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The present experiment was conducted during 2018-19 under the ongoing All India Coordinated Research Project on Long-term Fertilizer Experiment with soybean-wheat cropping sequence since 1972 at the Research Farm of Department of Soil Science and Agricultural Chemistry, Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur, Madhya Pradesh, India. The microbial properties and nitrogen (N2) fixation of soil under different nutrient combinations were studied in a 46-year old long-term fertilizer experiment in a Vertisol. The experiment was conducted in a randomized block design comprising of 10 treatments viz., T1: 50% NPK, T2: 100% NPK, T3: 150% NPK, T4: 100% NPK + Hand weeding (100% NPK+HW), T5: 100% NPK + zinc (100% NPK + Zn), T6: 100% NP, T7: 100% N, T8: 100% NPK+ 5 t FYM ha-1 (100% NPK+FYM), T9: 100% NPK(–S) and T10: Control, each treatment being replicated four times in a randomized block design. Soil samples from all the treatments were collected from 0–15 cm depth and microbial properties and N2 fixation of soil were estimated. Significant increase in soil organic carbon, total N and available N were recorded with 100% NPK+FYM. Similarly, the maximum number of nodules and their biomass were also recorded in 100% NPK+FYM treatment at 30, 45 and 60 days after sowing. The bacteria, fungi and actinomycetes population counts in soil were 39.1×107, 42.7×104 and 39.1×105 cfu g-1 soil, respectively with the integrated application of inorganic fertilizer and organic manure (100% NPK+FYM) over control (11.7×107, 18.5×104 and 13.6×105 cfu g-1 soil, respectively). Further, the conjoint use of balance dose of fertilizers with FYM was also significantly superior in terms of soil microbial biomass carbon and microbial biomass N over other treatments even after 46 years of experimentation. The grain and straw yield of soybean and their N uptake were also significantly increased with graded dose of fertilizers and maximum yield and N uptake were noted in 100% NPK+FYM treatments over control plot.

The present investigation was aimed at distribution of nitrogen (N) fractions in a 44-year-old (1972–73 to 2016–17) long-term fertilizer experiment on soybean-wheat cropping system in a Vertisol. The experiment included eight treatments comprising of different doses of fertilizers viz. 50% NPK, 100% NPK, 150% NPK, 100% NP, 100% N, 100% NPK + 5 t FYM, 100% NPK(−S) and control and replicated four times in a randomized block design. The applications of 100% recommended dose of fertilizers (NPK) with organic manure (5 t FYM ha−1) led to significant increases in organic carbon, total N, hydrolyzable-N (i.e., amino acid-N, hydrolyzable NH4+-N, hexose-amine-N) and non-hydrolyzable-N in both soil depths (0–15 and 1530 cm) as compared to control plot and their concentration was decreased with increasing soil depth. The result clearly indicates that both surface (0–15 cm) and sub-surface (15–30 cm) soil layers substantially contributed to the N requirement of soybean and wheat. The contents of various organic N fractions were higher in organic manure compared to untreated plots. The study revealed significant correlations of soil N mineralization with amino acid and hexose-amine-N fractions at 0–15 cm depth and hydrolyzable NH4+-N and amino acid-N fractions at 15–30 cm. Grain yields of soybean and wheat showed better correlations between amino acid-N in surface and hydrolyzable NH4+-N in the sub-surface soil layers with yields of soybean and wheat.

The present investigation was conducted during 2013–14, under an ongoing long-term fertilizer experiment (LTFE) with soybean-wheat cropping system, since 1972 at the Research Farm of Department of Soil Science and Agricultural Chemistry, Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur, Madhya Pradesh, India, under the aegis of All India Coordinated Research Project on Long-term Fertilizer Experiments. The chemical and biological properties of soil under different nutrient combinations were studied in the 41-year old LTFE in a Vertisol. The experiment was conducted in a randomized block design comprising of eight treatments i.e. 50% NPK, 100% NPK, 150% NPK, 100% NP, 100% N, 100% NPK+ farmyard manure (FYM) @ 15 t ha−1 yr−1, 100% NPK-S and unfertilized-control, with four replications. Soil samples from all treatments were collected from 0–15 cm depth and biochemical properties were determined. Significant increase in soil organic carbon was recorded with 100% NPK + FYM @15 t ha−1. The availability of N, P, K, S, soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN) were increased significantly with the integrated application of fertilizers and FYM over control and other fertilizer treatments. Further, the conjoint use of fertilizers and FYM was also significantly superior to other treatments in terms of activities of soil enzymes like dehydrogenase, acid phosphatase, alkaline phosphatase and βglucosidase. The correlation studies revealed significant positive relationship of available N, P, K and S, SMBC, SMBN, dehydrogenase activity, alkaline phosphatase activity, acid phosphatase activity and βglucosidase activity with total productivity of soybean and wheat crops.

Soil and plant samples were collected after harvest of wheat in 2010 from a long-term experiment on groundnut-wheat sequence that continued since 1996–97 on a Vertic Ustochrept at Junagadh Agricultural University, in order to study the distribution of boron (B) in different fractions and their contribution towards B availability in soil and B uptake by wheat. Treatments included N alone, NP, NPK, 150% of recommended NPK, NPK+farmyard manure (FYM) and an unfertilized control. Five soil B fractions were determined along with hot CaCl2-extractable (available) B. Specifically adsorbed and organically bound B fractions were significantly greater under continuous use of NPK+FYM compared with other treatments, resulting in higher values of available B under NPK+FYM treatment. Soil organic C and cation exchange capacity were the important soil characteristics that governed the distribution of soil B in different fractions. Organically bound B appeared pivotal regarding availability of native B for plant uptake.

Improving soil organic carbon (SOC) and nitrogen (N) in arable soils is one of the important strategies to enhance soil quality for sustainable crop production and to mitigate climate change. Hence, we investigated the changes in SOC and N under conservation agriculture (CA) in an alluvial soil of the north-western Indo-Gangetic Plains (IGP) after two years of rice (Oryza sativa L.)-wheat (Triticum aestivum L.) rotation. The treatments were: Puddled transplanted rice followed by conventional-till wheat (TPR-CTW), TPR followed by zero-till wheat (TPR-ZTW), Direct-seeded rice followed by ZTW (DSR-ZTW), DSR-ZTW with rice residue retention in ZTW (DSR-ZTW+RR), DSR-ZTW with Sesbania brown manuring (DSR+BM-ZTW), DSR+BM-ZTW+RR, DSR-ZTW with ZT summer mungbean (greengram) (Vigna radiata) as a relay crop and mungbean residues retained on rice fields as in-situ green manuring (MBR+DSR-ZTW-ZTMB) and MBR+DSR-ZTW+RR-ZTMB. Results indicated that plots under CA (MBR+DSR-ZTW+RR-ZTMB) had significantly higher Walkley-Black C, KMnO4-C and very labile SOC compared with TPR-CTW in surface (0–15 cm) soil. Interestingly, addition of residues with mixed C:N ratios (legume and rice residues) failed to register improvement in soil mineral N, owing possibly to greater portioning of N towards soil microbial biomass (SMB) and particulate organic matter (POM) associated pools. Fascinating results could be expected in the present experiment with the passage of time.