Integrated Nutrient Management for Sustaining Irrigated Cotton-Wheat Productivity in Aridisols of Pakistan

Abstract

Fie ld-scale information on nutrient status of farmers' grown crop pl ants and assoc iated soils can help in arriving at strategies for effective and effi cient management of the nutrient defic iencies. Therefore, a nutrient indexing of farmer-grown cotton (Gossypium hirsutum L.) and subsequent wheat (Triticum aestivum L.) was conducted by sampling diagnostic leaves, at recommended growth stages, and associated soils from randomly selected 70 fields within 7153 km2 area of Rahim Yar Khan district of Pakistan. The sampled fields represented 16 soil series belonging to two Soil Orders, i.e., Aridisol and Entisol. The soils were alkaline in pH, calcareous, low in organic matter and medium textured, as sandy clay loam and loam were the dominant textural classes. As indicated by soil analysis results, the extents of nutrient deficiencies in surveyed fields were: N, 56% and 66%; P, 60% and 51%; K, 8% and 10%; Zn, 53% and 54%; B, 41% and 37% in cotton and wheat fields, respectively. However, the extent of nutrient deficiencies indicated by plant analysis were slightly variable, i.e., N, 43% and 50%; P, 54% and 43%; K, 14% and 17%; Zn, 47% and 44%; B, 50% and 41 % in cotton and wheat fields , respectively. Almost all the cotton and wheat fields in the district contained adequate Fe, Cu and Mn. A fairl y good relationship existed between plant nutrient contents and surface so il nutrient contents, verify ing the effectiveness of the used soil tests in diagnos ing nutrient defic iencies and predicting the need for fertilizer use in cotton-wheat system. Good relationship between major and micro-nutrients contents extracted by ' universal ' soil test for alkaline soil s, i.e., AB-DTPA, and standard/routine soil tests verified effectiveness of the multinutrient test for determining field -scale fertility status of soils. Similarly, HCI extraction for B was equally effective for predicting B fertilizer need of the alkaline-calcareous, low organic matter cotton soils. The nutrient indexing data of selected soil parameters and nutrient contents in soils and associated cotton and wheat plants, were mapped using geostatistical technique of semivariogram analysis and computer graphics. Isarithm maps, so prepared, effectively delineated areas of nutrient deficiencies within Rahim Yar Khan district and, thus, would help focus future research and development. Also, a 5-year field experiment was conducted at two sites, i.e., Chak 5-Faiz (Awagat soil series; Fluventic Camborthid) and Chah A. Rahim (Shahpur soil series; Fluventic Camborthid) of district Multan, within cotton-wheat system in Pakistan, to investigate the VI impact of integrated nutrient management (INM) and crop residue recycling on crop productivity, nutrient uptake, yield trends, selected soil physico-chemical properties, and apparent nutrient balances. In a permanent layout, replicated fi eld treatments were: T, - Farmers ' fertilizer use practice (FP), i.e., 110 kg N ha-' in cotton and 80 kg N ha-' + 60 kg P20 S ha-' in wheat; T2 - Balanced nutrient management (BNM) using chemical fertilizers, i.e., 170 kg N ha-' + 60 kg P20 S ha-' in cotton and 140 kg N ha-' + 100 kg P20 S ha-' in wheat; T3 - Integrated nutrient management (INM) , same as T2, except that 75% N was applied as fertilizer and 25% as farmyard manure (FYM); and T4 - Same as T2, except that wheat was substituted by berseem (green manure) every alternate year and 30 kg N ha-' + 100 kg P20 S ha, was applied to berseem. In T2 to T4, 5 kg Zn ha-' as zinc sulfate and 1 kg B ha-' as borax were applied once a year prior to cotton sowing. All the above stated treatments were compared with and without crop residue (i.e., cotton sticks and wheat straw) recycling. Also, cotton was sown by two methods, i.e., on flat (conventional) bed and raised beds. Crop yields with T, treatment were generally sustained/reduced during the experimental period at both sites. Positive effect ofT2 to T4 became more pronounced during later years of the experiment, clearly showing that T, was unable to enhance crop productivity and SUppOit soil quality to sustain higher crop yield . The 5-year mean seed cotton yield with T, was 2190 kg ha-' at Chak 5-Faiz and 2452 kg ha-' at Chah A. Rahim. The T2 increased seed cotton yield by 24% over T, at Chak 5-Faiz and by 18% at Chah A. Rahim. The highest seed cotton yields were obtained consistently with T3, i.e., 4% higher than T2 at Chak 5-Faiz and 3% higher at Chah A. Rahim. However, cotton yield with T3 and T4, during year-2 and year-4 of the rotation did not differ significantly, suggesting that berseem green manuring in T4 treatment did not help increase the yield of subsequent cotton crop for this treatment. Similarly, the lowest wheat grain yields, i.e., 3025 kg ha-' at Chak 5-Faiz and 3941 kg ha-' at Chah A. Rahim, were obtained with T, . Similar to cotton, T3 consistently produced highest wheat grain yield throughout the experiment; mean grain yields were 37% higher than T, at Chak 5-Faiz and 24% higher at Chah A. Rahim. Yields with T4 (which existed during 1 st, 3rd and 5th crop season only) were close to the ones obtained with T2. On an average, T3 yielded ~ 5% greater than T2; however, nutrient-based comparison of these two treatments was not possible since FYM also supplies other nutrients. Wheat straw incorporation increased seed cotton yield by 4 % over without crop residue during 1 sl year to 7% during 5th year at Chak 5-Faiz and 2% to 5% at Chah A. Rahim. Similarly, cotton stalk residue incorporation increased wheat grain yields by 3% over without VII crop residue during 1 st year to 10% during 5th year at Chak 5-Faiz and 2% during 1 st year to 6% during 5th year at Chah A. Rahim. Mean seed cotton yield was 10% greater on raised beds than on flat bed at Chak 5- Faiz and 9% at Chah A. Rahim. Nutri ent uptake patterns by cotton as well as wheat crops resembled those of yield trends. Total nutrient uptake by both crops was relatively higher at 5-Chah A. Rahim. Also, increased nutrient uptake was recorded with crop residue incorporation; the magnitude of increase was more pronounced during later years. The INM not only improved soil NO)-N, P, K, Zn, and B fertility but also enhanced OM status, and decreased soil bulk density, with and without residue recycling. Crop residue recycling further enhanced the soil fertility parameters as well as decreased soil bulk density. Over the 5-year period, under T1, seed cotton yield trend was negative but nonsignificant, without crop residue recycling for flat bed planting at both sites. Same trend was followed by Tl with crop residue recycling for flat bed planting and without crop residue recycling for raised bed planting at Chak 5-Faiz. Contrarily, under T2 through T4, crop yield trends were positive, but non-significant at both sites. Similar to cotton, wheat grain yield trend with Tl (without crop residue recycling on flat bed) was negative, but non-significant, at both sites. Under T2 and T), wheat yield trend was significantly positive with crop residue recycling at Chak 5-Faiz, but non-s ignificantly positive at Chah A. Rahim . The experimental treatments which induced positive crop yield trends, also caused positive nutrient uptake trends except for K. INM yielded positive apparent N balance (except in Tl without crop residue recycling where N balance was negative) and positive P balance in both soils. A large negative apparent K balance was observed with all treatments at both field sites. Considering gross profits and marginal rates of return of fertilizer/manure use, the treatment T) proved to be most cost-effective at both field sites.