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A five-season experiment was initiated to study the effects of the recycling of some organic residues on a soil-crop system of a guar-wheat rotation in a sandy clay loam soil located in the semi-arid tropics of Sudan. Treatments included: incorporation of crop residues alone after harvest (Cr þ ), with (FCr þ ) or without (FCr 7 ) inorganic fertilizer, sewage sludge (SS) and humentos (H). Grain yield of wheat in FCr þ and Cr þ treatments was significantly higher than that obtained in FCr 7 and control plots by *22762% and 1167119%, respectively. When crop residues were incorporated with inorganic fertilizer, the priming effect of crop residues on straw yield (106%) was almost double that of the priming effect of inorganic fertilizer (56%). The sustainable yield index of wheat straw dry matter for the control, crop residue, humentos, inorganic fertilizer, combined fertilizer and crop residue and sewage sludge was 28, 27, 8, 35, 21 and 38%, respectively. In general, N, P and K of straw dry matter (SDM) was in the order of FCr þ 4 FCr 7 4 SS 4 Cr þ 4 H 4 C. The findings suggest that repeated incorporation of crop residues with inorganic fertilizer and applications of SS could both sustain wheat performance in the dryland ecosystems.

Background Recycling of crop residues is essential to sustain soil fertility and crop production. Therefore, it is of crucial importance to study the decomposition of crop residues particularly in the arid tropics. The decomposition and nutrient release pattern from crop residues incorporated in the soil have rarely been investigated under semiarid climatic conditions in Sudan. Decomposition and nutrient release pattern from wheat residue were investigated in a 12 week litter bag experiment under field condition. Litter bags contain 50 g wheat residue were buried in plots cultivated with guar and treated with following treatments: crop residue (CR), recommended fertilizer ? crop residue (RF ? CR), sewage sludge (SS) and non treated control (C). In each plot of each block, 12 litter bags were buried. Four bags from each treatment were retrieved at 2, 4, 6, 8, 10 and 12 weeks of decomposition. The decomposed residue was analysed for remaining dry matter (DM), nitrogen (N), phosphorus (P), potassium (K) calcium (Ca), and magnesium (Mg) contents. Mass loss and nutrients released from wheat residue followed the exponential model, W t = W 0 9 e -kt from which the specific decay rate constants (k) and t 0.5 and t 0.95 were calculated. Results The result show that the mineral fertilization combined with crop residues (RF ? CR) resulted in the maximum decomposition and nutrient release compared to the other treatments. The half-life (t 0.5 ) values of the treatments were in the following order: RF ? CR (6.70 weeks) \ SS (8.0 weeks) \ CR (9.60 weeks) \ C (11.91 weeks). The percentage remaining DM in the litter bags followed the order C (73.25 %) [ CR (66.45 %) [ SS (59.85 %) [ RF ? CR (53.85 %). A 50 % loss of residue N was found after 8.88 weeks in the C treatment and 5.04 weeks in RF ? CR treatment. Generally, nutrient loss from all treatments in the order ofConclusions Application of mineral fertilizer or sewage sludge enhances the decomposition of low-quality residue (wheat). Therefore, it is essential to apply fertilizer in degraded soil before incorporation of crop residue with high carbon to nitrogen ratio.

Article Info Received : 08.08.2016 Accepted : 07.11.2016 A field experiment was conducted in the Experimental Research Farm of Omdurman Islamic University, Sudan to determine short-term effect of irrigation intervals (7 and 10 days) and sun-dried or composted sewage sludge, recommended mineral fertilizer on straw dry matter yield (SDMY) and N, P and K content of fodder sorghum and soil properties. In the 7 and 10 days irrigation intervals, composted, sun-dried sludge and mineral fertilizer have significantly increased SDMY over the control by 51, 98, 67 and 78, 19, 33%, respectively. Apparent N use efficiency (ANUE) in composted and sun dried plots irrigated at either 7 or 10 days was 9 -36 and 16 -74%, respectively. Reducing the irrigation interval has significantly increased salinity by 13%. Increasing irrigation interval has decreased bulk density by 5%. It could be concluded that, application of composted sludge is a useful practice for improvement of soil properties and consequent yield increase.

Background Poor physical and chemical properties of sand dune soil are the main constrains in afforestation of sand dune in desertified area. The aim of this study is to improve the physical and chemical properties of dune soil in Elrawakeeb Dry Land Station using organic wastes as a fertilizer source and amendments, for sustainable sand dune stabilization program. Salvadora persica L. seedlings were transplanted in a 2 m 9 2 m plots and treated with: sawdust (SW), chicken manure (CH), chicken manure with sawdust (CH ? SW), sawdust with inorganic fertilizer (SW ? IF), sewage sludge (SS), sewage sludge with sawdust (SS ? SW), and control (C). The treatments were arranged in a randomized complete block design with four replicates. The soil chemical properties were determined from soil samples collected from the fixed sand dune (0-20 cm depth) in the second year after application. Results Application of organic amendments significantly (P = 0.001) increased soil organic carbon by 224 %, available P by 139.9 %, total nitrogen by 142.9 %, and mineral nitrogen by 83.5 % and decreased soil pH by 5.6 %. Conclusions Incorporation of organic waste in desertified sandy dune soils increased its nutrient content and hence sustained biological fixation of sand dunes.