Nitrogen supply of a Dark Brown Chernozem soil and its utilization by wheat

Abstract

S. S. 2006. Nitrogen supply of a Dark Brown Chernozem soil and its utilization by wheat. Can. J. Soil Sci. 86: 483-491. Environment and management effects on the N supply to crops are not well understood. We assessed the influence of tillage system (conventional tillage or no-till), N fertilizer (0 or 60 kg N ha -1 ) and year on N sources and supply of a Dark Brown Chernozem loam soil, and N utilization by spring wheat (Triticum aestivum L.) in 2 yr. The main N source was mineralized N; only 14-23% of wheat N was derived from fertilizer, and non-exchangeable ammonium made no measurable contribution. Soil NO 3 and exchangeable NH 4 content at sowing and net N mineralization during the growing season (N min ) were influenced more by year than by N addition and tillage. N min was 90-100 kg N ha -1 in 1999, a moist growing season but only 21-39 kg N ha -1 in 2000, a drier year. In both years, soil inorganic N to 60 cm at sowing averaged about 60 kg N ha -1 of which half was N mineralized since the previous harvest. Year accounted for 65-81% of the variation in N uptake. Fertilization increased N uptake and wheat yields, especially in 2000, but fertilization and tillage had no effect on post-heading N uptake and N translocation. Nitrogen use efficiency (NUE) and N recovery were lower with N applied and not affected by tillage. Our study indicated that available N was affected more by environment than management. In dry conditions, when N min is low, N application may be more effective in increasing yield and N uptake than in wet years, an observation that may merit further attention. Management decisions such as cropping and tillage systems and level of fertilization, as well as climatic conditions, influence crop production and N utilization (Halvorson et al. 1999;Lopez-Bellido et al. 2000). Although increasing N application enhances N uptake by wheat, N utilization often becomes less efficient (Delogu et al. 1998;Lopez-Bellido and Lopez-Bellido 2001). Halvorson et al. (1999) found that reducing the intensity of tillage or increasing N rate from 34 to 67 kg N ha -1 generally resulted in higher yields of wheat; however, the response varied among years due to water availability. Campbell et al. (1993) reported that N utilization by spring wheat was influenced more by available water and N application rate than the placement and timing of N application, and was increased by soil NO 3 remaining in the fall and decreased by fertilizer N. Soil water limitation and high inter-annual variability in precipitation are common on the prairies (Bochert 1950), and may have a greater influence than farm management practices on nutrient utilization.

Effect of growing season rainfall and tillage on the uptake and recovery of 15N-labelled urea fertilizer by spring wheat in a semi-arid environment

“…Other studies also concluded that climatic conditions, such as seasonal rainfall, affected crop N uptake (Baethgen and Alley 1989;Soon et al 2008). In our study, it is the distribution of rainfall during the growing season that determines the efficient utilization of applied and soil N. Our previous work showed that in the semiarid Canadian prairies, rainfall in May and June correlated considerably better with wheat total N accumulation at heading than did rainfall from May to July (Soon et al 2006(Soon et al , 2008. The current study showed that 15 N (and total N) accumulation in wheat increased with May rainfall only, whereas head 15 N recovery decreased with June rainfall.…”

“…At this site, net mineralized N can be substantially higher than the amount of NO 3 -N in the surface soil layer at seeding (Soon et al 2006), and so exert a greater influence on plant N uptake than initial NO 3 ( content. Fertilizer and total N uptake in the head, straw and the above-ground growth were correlated with May rainfall.…”

“…We have previously observed, based on results from the large field plots, that there was a yield response to N fertilizer in 3 of 5 yr (Soon et al 2006(Soon et al , 2008. Two of the three years in which there was no growth response to N fertilizer had dry growing season conditions.…”

“…Soon et al (2006Soon et al ( , 2008 found that N uptake by crops in the Dark Brown Chernozemic soil zone was influenced more by growing season rainfall, particularly those of May and June, than by soil N supply or tillage systems. The uptake and recovery of fertilizer N by crops, studied by means of 15 N labelling, is affected by climatic conditions during the growth period and by management practices.…”

“…While the effects of growing season rainfall on soil N dynamics, and crop total N uptake and utilization in the semi-arid prairie region have been reported (Soon et al 2006(Soon et al , 2008, the influence of the distribution of rainfall on fertilizer N recovery has not been as well studied. A field study with 15 N fertilizer was conducted over seven years to augment information on tillage effects on fertilizer N recovery by crops.…”