Soil organic matter and biological properties after 26 years of maize–wheat–cowpea cropping as affected by manure and fertilization in a Cambisol in semiarid region of India

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Abstract

Balance application of inorganic fertilizers and organic amendments greatly influence the accumulation of organic matter in soil and also the soil microbial activities. An investigation was carried out to study the changes in soil organic matter and biological properties as affected by long-term application of manure and fertilizers in maize (Zea mays)–wheat (Triticum aestivum)–cowpea (Vigna unguiculata) cropping system in a Cambisol in semi-arid region of India. The crop yield, soil organic C and total N and mineralizable C and N increased with the application of inorganic fertilizers. However, there was greater increase of these parameters when manure was applied along with inorganic fertilizers. Soil microbial biomass C was increased from 122 mg kg−1 in unfertilized treatments to 331 mg kg−1 in soil amended with 100% NPK+manure. The dehydrogenase, urease and alkaline phosphatase activities closely followed the soil organic carbon content and increased significantly with the addition of balanced nutrients and manure. The results indicated that soil organic matter content and soil microbial activities, vital for the nutrient turnover and long-term productivity of the soil, are enhanced by balanced application of nutrients and manure.

Introduction

Present day concern regarding the long-term productivity and sustainability of agro-ecosystems is leading to the development of new approaches which are able to maintain and protect soil resources (Harris and Bezdicek, 1994). The issue is directly related to maintain the quantity of soil organic matter which is a critical component of soil productivity. The level of organic matter in soil is considered to be a function of the net input of organic residues by the cropping system (Gregorich et al., 1996). Therefore, soil and crop management practices such as cultivation, crop rotation, residue management and fertilization exert a considerable influence on the level of organic matter retained over time. The benefits of balanced fertilization using crop residues, organic manure and green manuring in maintaining soil organic matter levels have been increasingly emphasized (Ladd et al., 1994, Chander et al., 1997).

Soil biota are considered an important and labile fraction of soil organic matter involved in energy and nutrient cycling. It has been well established that the more dynamic characteristics such as microbial biomass, soil enzyme activity and soil respiration respond more quickly to changes in crop management practices or environmental conditions than do characteristics such as total soil organic matter (Dick, 1992, Doran et al., 1996). Much information is available on the build-up and turnover of soil organic matter and its various fractions under temperate conditions.

Under tropical conditions where the turnover rate of soil organic matter is comparatively rapid (Chander et al., 1997), only few studies have been conducted on soil organic matter dynamics and soil microbial activities in relation to application of inorganic fertilizers or organic amendments (Goyal et al., 1993, Goyal et al., 1999). The present study was undertaken to ascertain the changes in soil organic matter level, microbial biomass and soil enzyme activities as influenced by the long-term application of fertilizers and manure to maize–wheat–cowpea cropping system in semi-arid region of India.

Section snippets

Description of field experiment

Ten treatments were selected from a long-term experiment at Indian Agricultural Research Institute, New Delhi, India (28°37′–28°39′N latitude and 77°9′–77°11′E longitude). The experiment was started in 1971 on Cambisol (540 g kg−1 sand, 170 g kg−1 silt and 290 g kg−1 clay) with a maize–wheat–fodder cowpea cropping sequence. The initial soil pH was 8.3, electrical conductivity 0.45 dS m−1, CEC 10.6 cmol (p+) kg−1, organic carbon 4.4 g kg−1, NaHCO3-extractable P 16 kg ha−1, NH4OAc-extractable K 155 kg ha−1 and

Soil C and N

Grain and drymatter yield of all the three crops (data not shown) increased significantly with fertilizer nutrients and manure application thus emphasizing the essentiality of balanced nutrition attaining maximum crop yields. The response of crops (mean of 26 years) was directly related to the build-up of soil organic matter in the soil due to nutrient and manure application over the years (Fig. 1). The organic C and N contents presented in Table 1, provide a measure of organic matter status of

Conclusions

The data obtained from semi-arid sub-tropical conditions suggests that, as compared to unbalanced and sub-optimum fertilizer application, the organic C status in soil was improved by balanced application of chemical fertilizer nutrients and manure. The yields of all the three crops namely wheat, maize and cowpea showed a strong relationship between the organic carbon build-up in soil reflecting in greater C inputs, C and N mineralization and better crop productivity in these treatments. Soil

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