The present study aims to determine fertilizer (N–P–K) recommendations for maize (Zea mays L.) on Acrisols (south Benin) and Ferric and Plintic Luvisols (centre Benin). Two years (2011 and 2012) experiment was conducted at Dogbo and Allada districts (southern) and Dassa (centre Benin). Six on-farm experiments were carried out to validate fertilizer rates simulated by the DSSAT model. The experimental design in each field was a completely randomized bloc with four replications and ten N–P–K rates: 0–0–0 (control), 44–15–17.5 (standard fertilizer recommendation for maize), 80–30–40, 80–15–40, 80–30–25, 80–30–0, 69–30–40, 92–30–40, 69–15–25 and 46–15–25 kg ha⁻¹. Treatments 44–15–17.5 and 46–15–25 showed the lowest grain and stover yields. The observed maize grain yields were highly correlated with the estimated grain yields (R² values varied between 80 and 91% for growing season 2011 and between 68 and 94% for growing season of 2012). The NRSME values varied between 12.54 and 22.56% (for growing season of 2011) and between 13.09 and 24.13% (for growing season of 2012). The economic analysis for the past 32 years (1980–2012) including the current experiment showed that N–P–K rates 80–30–25 (at Dogbo), 80–15–40 (at Allada) and 80–30–0 (at Dassa) were the best fertilizer recommendations as they presented the highest grain yields and the best return to investment per hectare. Nevertheless, 80–30–25 is advised for Dassa considering that sustainable maize production will require regular inputs of potassium. The 2 years of field experiments were not sufficient to derive biophysically optimal fertilizer recommendation rates for each site.

Four on-farm experiments in central Benin examined whether land-use succession and fertilizer treatments for prior cotton would sustain subsequent maize crop yields and achieve balanced plant nutrition. Treatments consisted of three prior land use successions, i.e. before planting maize (egusi melon-cotton-cottonmaize, cotton-maize-cotton-maize and cassava-maize-cotton-maize) including for each, four replications of three fertilizer treatments: recommended practice [150 kg ha^-1 of 14-23-14 (NPK) plus 5S-1B, applied 25 days after sowing and 50 kg ha^-1 of urea on 40 days after sowing], NPK-SB mixed with urea (the recommended amount of NPK-SB and urea are mixed then applied 40 days after sowing) and reduced NPK-SB dose (recommended practice, but the amount of NPK-SB is reduced to 100 kg ha^-1). Prior cotton and subsequent maize yields and nutrient uptake were not significantly affected by fertilizer treatments. Furthermore, fertilizer treatments had no significant effect on soil chemical properties before planting the subsequent maize crop. Land use types had significant effect on cotton yields, soil chemical properties, subsequent maize yields and nutrient uptake. The lowest yield and nutrient uptake were registered in the cotton-maize-cotton-maize land use succession and the highest in the egusi melon-cotton-cotton-maize succession. For sustainable soil fertility management, adoption of adequate crop succession system and recommended fertilizer application practice are suggested. Keywords: Crop rotation, technology adaptation, soil fertility, residual effect, maize cultivation, balanced nutrition

The present study aims to assess the biodiversity of arbuscular mycorrhizal fungi (AMF) associated with cashew (Anacardium occidentale L.) cultivars characteristics in Benin (West Africa). 108 soil samples were collected at 0-20, 20-40 and 40-60 cm depth under cashew trees at Glazoué in the centre Benin. Cashew’s cultivars characteristics regarding nut and apple size, apple colors and classes of Diameter at Breast Height (DBH) were the treatments. Soil chemical properties, AMF spores’ density and the diversity of AMF in the soil were assessed. Plantation of cashew improved the stock of soil organic carbon (11.24±0.63 and 10.93±0.71 g/kg for 0-20 cm soil depth respectively for cultivars producing big nuts and big apples and cultivars producing small nuts and small apples) and total nitrogen content (1.29±0.11 and 1.21±0.12 g/kg for 0-20 cm soil depth respectively for cultivars producing big nuts and big apples and cultivars producing small nuts and small apples) but it depletes available phosphorus (36.86±6.53 and 41.42±9.22 mg/kg for 0-20 cm soil depth respectively for cultivars producing big nuts and big apples and cultivars producing small nuts and small apples) and exchangeable potassium (0.93±0.10 and 0.79±0.04 cmol/kg for 0-20 cm soil depth respectively for cultivars producing big nuts and big apples and cultivars producing small nuts and small apples). Seven species of AMF (Scutelospora gregarine, Acaulospora colossica, Acaulospora lacunosa, Enthrophospora infrequens, Glomus hoi, Glomus geosporum and Glomus sp.) were identified. They belong to three families and four genera. The species belonging to Glomeracea family were dominants (91.8%) against 5.5% and 2.7% respectively for the Gigasporaceae and Acaulosporaceae. In general, the average numbers of AMF spores were 5.63±0.26; 3.54±0.19 and 1.94±0.15 per gramme of dry soil respectively for 0-20, 20-40 and 40-60 cm depth. The community of AMF was fairly diversified in the soil under cashew’s trees. There was an equitable distribution of AMF genera associated with cashew’s cultivars characteristics tree.

Recent studies reported the important contribution of animal dejections as organic manure for crop production but, little is known on the decomposition rate and nutrient release pattern in wetland of the manure of pigs nourished with diet enriched with Azolla filiculoides. A litter bag study was carried out under full control during 6 weeks in pots containing 25 liters of tap water and 15g of pigs’ dejection in each decomposition bag. The experimental design was a completely randomized block design with three replications. The treatments consisted of dejections of pigs nourished with : T1 (recommended diet composition) consisted of 15% Azolla + 55% provender + 5% coconut copra + 5% oil palm + 5% soybean bran + 10% rice bran + 5% kitchen waste ; T2 (partially improved diet with Azolla) consisted of 30% Azolla + 65% rice bran + 5% oil palm ; T3 (improved diet with Azolla) consisted of 47.5% Azolla + 47.5% rice bran + 5% oil palm; and T4 (improved diet with cereal bran) consisted of 15% Azolla + 40% rice bran + 40% wheat bran + 5% oil palm). Four pigs per diet were considered leading to 16 white landrace pigs of six months age. Decomposition rates in water were significantly (P < 0.05) fast during the first week and became very slow during the following weeks. After the six weeks of experiment, 58.2 % of manure from treatments T1 and T4 were decomposed against 47.2 % for T2 and T3. However, 40.1, 53.3, 67.4 and 57.1% of total N content in treatments T1, T2, T3 and T4 respectively were released. As consequence, manure from improved diet with Azolla (T3 and T2) are suggested for integrated rice and fish production system. Nevertheless, decomposition and nutrients (P, K, Ca and Mg) release patterns had significantly (P < 0.05) increased in water in treatments T1 and T4 compared with the two treatments containing more Azolla in the diet (T2 and T3).