Maize (Zea mays L.) and Soil Response to Applying Different Management Tillage and Nitrogen Fertilizer

BACKGROUND: In the most parts of Iran, wheat residues have been traditionally burned or removed; that is often criticized for soil organic and nutrient losses, reducing soil microbial activity and increasing CO2 emission. OBJECTIVES: 1) to determine the effect on physical and chemical soil quality following 7 years of continuous application of ZT as compared to CT, crop residue management (+R and -R) and select an optimum level of N, along with suitable strategies relative to tillage and crop residues for sustainable maize yield and minimum N loss; 2) to determine the relationship between the soil quality and the crop yields. METHODS: A 7-years (2006−2012) field study was carried out at the agriculture research station of Baikola, Neka, Iran; the experiment included treatments varying in: (1) wheat straw management: plus residue (+R) and minus residue (-R); (2) tillage system: zero tillage (ZT) and conventional tillage (CT); and (3) N rates: 0 (control), 100, 200 and 300 kg N ha-1 (N1-N4). RESULT: After 7 years of continuous practice, ZT produced 40% greater maize seed yield than CT, whereas +R increased seed yield by 33% compared to -R. Seed yield of maize increased with N rate up to N3. Soil moisture content was higher under ZT than CT and with +R than -R in the 0–15 cm depth, with the highest moisture content in the ZT+R treatment in many cases. After seven crop seasons, total organic C (TOC) and N (TON), respectively, were greater by 1.275 Mg C ha-1 and 0.031 Mg N ha-1 with +R than -R, and also greater by 0.563 Mg C ha-1 and 0.044 Mg N ha-1 under ZT than CT. There was no effect of tillage, straw and N fertilization on the NH4-Nin soil in most cases, but +R treatment had higher NO3-N concentration in the 0–15 cm soil than -R. The NO3-N concentration in the soil layers increased (though small) with increasing N rate. The +R treatment had 6.7% lower proportion of fine (38.0 mm) dry aggregates, and 4.5 mm larger mean weight diameter (MWD) compared to -R treatment. Organic C, total N, moisture, aggregates stability, mechanical resistance, pH and EC were the factors that defined the difference in soil quality between conventional tillage and zero tillage. The principal component combining the variables organic C, total N, aggregate stability and moisture content showed the highest correlations with final yield (R= 0.87 for maize). CONCLUSION: The finding suggests that ZT+R would improve some soil properties, and may also be better for the sustainability of high crop production. Nitrogen fertilization, although improves crop production and some soil quality attributes, it also increases the potential for NO3-N leaching especially when applied in excess of crop requirements for optimum yield.