B. S. Brar

Soil Nitrogen Fractions in Relation to Rice-Wheat Productivity: Effects of Long-Term Application of Mineral Fertilizers and Organic Manures

ABSTRACT Major portion of soil N, present as organic fractions (SON), plays an indirect but vital role in N nutrition of plants. The SON fractions are sensitive to management practices, including fertilization. The nature and distribution of different forms of soil N were studied under long-term use of mineral fertilizers and organic manures in a rice (Oryza sativa)-wheat (Triticum aestivum) cropping system. Long-term fertilizer treatments included control (T1), 100% N (T2), 100% NP (T3), 100% NPK (T4), 150% NPK (T5), 100% NPK plus straw (T6), 100% NPK plus green manure (T7), and 100% NPK plus farmyard manure (T8). Prolonged application of fertilizers and organic manures differentially influenced mineral N (NO3–-N and NH4+-N), organic N fractions, and total N in soils. Organic N fractions constituted about 94.2% of total N as compared with 5.8% share of mineral N. Nitrate N was the dominant mineral N fraction in the soil, which was 4.4 times higher than NH4+-N fractions. Application of fertilizers improved available N in soil. Hydrolyzable-N increased with the application of organic manures. Of the total hydrolyzable-N fractions in soils, ammonia-N was 25%, amino sugar-N 9.9%, amino acid-N 25.2%, and hydrolyzable unknown-N 39.8%. A significant positive correlation was recorded between crop yield and N uptake. Amino acid-N and amino sugar-N explained 82.9% of the variation in rice yield and 73.4% of the variation in wheat yield. Integrated use of organic manures and inorganic fertilizers improved the N fractions in the soil, which should help increase rice and wheat production.

Cropping System Impacts on Carbon Fractions and Accretion in Typic Ustochrept Soil of Punjab, India

Implementation of best management practices (BMPs) to increase crop productivity by intensive cultivation on marginal/fallow lands has positive impact on soil organic carbon (SOC). Because of difference in BMPs, impact of cropping system (CS) on SOC is not similar across soil types. Therefore, this study evaluated the relative influence of 10 different CSs on important SOC fractions and accretion in Typic Ustochrept of Punjab, India. Conversion of fallow lands to agricultural systems for eight years significantly increased SOC concentration in 0–15 cm layer. However, keeping the field fallow for the same period decreased SOC concentration by 24% from antecedent level of 3.8 to 2.8 g C kg−1. Among different CSs, significant differences in SOC concentration was recorded in crops amended with farmyard manure (FYM). All maize (Zea mays L.)-based CSs contained significantly higher SOC concentration as compared with that in rice (Oryza sativa), cotton (Gossypium hirsutum), and groundnut (Arachis hypogaea)-based CSs except for the groundnut-potato (Solanum tuberosum)-bajra (Pennisetum glaucum), which also received FYM. While comparing three important CSs of the region, maize-wheat cropping system had 5.6% higher labile carbon (LC) than for cotton-wheat, and was 7.3% higher in rice-wheat system. On an average, among different CSs, maize-based CSs had the maximum SOC pool, followed by that in groundnut, cotton, and the minimum in rice (31.3 Mg C ha−1)-based CS in 0–60 cm soil profile. The rice equivalent yield ranged between 6.9 Mg ha−1 to 38.6 Mg ha−1 under different CSs.

Temporal Variations in N2O Emissions in Maize and Wheat Crop Seasons: Impact of N-Fertilization, Crop Growth, and Weather Variables

ABSTRACT Nitrous oxide (N2O) emission from agricultural soils is one of the important contributors to global greenhouse gas (GHG) emissions. The impact of crop growth and weather variables on N2O emissions during maize (Zea mays L.) and wheat (Triticumaestivum L.) crop seasons in unfertilized soils (TC) and N (nitrogen) fertilized soils (TN) was studied in a field experiment in Punjab, India. The fluxes were measured via closed chambers and a gas chromatography. In the maize crop season, N2O fluxes in TC ranged from 11.1 to 61.2 N2O-N g ha−1day−1, and in TN ranged from 10.3 to 129.2 N2O-N g ha−1day−1, respectively, whereas in the wheat crop season fluxes were comparatively lower, and they ranged from 3.3 to 21.2 N2O-N g ha−1day−1 in TC and from 4.8 to 44.4 N2O-N g ha−1day−1 in TN. More than 60% of total season emissions occurred during vegetative growth stages of both the crops. N2O fluxes in both crop seasons were mainly controlled by rainfall, but the impact was marked in the maize season. Additionally, the impact of fertilizer-N application on N2O fluxes was also evident as in TN the influence of weather variables on fluxes was less by 40% than in TC. The study suggested that N2O emissions could be large during vegetative growth stages if rainfall or irrigation events coincide with N-fertilization.

Long-term Chemical Fertilization Impacts on Kinetics of K Release, Wheat Yield, and K Uptake in a Typic Ustrochrept Soil of Punjab, India

ABSTRACT Long-term experiments are leading indicators of sustainability and serve as an early warning system to detect problems that threaten future productivity. An increasing trend in yield is necessary for a system to be called sustainable. Impact of long-term use of inorganic fertilizers on kinetics of K release, wheat (Triticumaestivum L) yield, and K uptake in a sandy loam, typicustrochrept soil was studied under maize (Zea mays L)-wheat cropping sequence. Potassium release was higher in K-treated soil than in K-minus soil. Potassium released from clay fractions after 264 h was 3.1 and 6.2 m mole kg−1 for without-K (soil I) and with-K fertilization (soil II), respectively. The amount of K released from silt fractions was 2.1 and 3.4 m mole kg−1 for soil I and soil II, respectively. Lowest amount of K release was recorded in a sand fraction which was 1.1 and 2.1 m mole kg−1 for soil I and soil II, respectively. Elovich equation fit well and explained the nonexchangeable K release in these soils. Higher rate constant values were observed in soil receiving K fertilizer as compared with without-K application. Grain yield of wheat increased significantly with the increase in K from 0 to 41 and 82 kg K ha−1. The K uptake was higher than the K applied to wheat indicating that nonexchangeable K contributed toward its uptake in wheat crop. The application of K helps to reduce the mining of K from nonexchangeable form, which results in yield increase in wheat.