues in creatures.

Soya bean is a legume. Leguminous plants contain root nodules. Nitrogen fixing bacteria rhizobium is present in the root nodules of leguminous plants which fix the nitrogen naturally. So, it does not require an outer supplement for nitrogen or nitrogen fertilizer.

Leghaemoglobin is a hemoprotein found in the root nodules of leguminous plants.  In plants colonized by Rhizobium, such as alfalfa or soybeans, the presence of oxygen in the root nodules would reduce the activity of the oxygen-sensitive nitrogenase, an enzyme responsible for the fixation of atmospheric nitrogen.   

There are different methods by which nutrients in the soil can be replenished. Fertilizers and manures contain plant nutrients such as nitrogen, phosphorus, potassium. Fertilizer can be added to the soil. It helps in replenishing exhausted soils with rich sources of organic nutrients. Manure is environment friendly and replenishes the soil with organic nutrients. Compost is decomposed organic material. It reintroduces living organisms and nutrients in the soil. It improves soil structure and provides a healthy environment for plant roots. 

Azolla and BGA are used as biofertilizers in the rice field because they increase the yield of the paddy or rice by supplying the plant with all the nutritional elements

Through the use of biofertilizers, healthy plants can be grown, while enhancing the sustainability and the health of the soil. ... Biofertilizers such as Rhizobium, Azotobacter, Azospirilium and blue green algae (BGA) have been in use a long time. Rhizobium inoculant is used for leguminous crops. So, the correct option is "B" (Biofertilizers).

Heterocysts are specialized nitrogen-fixing cells formed during nitrogen starvation by some blue-green algae. They fix nitrogen from di-nitrogen in the air using the enzyme nitrogenase and nitrogenase is inactivated by oxygen, so the heterocyst must create a micro-anaerobic environment and that's why heterocysts degrade photo-system II, which produces oxygen.

• Leghaemoglobin (also leghemoglobin or legoglobin) is an oxygen carrier and hemoprotein found in the nitrogen-fixing root nodules of leguminous plants. 
• Leghaemoglobin buffers the concentration of free oxygen in the cytoplasm of infected plant cells to ensure the proper function of root nodules.

So, the correct answer is "transports oxygen to the root nodule".

Microorganisms which, when applied to seed, plant surfaces, or soil, colonizes the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant. Rhizobium can be used as biofertilizer. Rhizobium are found in the soil and after infection, produce nodules in the legume where they fix nitrogen gas (N2) from the atmosphere turning it into a more readily usable form of nitrogen.

Mycorrhizal fungi, which form a symbiosis with the roots of nearly all vascular plants, play a key role in solving the phosphate shortage problem for plants. Mycorrhizal fungi can effectively increase phosphate uptake by converting insoluble phosphates to soluble, available forms.

Leg-haemoglobin is an oxygen carrier. It is found in root nodules of leguminous plants. It is red in colour and is a hemoprotein. It provides or helps in providing oxygen to symbiotic bacterial cells. 

Leghaemoglobin helps to mantain internal oxygen in symbiotic nodules, because this protein has ten times more affinity for oxygen as compared to blood pigment haemoglobin.Therefore they acts as oxygen scavenger.

Rhizobium is microaerophilic rod shaped gram negative bacteria found in association with legume plants in root nodules. These bacteria fix atmospheric nitrogen into ammonium ions, which can be readily assimilated by plants.

Plants cannot consume atmospheric nitrogen directly, because in atmosphere nitrogen occurs in stable diatomic form. The atmospheric nitrogen needs to be converted into plant usable forms like nitrate, nitrite and ammonium ion. This process is called as nitrogen fixation. 

Nodules develop in the roots of leguminuos plants like pulses and grams. These nodules have a very specific function. They inhabit rhizobium bacteria. it is a type of nitrogen fixing bacteria, It absorbs free nitrogen from the atmosphere and converts it into nitrites and nitrates and fixes it in the soil. From soil, plants absorb nitrogen fixed by the bacteria. So, nitrogen requirement of leuminuous plants is fulfilled.

In the roots of legumes, there live many bacteria, who through their own metabolic processes are able to convert the nitrogen gas into ammonia or ammonium, depending on the acidity of the soil. Converting nitrogen gas into a more usable form is extremely difficult and is the reason that this process is so specialized. While ammonium may be usable by a few plants, the majority cannot use it and another process is required. Nitrifying bacteria oxidize the ammonia creating nitrite then nitrate allowing for the nitrogen to be assimilated into the plants.

Many rhizobia, nitrogen fixing bacteria, live in a symbiotic relationship with plants known as legumes. In such plants, the presence of oxygen in the root nodules would reduce the activity of the oxygen-sensitive nitrogenase. In these situations, the roots of such plants produce a protein known as leghemoglobin. Leghemoglobin buffers the concentration of free oxygen in the cytoplasm of infected plant cells to ensure the proper function of root nodules. Leghemoglobin is a nitrogen or oxygen carrier; naturally occurring oxygen and nitrogen interact similarly with this protein. Hence option B is correct.

A chemical fertilizer/artificial fertilizer is defined as any inorganic material of wholly or partially synthetic origin that is added to soil to sustain plant growth. Organic fertilizers are substances that are derived from the remains or byproducts of natural organisms which contain the essential nutrients for plant growth.

Leghaemoglobin is an oxygen scavanger. It combines with oxygen and protects nitrogenase, which catalyses the fixation of nitrogen under anaerobic conditions.

Biofertilizer is a substance that contains living organisms which is used to increase the fertility of the soil. It improves the growth of plant by increasing the content of the soil and thereby increasing the availability of nutrients to the host plant. Also, it does not allow pathogens to flourish. Various biofertilizers are Rhizobium, Azotobacter, blue green algae (BGA). They live in symbiotic association with the plants and provides nitrogen to the plant. 

Traditionally, cowdung is used as a fertilizer. It provides growing medium for plants. It is nutrient-rich fertilizer. It is either mixed into the soil or used as top dressing. However, methane (greenhouse gas) is emitted from cowdung when it is processed. Hence, it is replaced by biofertilizers. Biofertilizers are substances which contains live organisms and are used to increase fertilizer of the soil. Examples of biofertilizers include rhizobium, azotobacter, azospirillum and blue green algae(BGA).

Biofertilizer is a substance that contains living organisms which is used to increase the fertility of the soil. It improves the growth of plant by increasing the availability of nutrients to the host plant. Various biofertilizers are Rhizobium, Azotobacter, blue green algae (BGA). Algae have ability of nitrogen fixation, therefore adding organic matter and extra nitrogen to the soil. This increases the soil fertility. 

Leguminous plants are in symbiotic association with nitrogen-fixing bacteria like Rhizobium. These bacteria invade root hairs of leguminous plants and forms root nodules in which they fix nitrogen. A red pigment present in the root nodules of leguminous plants is known as leghaemoglobin. Leghaemoglobin is an oxygen-carrier molecule.  It protects nitrogen-fixing enzyme nitrogenase from the side effect of oxygen as the enzyme is highly sensitive to oxygen.

Legumes are in symbiotic association with nitrogen-fixing bacteria like Rhizobium. They fix nitrogen with the help of bacteria that live in their roots. These bacteria invade root hairs of leguminous plants and forms root nodules in which they fix nitrogen. Rood nodules are found in some other plants also apart from leguminous plants. A red pigment present in the root nodules of leguminous plants is known as leghaemoglobin. 

Atmospheric nitrogen is not available to the plants. Nitrogen fixing bacteria converts atmospheric nitrogen into ammonium compounds and make it available to the plants. There are two types of bacteria, free-living and symbiotic. Example of free living nitrogen fixing bacteria include Azotobacter. The example of symbiotic nitrogen fixing bacteria includes Rhizobium. Rhizobium lives in symbiotic association with the legume plants in the root nodules and fixes atmospheric nitrogen. Root nodules of legume plants contains leghaemoglobin. This acts as an oxygen scavanger. 

Leguminous plants are in symbiotic association with nitrogen-fixing bacteria like Rhizobium. These bacteria invade root hairs of leguminous plants and forms root nodules in which they fix nitrogen. A red pigment present in the root nodules of leguminous plants is known as leghaemoglobin. Leghaemoglobin is an oxygen-carrier molecule.  It protects nitrogen-fixing enzyme nitrogenase from the side effect of oxygen as the enzyme is highly sensitive to oxygen.

Crotalaria juncea and Alhagi camelorum are used as green manure in crop fields and sandy soils because these plants, when grown, replenish the soil with sufficient nutrients and nitrogen content after its usage by the crop plant.

The root nodules of the leguminous plants contain an oxygen-binding heme protein called leghemoglobin. It is present in the cytoplasm of infected nodule cells at high concentrations. The function of  leghemoglobin is to help transport oxygen to the respiring symbiotic bacterial cells in a manner analogous to hemoglobin transporting oxygen to respiring tissues in animals. It has a high affinity for oxygen (approximately, ten times higher than the ß chain of human hemoglobin). Thus, it acts as a oxygen scavenger.
Hence, the correct answer is option (A).

The root nodules contain pink colored pigment contains a protein called leg-hemoglobin.

Leghaemoglobin is an oxygen carrier found in the nitrogen fixing root nodules of leguminous plants. Rhizobium is a free living bacteria that can fix atmospheric nitrogen.

Leghaemoglobin present in plant nodules ,impart a characteristic pink colour to the roots.

Protozoa play a major role in replenishing nutrients in the soil. Protozoa have a lower concentration of nitrogen in their cells than the bacteria they eat. Therefore, they obtain and utilize the amount of nitrogen needed and release the excess in the form of ammonium, thereby making it available for use by plants and other soil organisms.   

Plants are not capable of fixing nitrogen on their own, but need it in one or the other form to make proteins and amino acids. Legumes form root nodules, when they exist in a symbiotic relationship with 'Rhizobia' and therefore, have high levels of nitrogen available to them. These soil bacteria (e.g., Rhizobium, Mesorhizobium, Sinorhizobium) fix the atmospheric nitrogen or dinitrogen, into inorganic compounds, like ammonium, which is then converted into amino acids, which the plants can utilize.

• Those fertilizers which get decomposed naturally are known as natural fertilizers whereas those which are human-made are known as chemical fertilizers. 
• Natural fertilizers include compost, animal waste, dead organisms, etc. Chemical fertilizers include inorganic materials. 
• Chemical fertilizers are directly available whereas natural fertilizers need to be prepared. Chemical fertilizers contain different chemical so they affect the pH value of soil whereas natural fertilizers don't.
  
  

Rhizobium, is a rod shaped, aerobic, nitrogen fixing bacterium present in the root nodules of leguminous plants. It performs symbiotic nitrogen fixation in the root nodules of leguminous plants, in presence of an enzyme dinitrogenase.

So, the correct option is ‘bacteria are aerobic and nitrogenase are active’.

Larger surface area and thinner walls of root hair are required to absorb water efficiently. 

The cells of the roots contain cell sap (solution) at a higher concentration than that of surrounding soil water. As a result, the water is absorbed by the root hairs. This is because the water always travels from a region of high water potential to the region of lower water potential. Here, the soil possesses a higher water potential as compared to the root hair.

Transpiratioal or gravitational pull exert strain so they are factors that can cause rupture of the column. 

Phosphorus, sulphur, nitrogen and potassium most readily mobilise while calcium is structural component which is not remobilised.