Introduction

Rice-wheat is the major cropping system in the Punjab and it is undoubtedly mostly through this system that India has achieved its goal of food self-sufficiency. For the past decade however, productivity of this important system has reached a plateau or even begun to decline as a consequence of depletion of native nutrient reserves, the emergence of multi-nutrient deficiencies, and an associated fall in factor productivity of applied nutrients.

Crop diversification is essential for enhancing farm income as well as for reducing excessive nutrient mining and other deleterious effects on soil health. For this purpose, the Punjab Government has outlined a plan to encourage farmers to shift from a rice-wheat rotation and introduce more profitable crops to replace traditional cereals. This policy aims to diversify at least one million hectares away from the rice-wheat crop rotation to legumes, pulses, vegetables, and other high value crops.

For successful implementation of the proposed crop diversification plan in the state, there is a requirement to evaluate fertilizer recommendations for the new cropping system. Special attention needs to be addressed to potassium, as the rice-wheat cropping sequence at moderate yield level of 8.8 t/ha, removes from the soil 235, 92 and 336 kg/ha/year of N, P₂O₅ and K₂O respectively (IFA World Fertilizer Use Manual, 1992). Evidently, even with the recommended rate of fertilization, a negative nutrient balance is being noticed particularly for K.

In this study, we have evaluated the effect of balanced application of fertilizers on the yield of crops under a sunflower-maize-pea cropping system with the aim of establishing the most appropriate rates of application of potassium for optimum yields.

Effect of potassium application on the yield and yield parameters of sunflower

Three field trials, two at farmers' fields and one at Krishi Vigyan Kendras (KVK) Bahowal in Hoshiarpur district were conducted during Rabi, 2006. KVK centers were established to train farmers in various occupations related to agriculture in all districts of the Punjab, to help the trainees generate self-employment and to help the farmers follow modern techniques of farming.

The physico-chemical properties of soils are reported in Table 1.

Five treatments viz. 60:0:0; 60:30:0; 60:30:30; 60:30:60 and 60:30:90 kg N:P₂O₅:K₂O per ha were applied. The crop was grown following randomized block design (RBD) with three replications at each location of the experiment. All the di-ammonium phosphate (DAP), muriate of potash and half of urea was applied at sowing and the second half of urea was applied after 30 days (DAS).

The application of both P and K increased the yield of grain and straw of sunflower and an optimum yield of 23.0 q/ha was obtained with combined application of N₆₀P₃₀K₉₀ (Table 2). Addition of K at the rates of 30, 60 and 90 kg K₂O/ha increased average grain yield by 8.6, 6.2 and 10.0 per cent over application. The agronomic efficiency of potassium application (AE_K) was calculated to be 6.0 kg grain per kg K₂O application. Application of potassium at the rates of 30, 60 and 90 kg K₂O/ha increased the straw yield by 6.1, 12.1 and 11.9 per cent over NP application with an agronomic efficiency of 8.7 kg straw per kg of K₂O applied.

Growth and yield parameters were enhanced by K application (data not shown). Potassium increased the 1000-grain weight, head diameter, plant height, the stem girth of plants and total leaf area. Fresh harvested head yield increased by 25.7, 13.2 and 30.0 per cent with the application of 30, 60 and 90 kg K₂O/ha, respectively over NP application. Grain to head ratio, which reflects photosynthate partitioning efficiency of crop plants increased in response to K application. Stems of the plants from the balanced fertilized treatment (NPK) were much thicker than those of the imbalanced fertilized treated plants (NP only).

Total leaf area increased significantly with application of K as compared with NP thereby enabling a greater production of photosynthates in the balanced fertilized crop.

Potassium application increased both oil content and oil yield (Fig. 1). The oil yield of 696 kg/ha was obtained with 90 kg K/ha application as against 392 kg/ha with imbalanced fertilization (NP only).

Effect of potassium application on the yield and yield parameters of maize

Four field experiments, three at a farmers' field and one at KVK in the Hoshiarpur district were conducted during kharif 2006 to predict the response of maize to K application in soils testing low to medium in available K. Physico-chemical properties of the soils are reported in Table 3.

Five treatments viz. 125:0:0; 125:60:0; 125:60:30; 125:60:60 and 125:60:90 kg N:P₂O₅:K₂O per ha were applied. The crop was grown following RBD with three replications at each site. Nitrogen and phosphorus were applied uniformly to all the plots at 125 kg N/ha and 60 kg P₂O₅/ha as urea and di-ammonium phosphate (DAP). All the phosphorus and one third of the amount of N was applied at sowing, a third of the N when the crop was at knee-high stage and the remaining third at the tasseling stage. Potassium was applied as muriate of potash at sowing. The crop was manually harvested at maturity.

The grain yield of maize increased with increasing levels of K up to 90 kg K₂O/ha at all the sites (Table 4).

Imbalanced application of fertilizer, with addition of only N recorded the average yield (4 sites) of 46.6 q/ha. The addition of phosphorus and potassium increased the yield further. However, optimum yield of 60.3 q/ha was obtained with the combined application of N, P and K at the rates of N₁₂₅, P₆₀ and K₉₀ kg/ha. Additional doses of K at the rates of 30, 60 and 90 kg K₂O/ha along with combined application of N and P increased the average grain yield by 3.3, 11.7 and 26.1 per cent. The much lower yields at KVK Bahowal than elsewhere were the result of comparatively poor stand of the crop due to excessive soil moisture conditions caused by excessive rain. The highest yield of all the sites was at Sakrooli, which may have resulted from the comparatively high fertility status of this soil. Thus the yield of maize in general, was related to the fertility status of the different experimental sites. However, NPK application enhanced yields at all sites irrespective of differences, in fertility status, varietals differences, and crop management practices adopted.

Application of K resulted in significantly bigger cobs with more length, girth and number of grain lines at most sites, compared to those produced from the NP treatment. Increased cob length, girth and number of grain lines per cob in turn increased grain weight per 100 cobs and 100 grains weight. Growth parameters viz. plant height, plant girth and leaf area index were also positively influenced by potassium application (data not shown).

The protein content of maize was increased with balanced application of fertilizers (Fig. 2). Hence the balanced fertilization not only increased the yield but also improved the quality of maize.

Effect of potassium application on the yield and yield parameters of peas

Vegetable (green) pea is an important winter season crop of the Punjab and is mainly grown in the Hoshiarpur, Nawanshehar and Ropar districts. The soils of these districts are low to medium in available potassium. Green peas, being a short duration crop, are likely to respond to the application of potassium.

To study the effect of potassium on the yield of green pea, experiments were conducted at Krishi Vigyan Kendra (KVK), Bahowal, Nangal Khurd, and Sakrooli (District Hoshiarpur). Various physico-chemical properties of soils from various experimental sites are listed in Table 5.

Five treatments viz. N₅₀P₀K₀ N₅₀P₀K₀, N₅₀P₆₀K₀, N₅₀P₆₀K₃₀, N₅₀P₆₀K₆₀ and N₅₀P₆₀K₉₀ (N, P₂O₅ and K₂O, kg/ha) were applied at all sites. The crop was grown following RBD with three replications at each location. A recommended dose of 50 kg N/ha as urea and 60 kg P₂O₅/ha as diammonium phosphate was given at the time of sowing. This was carried out in mid October 2004 at all the experimental sites using the variety Arkel.

Yield of fresh pods of green peas, which is an important parameter since the crop is sold as green pods for vegetable purposes, was increased over the control by application of K at all the sites (Table 6). At KVK Bahowal, Sakrooli and Nangal Khurd highest pod yield increased the number of pods per plant, the 100 pod weight and grain weight from 100 pods (data not shown). The effect of potassium application was to increase all the factors such as number and weight of pods per plant contributing to a higher yield of peas. The yield of fresh grains is an important criterion, particularly in a crop like green pea as it indirectly determines its price in the market. An increase in yield to the extent of 44.7 per cent was observed with application of 90 kg K₂O/ha, over N and P treated plots. The highest AE_K of 4.7 kg fresh grain with application of 1 kg K₂O/ha was obtained (Table 6). The results of this study clearly indicated the need for a balanced fertilizer application, especially with potassium in order to obtain the optimum yield of crops. It was also established that the sunflower-maizepeas cropping system is a good alternative to a rice-wheat system, particularly in an area with a scarcity of water. Since this cropping system also includes oilseed, cereal and vegetable (pulse) in the rotation, soil health and crop productivity will be sustained as compared to cereal-cereal system. The system is particularly suitable because of the very fast rate of groundwater depletion in the Punjab.

Edited by E. A. Kirkby.