Effect of N fertilizer source and timing on yield and N use efficiency of rainfed maize (Zea mays L.) in Kashmir–Pakistan

Abstract

Efficient N fertilization is considered one of the most important management strategies for sustaining or increasing crop yield and quality, and improving nitrogen use efficiency (NUE). A 2-yr (2008–2009) field experiment with rainfed maize (Zea mays L.) was conducted in the hilly region of Rawalakot Azad Jammu and Kashmir (AJK), Pakistan to evaluate the effect of time and source of N fertilizer application on the growth, yield, N-uptake and NUE of maize. The experiment consisted of a factorial arrangement of 2 years, two methods/timings and four N sources including a control, arranged in a completely randomized block design replicated three times. Treatments included two application timings i.e. single application of N at planting and a split application i.e. 1/2 at sowing + 1/2 at V₆ stage, and three N fertilizer sources i.e. urea, calcium ammonium nitrate (CAN), and ammonium sulfate (AS), and a control. Results indicated that response of growth characteristics to N sources was in the order CAN > AS > urea. Similarly, straw and grain yields were highest in CAN followed by AS while urea exhibited the lowest. The relative increase in grain yield by CAN and AS was 11 and 10% in 2008 and 8 and 5% in 2009 over urea N. Split application of N increased grain yield between 4 to 9% in 2008 and 3% in 2009 over single N application. The amount of N taken up by plants depended upon the source of N fertilizer and was in the order urea > CAN > AS. The NUE ranged between 31 to 61% in 2008 and 40 to 67% in 2009 and urea exhibited the highest NUE. Split application of N increased NUE by 23 and 21% over single N application. Results of this study indicated that yield and N balance of maize was significantly affected by N sources and application timing. However, response of both traits to N sources was distinctive. Further studies (long term basis) are suggested to explore the effects of N sources on maize productivity particularly yield and N balance relationship.

Introduction

Application of N through chemical fertilizers is the dominant and main source of N input in the crop production systems world-wide. Currently, 50% of the human population relies on N fertilizer for food production while about 60% of global N fertilizer is used for producing the world's three major cereals: rice, wheat, and maize (Ladha et al., 2005). Unfortunately, fertilizer N is not utilized efficiently in the world agriculture and the recovery of N in soil−plant system seldom exceeds 50% of applied N. In cereals N recovery efficiency at global level is reported to be less than 40% (Raun and Johnson, 1999, Raun et al., 2002). The low recovery efficiency of N is associated with its losses by leaching, denitrification, volatilization and soil erosion (Fageria and Baligar, 2005). Furthermore, the dynamic nature of N, its mobility and transformation processes in soil make it an element not utilized efficiently. Raun and Johnson (1999) have calculated that the unaccounted for 67% of applied N fertilizer represents a $15.9 billion annual loss (assuming fertilizer–soil equilibrium) and even a 1% increase in N recovery would result in global savings of $234 million (Glass, 2003).

Therefore, nitrogen use efficiency (NUE) of applied mineral N fertilizer is a real concern to the researchers engaged in N cycling and N transformations. To improve N efficiency in agriculture, N management strategies that take into consideration improved fertilizer along with soil and crop management practices are necessary. Among these management strategies, adequate rate, appropriate source and timings of fertilizer application during crop growth cycle play an important role (Abbasi et al., 2012, Fageria et al., 2006). Such practices not only increase yield but also reduce cost of production and environmental pollution.

Application timing is one of the management strategies that can influence the efficiency in which applied N is utilized by crops (Randall and Vetsch, 2005, Randall et al., 2003, Ruiz-Diaz and Sawyer, 2008). Split applications of N fertilizer are often recommended as a way to reduce N losses and to improve NUE. In maize, split application of N at six leaves stage (V₆) stage increased grain yield (10.5 vs. 11.2 Mg ha^− 1) and N uptake (168 vs. 192 kg ha^− 1) compared with single N application at planting (Sainz Rozas et al., 2004). In another experiment, N recovery was increased (from 58% to 71%) and N losses were decreased (2.6–5.5% vs. 0.4–1%) in split application compared with single N application at planting (Sainz Rozas et al., 1997). However, there are also reports that split application of N fertilizer to different crops did not affect their performance and productivity (Garrido-Lestache et al., 2005, Zebarth et al., 2004). Liu and Wiatrak (2011) reported that splitting N into two doses i.e. all N at planting and at V₆ growth stage had no effect on maize grain yield and plant characteristics.

The form or the source of added N plays an important role in regulating N transformations, changing N loss patterns and influencing NUE (Ladha et al., 2005). Urea, ammonium sulfate (AS) and ammonium nitrate (AN) or calcium ammonium nitrate (CAN) are the main N carriers used worldwide in crop production (Fageria and Baligar, 2005). However, urea is generally favored by the growers over AS and AN or CAN due to lower application cost because urea has a higher N analysis than AS and AN/CAN (46% vs. 21, 33 and 26% N, respectively). Few studies had been reported previously on the comparative effects of different N fertilizer sources on the growth and yields of crops and response was generally inconsistent. Fageria et al. (2011) conducted two greenhouse experiments on rice with urea and AS and reported that the maximum grain yield and N-uptake at average N rate (160 mg kg^− 1) was 22 and 15% higher with AS compared to urea. The comparative effects of urea and AN on meadow bromegrass (Bromus bibersteinii) at two sites in central Alberta, Canada indicated that AN generally produced higher DMY (16–26%), protein yield (21 and 37%), NUE (16 and 26%) and % N recovery (20 and 38%) compared with urea (Malhi, 1997). In our previous study conducted on grassland soil, NH₄⁺ source of N was found superior to NO₃⁻ source. In the plots where NO₃⁻–N was added as the N source, DMY was 1760–1870 kg ha^− 1, N recovery efficiency was 24%–43%, while in NH₄⁺ – N added plots, both DMY and N recovery efficiency were increased to 3190–3700 kg ha^− 1, and 39%–48%, respectively (Abbasi et al., 2005).

The effect of N fertilizer forms or sources on the growth, yield and NUE of maize under field conditions had not been reported extensively. The importance of such studies under rainfed conditions becomes critical because N availability to plants differs with N form as a result of differences in mobility of each form in soil solution. Keeping this in view, the objective of the present study was to determine the effects of different fertilizer N forms/sources applied at different timings on growth and yield characteristics, N uptake, and NUE, of maize in a field experiment under rainfed mountainous conditions.