Effects of straw mulch on growth and yield of durum wheat during transition to Conservation Agriculture in Mediterranean environment.

tIn Mediterranean environment, the transition to Conservation Agriculture (CA) poses as major issue thescarce accumulation of residues on soil surface; covering the soil with additional straw mulch could bea proven strategy for soil and water conservation, especially where durum wheat is the main crop, untilreaching a layer of adequate thickness, typical of the stabilized CA systems.Two field trials were carried out from 2010 to 2012 in a representative area of Southern Italy during thefirst two years of transition to CA. Durum wheat was grown under three increasing levels of straw addedas soil mulching: 5.0 t ha−1(100% mulch cover (100%MC)), 2.5 t ha−1(50%MC) and 1.5 t ha−1(30%MC), plusa CONTROL. The influence of such additional straw on soil water and nutrient availability, physiologicaltraits, growth and yield of durum wheat was assessed, as well as the necessary amount of additionalstraw was estimated.Both years of study indicated that root-zone moisture contents, monitored at 5 cm depth starting fromthe beginning of head emergence, were significantly improved by mulching, with the highest differencesdetected between 100%MC and CONTROL (36 and 41% higher in 2011 and 2012, respectively). 100%MCexhibited also the significant lowest concentration of nitrate-N (9 mg L−1on average), K, Ca and Mgin soil solution. Additional straw at higher rates improved crop physiology: leaf water content (LWC)was highest in 100%MC (48.3%) and lowest in CONTROL (38.2%); SPAD and NDVI values (chlorophyllcontent) were respectively increased by 25% and 22% in 100%MC and by 15% and 17% in 50%MC, withrespect to CONTROL. Nitrogen Nutrition Index (NNI) at anthesis was highest in 100%MC (0.97 vs. 0.50in CONTROL). Significant high correlations were found between yield components and water as well asNO3−availability in soil solution (number of grains m−2vs. NO3−in soil solution R20.89; number ofgrains m−2vs. soil water R20.96). Yield was significantly affected by crop dry weight and N status atanthesis (0.49 kg m−2in 100%MC vs. 0.27 kg m−2in CONTROL, averaged over years). Moreover, the plotswith higher amount of additional straw (100%MC and 50%MC) promoted significantly the accumulationof nitrogen in grains (0.56 mg N grain−1in 2011 and 0.51 mg N grain−1in 2012 in 50%MC).Under our experimental conditions, 1.5 t ha−1of straw added as mulching are enough to significantlyproduce higher yields, although to exert significant positive effects both on soil and on crop physiologicalindicators, 2.5 t ha−1of wheat straw are necessary. However, increasing the amount of crop residues until5 t ha−1, crop performances and soil characteristics continue to significantly improve.